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Last Post 27 Apr 2017 12:49 PM by  Fair
Vorshlag Budget TT Build: Project DANGER ZONE
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16 Oct 2015 05:33 PM
Project Update for October 16, 2015: Its been another 6+ weeks since my last post, and it has been a roller coaster ride of ups and downs. The rebuilt motor finally showed up on October 6th and was a week long thrash to try to get the car together for a track test October 10th at ECR and a NASA race weekend Oct 16-18 at TWS. We had already missed the September NASA event at MSR-H so we are really pushing to get the car to the last 2015 NASA event in Texas. Unfortunately things did not go to plan and we're scrubbing this race. Let's cover what has been done since my last update to explain...

Note: After writing this update over the course of 2 weeks of work on the car, I had my thread update completed in a private section of our forum - which we use to compose and edit these mega sized build thread posts. Jason had edited everything the night before I scrubbed the event, and the morning I was going to post this (Wednesday the 14th) our forum crashed and has been down ever since. Its so borked that the server is auto-generating 20,000 error message emails a day, driving me nuts, and I have two teams of tech gurus working on fixing it (we've had that forum operational for 13+ years and its never gone down like this). Luckily I had this post open on a window on my pc, so I could copy the text, but it lost all of the UBB code for formatting, images and links. In a rush to rewrite this post now I won't link all my pics to larger images like I normally do and might miss some links I had in here before.

You will notice in this series of posts that I'm not sharing any pictures of the inside of the rebuilt motor and censoring some images where those bits are visible. I'm not going to stop sharing pictures in this build thread, as it is still part of showing "what can be done on a budget" and "what race prep we can do" at our shop, but I'm not giving any more ammunition to our competition!

Rebuilt Motor Arrives

Let's talk about TT-letter class allowable engine rebuild rules. Here they are:
Originally Posted by NASA TT Rule 8.3.i.c
18. Engine rebuild with head shave, block decking and 0.020” overbore provided that compression ratio is not increased by more than 0.5 and displacement is not increased by greater than 1.49%. Forged pistons and internals are legal; however, they must be of equal or heavier weight than the BTM parts, and points must be assessed for de-stroking, and/or increased displacement and compression ratio if greater than the limits listed above. (Note: 0.020” overbore with OEM rods and overbore pistons will yield an increase in displacement of approximately 1.1% for most engines.) If forged internals used are lighter than the BTM internals, then Dyno Re-classing (Section 8.4) should be used to prevent disqualification.

19. Engine balancing and blueprinting

20. Removal of the engine balance shaft and/or balance shaft drive mechanism

21. Non-BTM valve springs and retainers, piston rings, and rotary apex seals
My engine builder worked with me at length throughout this build, and sent plenty of images during the rebuild process, but I'm not showing any those here. NOPE.

This engine is a NASA letter class legal rebuild, with nothing out of the ordinary. I'm not going to get into the specifics of what we had done to this LT1 engine, but I will say that it was a 100% legal rebuild. No grey areas, no loopholes, just a solid TT-letter class legal engine rebuild that will likely pick up zero horsepower, only reliability. This engine would survive the most brutal tear-down protest. It is also very well built, uses all new parts, and was not cheap. The engine builder even made fun of the fact that we were having to use OEM rockers, pushrods, rocker studs, guide plates, etc. "I've never had anyone ask to use the stock stuff before!" We went over the rules with him in detail, and he is a racer himself and understands how important rules legality can be.

The engine took over 5 months to be rebuilt partly because so many of the 1992 model specific OEM parts were tough to procure (this "GenII" V8 engine family was only used from 1992-96 and the Corvettes used different parts than the Camaros or Impalas of this generation), and there were parts changes for almost every year of this LT1 - we can use any 1992-96 LT1 Corvette engine, but only as a complete assembly - no mixing and matching of parts like camshafts, heads, etc. We stuck with all 1992 stuff, but it wasn't necessarily the best choice.

There were nationwide searches to find some of the items needed, which took a lot of time. I'm not going to bore you with the trials and tribulations of building a 25 year old motor with many of the OEM parts, but it was a bit of a nightmare. And the engine builder admittedly had some inexcusable delays on his part, but it finally got here as an assembled longblock at the 11th hour, just in time to make the last NASA Texas race of 2015. Yes, this was long after 3 more NASA Texas events passed + NASA Nationals East was missed, which I was none too pleased about. We missed almost the entire NASA race schedule, but we hoped to make the last event here...

Parts Cleaned, TB Airfoil Removed, New Plug Wires + Wrapped Manifolds

The longblock was placed on the engine stand mid-day Tuesday October 6th and then the washed and cleaned Moroso oil pan was installed with a new FelPro gasket and some RTV. Then it was onto several other checks, then the intake manifold and valve covers were cleaned up on Wednesday...

These would be installed after the motor was back in the car, to save time. Some deadlines were looming: be at True Street for dyno checks and possible re-tune that Friday, then out to ECR on Saturday for track testing, then any last minute updates the following Monday-Thursday, then load up and head to TWS for a NASA weekend the next Friday-Sunday. Plus our shop was full of customer cars that all had their own deadlines, many going to the same TWS race weekend.

While the guys were putting the LT1/ZF6 drivetrain in the car Wednesday morning, I took the intake and valve covers to Friction Circle Fabrication in Lewisville to have these 25 year old parts cleaned in their UltraSonic parts cleaner. These dirty bits were soaked in the 155°F degreaser solution and agitated for 90 minutes, but they came out super clean. In hindsight we should have scraped more of the burned oil residue off the valve covers mechanically before going in the ultrasonic - would have saved a lot of time.

It is a good feeling to know your new engine isn't going to be filled with trash that fell off of some dirty part you reinstalled. And there was some serious crusty, nasty stuff on the bottom of the valve covers and inside the intake. Old, burned-on oil residue plus liquid oil in the intake - from the massive blow-by - which was being pumped back into the intake via the PCV system.

When I returned with the cleaned parts, Ryan installed the intake manifold (which was a chore - long story) plus the 25 year old OEM injectors. The stock injectors were cleaned and flow bench tested at InjectorRX in Houston back in August, and as you can see with the test results above, the flow rates were all over the map. Three of the units were also leaking and all of them were clogged before, but after they were (ultra sonic) cleaned and rebuilt they all flowed the same. Good insurance on a set of OEM injectors this old - and yes, we have to use the stock parts here, or take more class points we don't have.

The aftermarket throttle body airfoil, which we didn't know was installed until someone noticed and pointed it out from one of my build thread pictures earlier this year, was removed when the intake manifold went back on. The one NASA event where we (unknowingly) ran this airfoil on the car and actually got a class win, we had the points for it (+2 points), as we hadn't done spring upgrade yet (+2). These throttle body "air smoothing" airfoils were super common to run "back in the day" on the TPI and LT1 V8s built from 1985-1996, due to the abrupt shape change of the twin throttle body set-ups GM liked to use back then. Nowadays the LS-series GM V8 engines use a single round throttle blade, which feature smooth inlets and MASSIVE throttle blades (and flow) in comparison.

Anyway, the airfoil is no longer on the car, and is sitting on my desk as a paper weight.

With the valve covers and intake off, you get a big helping of NOPE

Before the motor went going into the car we replaced the AutoZone plug wires with some 8mm Taylor wires made for this LT1 Corvette - these are a bit easier to change with the engine out of the car. The old plug wires were still fairly decent looking, but why chance it when the motor is out? Spark plug wires are "free" per 8.3.I.c.6, for any rules lawyers that are reading, and the costs were around $65. I tend to use Taylor plug wires on everything we build around here. New NGK split electrode spark plugs were also used - we've seen good results from these and they don't have itty-bitty iridium or platinum tips that can fall off.

The OEM exhaust manifolds were also wrapped with DEI header wrap before going on, to keep a little heat out of the engine bay. As we've done throughout this build, if it has to come off or for some other reason we have to touch a part, we're going to make it better - to the limit of the rules and within sane budgetary constraints. Header wrapping the manifolds is legal per NASA TT rule 8.3.I.c.23. Ryan used an old hot rodder trick to wrap these manifolds - he pre-soaked the DEI wrap in water, to make the material more pliable during installation. It was wrapped tightly around each tube tightly then secured with safety wire at the ends. The water boils off quickly during start-up, if the wrap hasn't completely air dried by then.

Drivetrain Installed + Oil Catch Can/Breather Install

The re-installation of the engine is pretty boring work, but it does eat up time. And like everything else, doing this work on a Corvette is more cumbersome than most cars. The ZF6 speed was pressure washed and cleaned up (previously covered in oil from the old RMS leak) before it was bolted to the motor. Everything we touch on a race car goes on clean, even old OEM parts. Dirty parts help hide leaks, cracks and other issues.

Assembling the triple disc clutch to the flywheel, stabbing the transmission and hydraulic TOB, and getting everything into the car was handled by Ryan and Brad. It takes more time to line up the clutch plates and get all 6 pieces lined up together, but this is not hard for our crew. A metal clutch alignment tool is a must for these multi-disc clutches, by the way - we use an old T56 input shaft.

After the drivetrain is in place, the big aluminum C-channel that connects the diff to the transmission goes in (which also functions as the transmission mount, just like on a Miata), as well as the stock aluminum driveshaft. Then the OEM exhaust system goes in, the stock shifter is installed, various wiring harness plugs are attached, etc. No pics of that as Brad was helping and I was across town. This car still has the original OEM mufflers and catalysts, which we visually inspected very closely before the motor went in - the catalyst matrix is still intact after all these years, somehow. Changing the manifolds, cats, mufflers or even the tail pipes costs points in TT-letter classes, so it all has to stay bone stock.

After the engine was in place, we did one more (zero points) upgrade I had planned on for a while, and one we do in a lot of customer's race cars (see above) - add an oil catch-can/crankcase breather. This is something smart to add to any car that sees track time or extended RPM use. The way we plumb these, and how we specify the catch can itself, depends on if its an emissions legal street car (above right) or a track-only race car (above left). A street car isn't supposed to have an open vent for crankcase fuel/oil vapors to get out to the atmosphere, so street driven cars are plumbed with a PCV system to pull excess crankcase vapors out during deceleration and route them back into the intake manifold, to burn them in the engine. Liquid oil in the crankcase vapors is trapped within media inside the catch can, which can collect in the can and be drained out after track days. On a race car you don't have to do with a PCV system - and you don't want to.

This is how much smoke was coming out before the engine rebuild... that's all blow-by

One of the main problems we had with the LT1 motor in the Corvette earlier this year was tons of blow-by. Combustion by-products getting past the piston rings and valve guides/seals then pushed into the crankcase. This was only realized after the leaking oil pan gasket and rear main seal were fixed before our second 2015 NASA event in this car. The blow-by was from worn out rings, three valve guides that had lots of play, and valve seals that had crumbled over two and a half decades. It was smoking so badly we couldn't make one lap without being black flagged.

This is the Peterson 08-400 catch can / breather tank we used

Since I didn't want to take any chances after having "that smoking Corvette" for two NASA race weekends this year, I ponied up for a Peterson Oil Catch Can / Breather a few weeks earlier. It has two -12 AN fittings for inlet, a -6 for a drain (which comes plugged), and the built in breather in the cap. Even comes with a nice mounting clamp. So when the motor was back in the engine bay Ryan and Brad mounted the breather can on the firewall, then plumbed some -10AN bulkhead fittings to both valve covers (because that's what fit the OEM hole on the passenger valve cover).

One fitting went in the factory PCV suction line on the passenger valve cover but the driver's side cover had to be drilled. We have removed the PCV valve and function completely. These factory LT1 "center bolt "valve covers are magnesium and tricky to work with, but they were drilled handled properly and plumbed with -12 sized push-lock 300 psi hose and -12 AN fittings into the Peterson tank.

Now both valve covers vent will excess crankcase pressure to this oil catch can, without the need for a vacuum source to "pull" the vapors out. This Peterson catch can has an integral breather in the lid, which is what makes it not street legal. We have completely done away with the PCV system, so now it is less troublesome and won't allow oil and/or unburnt fuel vapors to be returned to the intake track to be burned - which can cause detonation. And if you get a lot of blow-by it won't send liquid oil back into the intake, which is really bad.

First Fire + Weird Ignition System Issues?

After the breather tank was plumbed, all of the engine fluids were topped off and some Royal Purple break in additive (zinc) was added to the 10W40 Mobil1 synthetic oil we used for initial break in (normally I like to run 15W50 in race cars). The ignition coil and the fuel pump relay were disconnected, then the engine cranked for 10 seconds, and it made 20+ psi of oil pressure almost immediately. After that the coil and fuel pump were hooked back up, the fuel pump was triggered a few times (key on/off... on/off.... on/off) to prime the fuel pressure in the lines and fuel rails, and then it was cranked. And cranked. And nothing. No start.

Then began a full day chasing the starting problems. First we assumed the obvious: it was Optispark related. This is the name for the system GM tried (and failed) at making a better distributor with in the GenII V8s, with a weird unit is driven off the timing gear at the front of the motor. This is widely known as a problematic system. The GenIIs camshaft drives the water pump, also strange, which feeds the motor with coolant in the reverse order of any other motor on the planet. The water pump is right in front of the Optispark, and if any coolant/water gets in the Opti, it usually dies. The LT1's two main bad ideas were the Optispark and reverse flow cooling - they were both abandoned in the next generation engines by GM (GenIII LS1).

Checking fuel pressure, computer issues, wiring harness breaks at Vorshlag (left) and True Street (right)

The other issue we kept running into was thought to be VATS related, or Vehicle Anti Theft System. There's a chip in the ignition key that tells the computer "Hey, I'm legit!". Without that handshake the fuel pump won't fire. It intermittently worked, so we have to disconnect the battery to clear it up. Something I thought was removed when True Street tuned the car, but the SECURITY light kept flashing. The VATS on my 1999 GMC truck was doing the same random faults a few months ago and Sean from True Street plugged in and turned that mess off, too. GM "VATS" is pretty much a "leave me stranded in my own car" system.

The Optispark previously used in this C4 was an aftermarket $500 MSD unit that had less than 3 hours of use on it, so I doubted it could be bad. Maybe a ground wire was missed, or a wire cracked during the install (from age) on the factory harness? Ryan and Brad broke out the factory 1992 Corvette manuals and went through the Ignition Troubleshooting Flow Chart, step by step. Everything they checked worked, we just didn't have spark. Voltages were checked in the harness and into the Opti at several locations. The coil was swapped out for an MSD LT1 unit we had in the shop. No help.

continued below
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16 Oct 2015 06:02 PM
continued from above

Finally we broke down and ordered a stock replacement $150 Optispark unit from O'Reilys, which showed up 10 minutes later. It was 3 pm the day before our scheduled dyno day and track test, so it was worth the peace of mind.

This small victory was short lived - the problem never really was in the Optispark

We plugged the new unit into the engine harness, put the coil lead near the cylinder head, and spun the drive on the Opti... pop-pop-pop. We had spark, so it was proven to work. So out came the nearly brand new MSD Optispark unit, which meant the water pump we had just installed had to come back off. Order more gaskets while that's being swapped in. While the MSD Opti it was off the car they did the same "off the car" test and... damn it, the MSD unit worked like this, too. So I had to make the call... put the problematic MSD unit back on or have them install the brand new OEM replacement Opti? I told them go with the brand new unit.

By this point we had called and spoken to several LT1 experts and got suggestions from "bad ground", "bad ignition module", "bad ECM" and of course "Its the Opti!" It is almost always the Opti, but I doubted that more and more as we tested the old MSD unit off the car and it came back as good.

Another short lived victory - it started with the new Opti, but ran poorly

After a long day of troubleshooting the engine and with the new Opti installed, the engine fired up and ran briefly with the water pump off, so that was good. Then the water pump and coolant hoses had to go back on, the coolant get filled (with distilled water + Redline water wetter) and burped again, and the front of the engine went back together - drive belt, intake tube, etc.

What should have taken an hour to wrap up that Thursday morning ended up taking all damned day. The engine was finally started, it ran (poorly), the coolant system burped, temps checked out and loaded into the trailer for a dyno test the next morning. It was 7 pm and everyone was glad to go home.

Still, it just wasn't running that smoothly. The engine was idling way too high, way up at 2000 rpms, and it had a throttle tip in stumble. Our LT1-expert Ed stopped by and got the set-screw on the throttle blade set to turn ever so slightly and now it would idle at 1600 rpms, but it wouldn't go lower. Hmm. Also, after the engine warmed up, it wouldn't start again easily. It would crank, but wouldn't fire. Something still wasn't right. After 10-15 minutes of cooling down (it barely got up to operating temps) it would fire up, but once it was warm again and we shut it off, then tried to restart it - nothing. Just cranked, no fire. What is going on here? We scoured the car looking for other issues - grounds, broken wires, etc.

The guys at True Street had been ready for us to come by mid-day Friday for a dyno check and re-tune, but with the Optispark + other issues, we were delayed by several hours and missed their deadline. I called them at 4 pm and told them we were going to miss that window. Luckily they were hosting a big "dyno day" setup the next morning, so I planned to get there early and be first in line.... then head to ECR for a member day track test right after that.

Dyno Check at True Street, Saturday October 10, 2015

Loading the car into the trailer with a triple disc clutch is a PITA, but we hadn't stopped long enough to make front (or rear) tow hooks for this car. So when we got to True Street Motorsports at 8 am Saturday morning, an hour before they opened, Amy and I just rolled the car out of the trailer. Then I tried to start it...

NOPE. It cranked like a champ, but once again the coil wasn't firing. It won't start now, even cold. We fought with it for a solid hour, clearing the battery and trying again and again. It got to where the battery was losing voltage, and it still wasn't starting.

I thought about asking the guys at True Street for a hand, but they were all busy getting their shop cleaned up and ready for 200+ people, who had started arriving in droves. They had a food truck setting up, and cars starting to get dyno'd when we decided to abort the dyno test and load up.

Missing this open track day at ECR was a huge disappointment, and it put me in a foul mood for the rest of the day. I knew we would have to spend more (unbillable) hours the next week to get the C4 running "right" and starting consistently before going to NASA @ TWS the following weekend, without any test time on track. With a new motor, new radiator, and new crankcase breather. Testing this many new things during a competition weekend sounded like a bad idea, and it is.

More Testing At The Shop + True Street

Monday morning we unloaded the Corvette at Vorshlag again and Ryan and Brad spent most of the day tracing circuits and testing everything, wiggling the harness, and looking up issues with these cars. More and more evidence started to point to a bad ECM - the 25 year old engine computer might be at fault. My ops manager Steve started chasing down replacement 92 Corvette ECMs and that search went well into Tuesday. He called dozens of wrecking yards and LT1 re-programmers, parts suppliers and GM dealerships across the country. Nothing, nada, zip.

Sometime around mid-day Ryan had done some sleuthing online and found a number of 92 Corvette owners with eerily similar problems. One suggestion was to remove the PROM chip inside the ECM housing and re-seat it. Another said to "whack the ECM a few times, hard!" After doing those two things the car started up again, but still ran a bit rough. More tests were done, but it at least ran. We called True Street, who were backed up with tuning work for 3 weeks... I begged, and they agreed to call me back if they had an opening. As luck would have it they had a last minute cancellation and were able to sneak us in for a dyno check-up. I towed the C4 up there Tuesday after lunch and they got to work.

After I left, it wouldn't start again. Sean played with things, checked some codes, and late that day they had found a bad TPS sensor. With the TPS unhooked it would start, but you can't drive the car like this. We had replaced the TPS with a new sensor back in February, after I noticed a weird "throttle dead spot" at the January NASA event. Hmm... red flags were going up.

I spoke with Paul Costas later that night and told him the symptoms we were having, and he related a similar issue he had on his 92 Camaro (which is a GenI TPI V8, but used a similar vintage computer and EFI tech). About a year ago 92 started running poorly and burning up TPS sensors. He talked to an EFI expert familiar with this vintage GM EFI hardware, who said when these ECMs go bad they often lose their reference voltage outputs for 5V circuits like the TPS (Throttle Position Sensor) and IAC (Idle Air Control). He told Paul to test voltage signal at the TPS while driving... and sure enough it spiked way above 5 volts several times, which was what was burning up the sensors.

And we've just burned up another TPS sensor, and the car had a weird throttle response issue when it would run. And the idle was super high (IAC circuit) at some points. I was more convinced than ever that the ECM was dying and emitting some weird reference voltages. But with no replacement ECM for this car to be found nationwide, the chances of making TWS looked slimmer by the hour.

I was stewing over this for days and mid-day Wednesday I decided to scrub the TWS event. We had ECM problems and there was no way to fix it in 24 hours we had left. Crap, crap, crap!

What's Next?

Long term plans had always been to convert the car to a different ECM and harness from a later 1993-96 Base Trim Level Corvette. There were some EFI changes through the 1992-96 LT1 Corvette era which included:
  • 1992 was the first year of the TL1, speed density air metering, and had the weakest computer with the least number programmable inputs
  • 1993 was still speed density but had a more powerful computer with more inputs to alter
  • 1994-95 was another step up in inputs and computing power with the added change of a move to Mass Air Metering, but still OBD-I. Yet these can be reprogrammed via the OBD-I port, no more E-PROMS.
  • 1996 was another big change, such as the move to OBD-II standards, the ECM had a significantly more powerful processor, a LOT more data channels and programmable inputs, and also no longer relied on an E-PROM to change programming.

Checking with all of the parts suppliers we use it appears that new AC Delco ECMs for the 1996 Corvette are readily available, and around $200 (with the core charge). The other years are "iffy" or just downright impossible to come up with reliable units. So it looks like I am going to be chasing down a good 1996 LT1 Corvette engine harness, ECM, Mass Air Sensor, and intake tube next. We could not hope to pull this off in the one day we had remaining before TWS, so that event had to be scrubbed.

We had ordered new R7 Hoosiers, procured a 2nd set of wheels (for the scrub set of tires), event fees were paid, Amy had taken off work, arrangements for the weekend were set, and lots of money thrown at ignition parts that weren't bad - but hey, "that's racing."

Some of you might question scrubbing this 3 day race weekend - since the engine "technically starts" now. Sure, you can unhook the TPS and it might start, but it cannot be driven like this in anger. It is not reliable, and will almost certain break and/or run poorly once we get this thing on track. If we plug in the TPS it will burn that sensor up in short order.

I'm not giving up on this car, and it will likely be run in 2016 up until our "Shop Car" LSx BMW is complete. So look for us at NASA events in January and more likely some TEST EVENTS before then, to verify the new engine and ECM changes we have in store. My next update will be after we make the wiring harness and ECM changes.

Terry Fair @ Vorshlag Motorsports
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05 Jan 2016 03:16 PM
Project Update for January 5th, 2015: Its been a couple of months since I touched base on the progress of Project #DangerZone, our 1992 Corvette race car, and a lot of little things have happened - both to the car and to the NASA base classing rules for 1992-96 Corvettes. We've made some updates to the C4 to hopefully make it lighter (pre-ballast), run cooler, and more importantly - be more reliable once it returns to track use later this month. The C4 is also looking like my only primary race car for 2016, so we're getting a bit more serious with prep on this car and might add a few other racing groups to run the car in. There's only 3 weeks until the next NASA race we want to make in this car (NASA @ MSR-Houston event Jan 23-24) plus a test day at MSR-Cresson the weekend before (Jan 16th at MSR-C). I'm only going to cover the work completed up until now then catch up on the finish work before these two race dates in the next update.


As some of you might know we've started a BMW E46 330Ci build for NASA TTD class. That project has gobbled up some time and we switched chassis before we even began major race prep on the first car (325iC), which slowed us down a bit, but it was the right move going from the 325 to a 330 (the latter of which was classed better and makes a lot more power). You can read up on that car here, which we've named Project #JackDaniels. I explain the name in that thread.

Normally in December of each year, NASA will release an updated rule set for Performance Touring, Super Touring, and Time Trial classes - all 3 of these groups use essentially the same set of rules. PTB-PTF wheel to wheel classes equate to TTB-TTF and ST1/2/3/U equate to TT1/2/3/U. Sometimes the rules aren't published until after the first of the year but this time the 2016 NASA TT rules came out on time, with nearly 8 weeks before our January 2016 event.

The C4 listings above are what we built this car around, and those haven't changed in many years (we know because we have been eyeing this car for TTC for 4+ years). But due to how well Dave Schotz did at NASA Nationals West in his PTC/TTC C4, and how much we riled up a few folks with our forum build thread (even though it really only completed one race weekend), we were expecting either a points penalty (*), class change (TTB?) and/or minimum weight change (increase) to these C4 base classes. So here are the 2016 changes...

All changes from the previous edition of the rules this year are shown in blue. As you can see the minimum weights for 3 of the C4 models were changed, all higher, including our 1992 LT1 base model. We have to add 57 pounds to our weight or else take points for weight loss, which gets expensive. As you may know we had maxed out this build on points from the beginning. Somehow I never really covered that in this thread...

This post on our E46 TTD build thread explained in great detail how we came up with the classing, tire size/compound, chose modifiers and found rules exploits for both the TTD car and this TTC car. I won't repeat what I wrote there in total but if you care to learn some of our secrets, please go here and check it out.

Here is a quick summary of our TTC class build for this 1992 Corvette, based on the old 2015 rules. After we saw the base classing (TTC*) and weights we looked at the Power-to-Weight (P-to-W) ratio assigned to the class (12:1). The * cost us 7 of the 19 class points we had to spend, so we have 12 to play with to stay in TTC. Then we looked at the base tire assigned to the class (255mm). Going up in size costs points, down in sizes nets points back. From there we looked for modifiers to the P-to-W ratio... and found a big bonus (+0.8 ) if we ran a small 245mm or smaller DOT tire (see Appendix B in the rules). 1 point was also gained back because that's 10mm below the TTC class starting tire size of 255mm.

This modifier effectively moved the P-to-W from 12.0:1 to 11.2:1. Luckily the stock LT1 motor could still hit that revised P-to-W limit without any power modifications. This meant we didn't have to burn class points on exhaust or headers or camshaft swaps or intake mods to max out P-to-W. We spent ALL of our remaining points on suspension changes (springs at +3 points) and tire compound (R7, +10 points), plus our point gained back for 245s (-1) and it worked out to the 12 point mod limit for TTC with maxed out power limit.

Let's show those P-to-W calcs "the NASA way" for our TTC Corvette:
  • Weight must be at or above the listed minimum classing weight of 3203 pounds, from the 2015 rules
  • That 3203 number is also just above the minimum "competition weight" modifier numbers, which start at 3200 pounds
  • We chose a 245mm width DOT legal tire (+0.8 P-to-W bonus)
  • The stock engine made 284 whp peak (highest of 3 pulls)
  • 3203 lbs / 284 whp = 11.28:1 (P-to-W) + 0.8 for (245 tire modifier) = 12.08:1

TTC Class "minimum" adjusted P-to-W is 12.0:1, which this car is just a hair over. That's what you want to do - aim for the P-to-W limit and find any modifiers you can to help that ratio along the way. Avoid modifiers that hurt, then use your points to run the best tire compound/width and fix any suspension issues, and add aero if you have any points left. Again, this is more detailed in the E46 TTD thread, linked above.

So that was our TTC strategy for this C4. Now we have to recalculate for the higher 2016 minimum weight bumps, which honestly aren't that bad and are not unexpected. I have to agree with these changes, even if I don't like them. This will mean we have to run even more ballast on the same 245mm tires, which worries me. We haven't dyno'd the fresh LT1 motor but I'm also worried it might make too much power, even at this higher weight (and with the 11.2:1 P-to-W ratio we can now make 291 whp). Even with it only running briefly due to the ECM issues it felt STRONG - and yes, it was a 100% legal engine rebuild. We shall see soon enough.

Sadly our E46 TTD build gained a 7 point penalty with the 2016 rules, which I'm not at all happy about. Really borks the planned build. So of the very few changes made in 2016 both of our TT-Letter builds were impacted. I'm just that lucky, I guess.


Meanwhile in last two months, before we got the new 2016 rules, we have been working on some reliability mods to the C4. Of the 2 race weekends we ran this car I never managed to make more than 2 laps in a row. So the stock Z51 brakes haven't been pushed hard enough to overheat, but I'm worried they will be taxed once we get the car on track without a leaking or smoking engine. Why worry? Well because I'm a Left Foot Brake fanatic (learned in my autocross background) and I tend to abuse the crap out of brakes.

With an R7 tire compound I don't have to get my best laps in on lap 1 or 2 like we did on the A7s in TT3 last year, so yea... brakes might become an issue. So one day when we had the C4 up in the air for harness removal (see below), I asked Olof to pull apart the front brakes on one corner for a better look. We had built brake backing plates with cooling ducts for a C4 before and he kept the templates we used that time, so this shouldn't be a whole lot of work.

After he made a flat plate that fit around the hub we discussed where to route the hoses, what sizes to go with, and what shape for the duct at the backing plate. We decided to use 3" oval tube for the inlet, aimed at the hub and inside the rotor face. He built these 2-piece backing plates below.

With only a 13" rotor there wasn't room for a 4" duct, and with the track performance of this car a 3" cooling hose should be enough. Now there's also lower piece to this backing plate added to help seal off the hub section so that the incoming air goes where we want it to. It also allows for a bit of a heat shield from a ball joint that is very near the inside rotor face, shown below.

The spacing from the backing plate to the rotor face (shown in the picture above right) is what we try to stick with, which allows a decent seal to the incoming air but shouldn't ever rub. The goal is to turn the rotor into a centrifugal air pump, with the incoming air forced into the hub area inside the rotor and the curved vanes of the rotor pulling air through the rotor and out radially. This can increase effective braking during a session considerably, as well as extend brake pad and rotor life substantially.

As you can see above left, even the oval shaped 3" duct doesn't put the incoming air completely inside the rotor face, but its as close as we can get without nearly flattening the oval shape. Another thing that we did while the hubs were off was install extended length 3.25" ARP wheel studs. We couldn't find a bullet nosed ARP stud any longer than the itty-bitty stock studs, so we'll just have to start each lug by hand with this fully threaded ARP (it's not like we're doing fast pit stops). The reason why I wanted long wheel studs will make itself known in my next post.

While doing the front stud install we would normally swap in new hubs at the same time, for other cars. But for the C4 we kept the original front hubs - they were still low mileage, still felt tight, and the aftermarket options are total CRAP for this chassis. The only good aftermarket replacement hub for this car worth using is a racing hub made by HPE that costs $699 per corner, and I'm not sure if their solution is even TTC legal, so we'll keep the stockers on there for as long as we can. Brake cooling aimed at the hubs tends to extend their lifespan quite a bit on track, too.

Backing plates are only 1/3rd of the brake cooling solution - you also need INLET ducting at the front of the car and then brake hoses to join them. After looking at the front end of this C4 I wanted Olof to "keep it simple". Why? Well we're likely replacing the bumper cover later in the 2016 season since the stock cover is pretty beat up. We had discussed about re-purposing the turn signals, adding NACA ducts in the old headlight doors, or even NACA ducts under the front bumper... but I wanted to keep it very simple. "Just make a 3 inch round tube and a flange", which is exactly what he did.

Remember - this might not be the permanent inlet duct solution, just a quick one for now. The inlet ducts were relatively easy to make and I had a specific place I wanted them placed. The front of the C4 has a LOT of "front overhang" (see above) where the nose pokes out about a foot in front of the factory front lower air dam (the air dam feeds air to the radiator). All of the radiator cooling is drawn in from under the giant overhang, but there is still some dead space on both sides of the radiator inlet that goes unused...

continued below
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05 Jan 2016 03:17 PM
continued from above

That's where I had Olof place the inlet ducts. "Just drill a 3 inch hole and bolt them in right there", I told him. The inlets are directly underneath the factory headlight holes, taking in high pressure trapped under the nose that isn't being fed to the radiator inlet. There's ample room under the hood (with the flip-up headlight assemblies gone) to route the hoses up and over to the brake backing plates.

Due to concerns Jason and I both had about air pressure bleeding off laterally towards the edge of the nose and bypassing this brake cooling inlet, I had Olof make a little aluminum "brake canard". This is a little air dam that forces some air into a closed pocket to feed the brake inlet. Yes, I know this might incur some aero penalty for TTC. We are going to test with and without these in place and we will add rivnuts in place of the rivets used to attach these little air walls, so we can test with and without them installed.

The brake hose routing looks fairly straightforward, but of course we haven't tested it on track yet. It might rub the wheel at full lock, but since the car is still in the air with the wheels off we haven't checked that yet. A piece of the plastic inner fender liner was trimmed to route the 3" hose below the top of the wheel, but we will see how it fits when the wheels and tires are mounted and its back on the ground.

Last but not least the car is getting a new set of factory lower air dam plastics. Again, we bought these many months ago just never got around to it. The old bits are beat up and the left sides is held on with Gorilla snot and is half falling off. The new air dam bits will help push more air into the waiting duct for the radiator or the two brake inlet ducts.


Another piece I had purchased way back in January of 2015 that never made its way onto DangerZone was a pre-formed and pre-cut polycarbonate rear hatch from Five Star Bodies. This 1/8" thick, pre-trimmed, formed rear plastic glass was to replace the 46 pound OEM glass rear hatch section.

Removing weight was the primary goal, but with our new 2016 minimum weight numbers going up now this might not make as much sense.

Of course we did this before the new weight numbers came out, heh. Oh well, being able to move weight from up HIGH (stock glass) to down LOW (ballast) is always a good thing. I'm eyeing that 80 pound hood as well.

Once the glass was removed from the factory hinge at the back of the B-pillar factory roof structure, Olof drilled two matching holes in the trimmed-to-fit and pre-bent Plexiglass. Then he built a frame to give it some support at the lower front corners out of thin wall 1/2" tubing. The two Quik-Latches just arrived and those will take the place of the (broken) rear hatch release. Now we can get into the rear area without crawling through the cage and yanking the emergency release cable in the back.


So if you've read this thread before you know we had some trouble with the original 1992 ECM (Engine Control Module, or computer) after the rebuilt motor went in, that caused us to miss our last NASA race of the year - the car wouldn't start reliably. After days of diagnosis and parts chasing we had finally realized it was a bad ECM. Well we cannot find a new 1992 ECM, anywhere on the planet. 1992 Corvettes had a "one year" ECM - 93 was different, 94-95 was different again, and 96 was also unique. There are no 1993 ECMs left either, but back in October we found plenty of 94-95 Corvette computers available, both new and rebuilt, and our tuner said the later computers were easier to tune for track use. So the quest to convert this to a 1994-95 EFI harness was underway in October.

Instead of trolling junkyards for 20+ year old Corvette engine harnesses, which will bound to have some cracks and wiring breaks, we had a new one built using our 1992 OEM wiring harness for layout. We found several breaks in the existing 1992 harness already - which makes for nightmares when diagnosing EFI issues and the way this one will be built will be the perfect OEM replacement - 100% stock in form and function, just not with 25 year old wiring and broken connectors.

We had to find 1994-95 MAF, intake tube and other small parts to convert this car fully

We are trying out a new harness supplier, but they assured us it will be identical to an OEM 1995 Corvette harness and plug in, no issues. As long as it mimics the OEM harness and we use an OEM 1994 or 1995 ECM, this should be a zero-point change, as all 1992-1996 LT1 Corvettes are listed on the same line.

The harness took a few hours to label the connectors (any emissions or cruise control related connectors will be removed, which again, is legal for TT-Letter) and disconnect everything all the way to the ECM and firewall, and even some bits that went down to the ZF 6-speed. We should hopefully see the replacement harness by the end of this week, which will give us just one week to get the engine dyno-tuned again before an upcoming track test at MSR-C on January 16th.

That's what the engine bay looks like now, above left. The 1992 harness was been shipped off weeks ago (they have to re-use some connectors, which are not being made any longer) and it will look like the 1994-95 engine bay soon (above right). We already have an OEM replacement MAF and intake tubes, shown there. Luckily this 1994-95 stuff is available and not costly (new Delphi MAF was about $100).

I will show this all wrapped up and hopefully running well again in my next post.


Since this was only a partial update I'll have another that will show the completion of all of the above work (hopefully) posted after the next NASA event. That assumes a lot of things happen in a timely fashion over the next 2 weeks and that our test at an SCCA Club Trials event goes off without a hitch.

Sadly these were the only two tracks we ran the Corvette at last year, but we'll be hitting them back-to-back weekends in January 2016. This time the car will have a newly rebuilt engine, no fluid leaks, better engine and brake cooling, and hopefully some reliability. There were major issues with the C4 at both tracks in 2015 - a leaking rear seal at MSR-H kept us to 1-2 lap stints before we were black flagged, and oil smoke from a worn out engine kept getting the car black flagged at MSR-C in one lap or less. No more of that nonsense!

We ran a 1:43.7 lap at MSR-H in 2015 (still the TTC track record) and hope to better that by a good margin this year. We never got an official time in TT at the MSR-C event but, but I did run a 1:25.0 in the TT Warm-up session, which was my only complete lap of the weekend in that car. That was 2 seconds faster than the old TTC record at the time, but another TTC car reset the record on Sunday to a 1:24.424 (Mark Schnoerr's E36 M3). Hopefully #DangerZone can go quicker than those times at both tracks? The SCCA Club Trials event doesn't really have "classes", per se, but it will be a good practice for when NASA comes back to this track in March 12-13, 2016.

That's all we have planned so far for the 2016 season - after the January SCCA and NASA track events we will see how we stack up in class for the year and go forward from there, either with refinement or possibly even changes to move to a new class (if the added TTC weight is a big hindrance). We will also have Amy's red 2001 BMW 330Ci at these two events, which is the new #JackDaniels TTD classed E46. For the C4 we have to have the rebuilt harness installed with a 1994-95 ECM (of course now there are none to be had, ugh!), the engine re-tuned to work with the 94-95 MAF, the Plexiglass rear hatch painted and latched, the front brake ducting wrapped up, and maybe some other small changes if there is time. Check back in a few weeks to see if some what happens...

Terry Fair - www.vorshlag.com
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25 Jan 2016 03:48 PM
Project Update for January 22nd, 2016: Well the C4 has logged a successful test track day in 2016, where we tested a lot of big and small updates to this car (and a new BMW we're running in TTD this year). There was one fairly big change with Project #Dangerzone that we have been holding back - because, honestly, I didn't know if it would work. I will explain "the what, why and how" below. We also finished lots of little prep work to this car, installed the rebuilt wiring harness and 1995 ECM + MAF, got the stock rebuilt engine dyno'd (twice), added some tow hooks, fixed the front air dam, finished the brake cooling and rear Plexiglass hatch, lost some weight, and more.

After my last thread update I was posting the above pictures on social media with captions like "almost finished" or "finally track ready". This was somewhat of a disinformation campaign, which might help me if I ever run for president, hehe. Gotta keep you guys guessing a little, but the big reveal is shown below. Let's get caught up...


In my last update I showed the slightly unfinished work on the lightweight polycarbonate rear hatch replacement. Shortly after I wrote that, our guys got it painted and installed and it looks good.

The rear frame was made from thin wall 1/2" steel tubing, which is tricky to bend. This structure forms a frame that wraps around the back glass in 3 axis. Olof welded some tabs in place for the small diameter Quik-Latches that secure the bottom of the hinged rear glass, as well as tabs for the hinge mounts at the top.

The mating pins for the Quik-Latch kits were installed in some simple brackets that Olof built and attached inside the rear of the hatch opening. Not only did the heavy 46 pound glass go away the big, electric solenoid operated, clunky steel latch mechanism also went away. The optional spring kits were added to the QuikLatches and that made them work a lot better. The rear frame was painted while hanging on a rack, and I snapped the pic in front of the LS1 Miata - which is about to get a big project thread update. We neglected to snap a picture of the final weight of the Plexi hatch and frame, but it looks like we lost 30-ish pounds - the new hatch is super light and much easier to lift.

I had the guys paint the back of the plexi around a ~3" border, to give it an OEM look. Trust me, its worth the time and makes a helluva difference. Brad and Olof taped up and covered the area not to be painted then peeled the protective covering from the inside of the Plexiglass (both sides come covered in a protective film). The clear plastic was scuffed with ScotchBrite then cleaned and let dry. Then it was painted with two light coats of semi-flat black.

The painted hatch was then allowed to dry, after which time the frame was bolted to it on the inside and the QuikLatches installed. The frame was bolted to the factory hinge using the same stainless washers and flush head bolts we use on all Lexan window installs. The latches lined up and the spring poppers were added to the Quik-Latch assemblies.

You have to see it in person but the finished hatch looks really good. Going the extra yard to paint the border (on the inside) makes it look so clean and factory, covers up the steel tubular frame inside, and finishes off this mod well. The Quik Latches work great and we can access the rear hatch easily now (before you had to crawl through the back of the car and pull a cable - total PITA).


Updating the ECM and harness on this 1992 Corvette was the least fun part of this project to date. What a giant hassle, but the old 1992 computer can no longer haunt us, the engine runs now, and we learned a lot about the differences between the 1992-1997 LT1 engines & cars.

Just finding a used 1995 Corvette Engine Control Module proved to be difficult, as all of the sources we saw that had them in stock back in October had dried up. Lots of calls, emails, and finally the guys at True Street told me about a possible source. We paid too much ($315) and its a used ECM (not "reflowed" or rebuilt), but they do program the VIN # into the ECM for us and ... well... they had them in stock. Since it came pre-programmed at least it worked on their bench harness, which is a plus. The VATS would be turned off so the engine could run with our key, too.

You can see how different the 1992 (left) and 1995 (right) ECMs look. This is why we needed to have the harness rebuilt - to fit this entirely different pin-out for the later model ECM.

Here you can see the Delphi replacement MAF (Mass Air Flow) sensor, which is part of the later 1994-96 Corvettes' EFI systems. The online resellers show the same stock replacement part from 1994-2001 Corvettes with prices from "cheap" to "not as cheap". These sensors have a "hot wire" that sits in the intake airflow path, voltage is applied to this, some wizardry is used, and the amount of airflow is measured more directly. The 1992-93 Corvettes used a "speed density" method of airflow measurement, where intake manifold pressure was used to infer the airflow. The MAF cars still use the old intake manifold pressure sensor, but use that data for fine tuning, not engine airflow measurement.

New intake hose ends were needed on either side of the MAF sensor to connect it to the air box and throttle body. The sharp eyed among you might realize that these are not OEM replacement rubber bellows, so they aren't technically TTC legal without taking 1 point for an aftermarket "cold air". There's a reason why this doesn't matter that will soon become apparent.

Going from the jumbled harness right out of the box at left to the completed and running engine harness install on the right took a few days, mostly chasing down "old car things". First it was the O2 sensors, which are different on the 95 vs the 92 (went to a heated, 4-wire O2 @ $29 each x 2). Then there was the IAC valve changes. The rebuilt harness was setup for the 95 Corvette computer and they updated the ends for all of the 1995 era sensors, too. Cheap, easy fix that will likely work better than the old 2-wire O2 sensors.

Next was the computer itself, which had such a different shape that the (complicated) fiberglass bracket made to hold it was different. So Steve called up a salvage yard in Waco we know that keeps a lot of C4 Corvettes and he got this new bracket for $40, which arrived the next day. Could we have built one? Sure, but the shape and how it mounts was complicated enough that making one would have taken an hour or more, and every hour we're spending on this shop car is an hour we're missing out on customer work. $40 for the factory piece was the right move here. Remember: even though you can make something from scratch, doesn't mean that you always should.

Yet another "learning more about 25 year old LT1 engines" thing here - the Idle Air Control valve (IAC) is an electronically controlled device that meters air around the (closed) throttle blade, so the car can idle with your foot off the throttle pedal. GM changed the mounting shape and the 4-wire connector for the IAC from the 1992-93 LT1 cars to the later 1994-97 LT1 cars. The way the IAC mounts to the throttle body is via a small "manifold" (above right) that bolts underneath. As far as I can tell the throttle body didn't change much, so we just needed this 1994-97 IAC/coolant manifold, which bolted to our 1992 throttle body.

After a full day searching we realized this part wasn't available new, and even Nook & Tranny was out of stock (they carry a lot of LS1 and LT1 stuff - helpful website for engine swappers). It was late in the day when we realized how scarce this manifold would be, and our Waco Corvette salvage yard was closed by then.

So we started looking for LT1 throttle bodies locally... my Facebook call-out was a miss but someone there suggested a junkyard here in town that had one for $50. So the next morning, the highlight of my birthday was trolling around in the bad part of town and grabbing up this 1996 Camaro throttle body. Ryan cleaned up then transferred over the IAC/coolant manifold and the new 1995 Corvette IAC ($53) to the 1992 throttle body and it was ready to fire. Curiously the shape of the throttle blade cable pivot cam was very different from the Camaro to the Corvette parts.


We've not had good tow hooks on this car, which is pretty short sighted for a track-only car. This is one of the first mods usually done to a race car, and we were lucky we never had to be flat towed in at the track, because there's not good places to latch a tow strap onto in this car. The front of this car is all plastic and there's nowhere good to bolt or mount a tow hook, so we had to get creative.

We figured out on a previous C4 race car how well a roll cage mounted top tow hook works, for both winching a car into a trailer as well as for towing behind a wrecker. The top hook eye Ryan added to the cage also works as a great grab handle to winch yourself into the tight cabin of a C4. It will be easier to get into this car once I have sprung for a Quick Release and a real steering wheel, but for now this works great. Have already used this new hook to winch the car into and out of our trailer multiple times.

Ryan also installed this roll cage mount "bus stop" mirror, a low cost convex mirror that lets you see into blind spots. We already have a 14" wide parabolic rear view mirror mounted in the cabin, but the right side factory door mirror broke decades ago, and the FIA cage tube on that side blocks my sight line to it anyway. This new spot mirror fills in the right side visibility gap from the side window to the high mounted rear view mirror perfectly. Bolted on in minutes and the old, dead door mirror housing was removed (less drag).

The guys also got the final routing of the 3" brake duct cooling hoses nailed down. There's a number of zip ties that attach the hoses to moving suspension components, like the upper control arms. And some that hold them to fixed items inside the engine bay.

These hoses even clear the 335mm tires on 18x12" wheels up front at full lock, so they really got them tucked in there nicely. Oh yea... did I forget to mention the little wheel and tire upgrade??


What and why have we changed from the 245 R7 tire to a 335 front and 345 rear Hoosier A6?? Well let me try to explain. And remember, this was only a test - it might have been a complete disaster and I would have un-done the work and slapped the TTC legal 245s right back on.

Last year we only built this Corvette to run for one season as a "tweener car", after the TT3 Mustang was sold and before our next big crazy shop BMW V8 build was ready. Well we never started that big BMW build, which was delayed for multiple reasons. So this old 1992 Corvette was quickly shoved into the "fast shop car" role, with some planning that began last October.

It also didn't make sense (to me) to have both of our shop cars in NASA TT Letter classes - the red BMW E46 330 in TTD and this white C4 Corvette in TTC. That's a little nuts. So back when we were looking at a TTD build for a BMW E46 coupe, we had already decided to move the Corvette out of TTC, or at least test some "big tire theories", with a wheel and tire upgrade to the C4 early in 2016.

I suck at keeping surprises, and not sharing pictures of these wheels when they arrived and were initially tested was killing me. Just the 335 Hoosier tires were mocked up on the front (above) a few months back, but I couldn't share that either. These were some new A7s I had sitting around, winnings from the TT3 Mustang. We have half a dozen sets of scrubs, too.

continued below
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25 Jan 2016 03:49 PM
continued from above

While we started out thinking about just an 18x11" wheel and 315 tire (which would have fit under the stock fenders), the 335s fit so well under the stock fenders we measured the car for 18x12" wheels at both ends and pulled the trigger. 18x11 and 18x12 wheels cost the same, and I didn't have any (free) 315 tires laying around. So the 335/345 tire combo was chosen for... budget reasons??

The easiest way to add a lot of performance to this TTC Corvette, since we had just had the engine rebuilt to painfully stock spec's, was adding mechanical grip. The easiest path I could think of was to add giant wheels and tires and dump some weight. So I started to do some TT1/2/3 calcs for this car late last season and it looked like TT2 would be a good goal. Here are our TT2 goals...
  • Goal Weight: 2850 empty, 3050 with driver
  • Goal P-to-W: 8.0 to 1 (TT2)
  • Goal power: 381 whp
So the 381 whp power goal? Yea, we're not close to that yet, and I will show our dyno tests below with the new motor. We have some things in mind but we figured it was worth testing this theory with the existing ~295 whp power level before we do any mods that could not be "undone", so we had a path back to TTC in mind if the first 2 events in 2016 were a total bust on the big tires.

This 2923 pound weight was with the full cage, 18x12" wheels, and half a tank of fuel. The car is still about 75 pounds too heavy

The TT2 class move was the reason for trying to lower the weight goal - and why we pushed ahead with the plexiglass rear hatch and snatched out the ballast box and multiple 45 pound weight plates. We still have some pounds to go on this 2850 pound goal (without driver), but there are plans to get there. I was just hoping we could get closer to this weight for the first event, and since we got the car down to 2840 pounds back with the 4-point roll bar, small wheels, and no rear hatch before.

If you have read my build threads over the years you know I like to use the biggest wheels and tires that can fit a car, for both road course or autocross use. One of the things our shop is known for is pushing the limits of wheel width under stock fenders on a number of cars: BMW E36, E46, E90, & 1M; EVO X, Subaru GR, S197 Mustang, C5 Corvette, and more. And now we can add C4 Corvette to that list. And maybe.... "fit" is a stretch here, I'll admit. But this car will get some flares soon to make it all look right and cut down on aero drag. We did learn what it takes to stuff a 315 and 18x11" under stock C4 fenders with this test, which is more usable data for most folks' cars.

So as you can see the 18x12" front wheel we spec'd "fits" up front with no mods using the 335/30/18 Hoosier. This could work with zero mods for a street car with 11" wide wheels and a 315/30/18, but we wanted to go for broke so I decided on a 12" wide wheel and 335 tire up front. Again, we had so many sets of 335s and 345s from before. This worked so well up front on a 3600 pound TT3 Mustang that I figured it would work as well or better on a 2850 pound TT2 Corvette.

The rear has an even bigger tire, the massive 345/35/18 Hoosier A7, used on an identical 18x12" wheel as the front. Yes, this tire should used a wider wheel, like a 13" or even 14" wide wheel. But the CF5 and F14 wheels from Forgestar top out at 12" widths in their 1-piece wheels. We wanted a less expensive set ($360/each) of wheels for this initial "big tire test", so we went with the same widths we used on the TT3 Mustang (18x12" front and rear). As you can see in the image above, the 18x12" wheel works with the 345 Hoosier... but it does have a hint of a squeeze. This is a 13.8" wide tire.

This was the fun "lets bolt the front on" test, before we had the wheels powder coated. Just one front 335 tire, tested quick, looked good. Dismount, take to the powder coater, and wait 6 days... Always waiting.


Back on January 14th, the crew here at Vorshlag had finally installed the rebuilt wiring harness (after 3 days of chasing down "changes") and the engine would crank and run... for 2 seconds. The folks who sold us the "1995 Corvette ECM" were supposed to turn off the security system in the computer (VATS), since our 1992 Corvette's key would be coded differently than the used ECM they sent us. They charged us a pretty penny ($315) for a used ECM, but part of that was "installing your VIN # and turning off VATS", and they were one of only a handful of shops that said they had a manual trans 1995 Corvette ECM in stock, too.

Well of course that was bull. It was not in fact a Corvette ECM, but instead a 1994-95 Caprice or Camaro LT1 ECM, made for an automatic transmission. And they left the VATS system on, which was why the car won't run more than 2 seconds. But luckily the guys at True Street Motorsports know LT1s and using LT1edit they were able to convert the ECM to a 1995 Corvette manual trans unit with a reflash. They also reset the speedometer to work with the 345 tire we were going to use (not on the car at this point).

The True Street guys fought with the ALDL port (the OBD port) for 5+ hours, calling the new wiring harness supplier (who I will never use again) and attempted some trouble shooting - since this port now didn't work. It worked before with the 1992 harness, but the $1000 custom built, 1992-to-1995 engine conversion harness they supplied seemed to have nothing but problems.

True Street had to overnight the LT1 "bench harness" for this style ECM, and remove the 1995 ECM from the car for each tuning iteration. With no ALDL port they couldn't data log during a tune, either, which made it even more difficult. The Corvette was stuck at their shop for 2 days and my tuning bill reflected the added work they spent chasing the harness problems. Oh well, live and learn... next time I'll use my standard "stand alone" wiring harness supplier and just punk on the factory gauges. We still lost the factory oil temp connection with this new harness, which is something I really wanted to be able to monitor.

Once the ECM was reflashed well enough where they could make a pull on the dyno, the ignition was apparently breaking up above 4500 rpm. You can see the jagged red dyno curve above, which is with the refreshed LT1 and 1995 ECM + MAF. This curve was beating the old stock LT1 and 1992 ECM tune (in blue) by 25 ft-lbs all the way to 4000 rpms, then it started to tank, then the curve went berserk at 4500.

Both of those dyno graphs are uncorrected, and the "301 whp" line was actually the "284 whp", once SAE corrected. Which is the tune we ran at the 2 NASA events last year. The newly refreshed but still painfully stock LT1 engine was pulling strong in the lower revs, but something wasn't right up top. Over 4500 rpms it wouldn't run. By this time it was nearly 2 pm on Friday, the day before the MSR event. I had to take it like it was, hope it was just an Optispark or spark plug problem, and see if we could fix it back at Vorshlag. I loaded up the car quickly and blasted back to the shop. We hadn't even fit the rear wheels yet and we had another car (BMW E46) to finish, too. Rough, nerve wracking day.

As I raced back to the shop with the trailer full of Corvette, and I called our shop manager Brad and had him order spark plugs and water pump gaskets to be there in a few minutes. We unloaded the car and immediately started yanking the brand new OEM style Optispark, which was installed back in October when we were chasing the bad 1992 ECM problem. It was a vented, name brand, brand new unit with 0 miles on it. How could it be bad??

Ryan swapped the nearly brand new spark plugs for a fresh set of NGK V-power plugs, and I had hoped one of the old plugs had a visibly broken tip or insulator (which would explain the dyno issue). Nope. The MSD billet Optispark distributor was pulled off in October, but it wasn't the problem, so now it went back on. Ryan and Brad thrashed with this while Olof and I worked on cutting the rear fenders to clear the 345s (see below) and Jon and Steve finished up the BMW 330 prep. It was an "all hands on deck" kind of afternoon.

The old MSD unit went in, the water pump went back on, the cooling system was refilled with distilled water and a splash of Redline water wetter, the engine was run, and the cooling system burped. Moments later we were cutting the front fenders and by 7 pm the car was loaded into the trailer. Fingers were crossed - there was no way to "feel" the ignition flutter until it was in 3rd or 4th gear, and it was pitch dark outside. I was not going to go blasting down the road with no lights to test this. We'd have to see if the MSD Opti fixed the 4500+ rpm issue the next day on track at MSR... if it didn't rain. Or snow. The weather was beautiful on this Friday, but predictions of COLD, wind, snow and rain were in the forecast for the next day. Yay. And MSR-Houston NASA event was the next weekend, 5 hours away... we needed to test the engine right NOW.


While the Optispark was going in, after the car returned from True Street on Friday, all four of the 18x12" wheels and a scrub set of 335F/345R tires were fitted to the C4. The fronts looked a little close to the hood for bump travel and the rears poked out a mile. Time to cut some fiberglass.

Making the rears fit took a bit of fiberglass removal. First we laid down some green painters tape then I marked an "eyebrow cut" line, to give the rear some bump travel. At this point the tires stuck out about 1/2" but we would later see that we needed more like an inch of poke. Again, this is an identical 18x12" wheel as the front, and we planned up front to use a bit of spacer to make it fit out back. Long term, these 18x12's might all become front wheels, then we'll get the new M14.2 Forgestar 2-piece wheels out back in 18x13".

Fiberglass dust is nasty stuff so we had Brad cutting and me or Olof with the vacuum sucking up the dust, and dust masks. Below right is the initial fit, then I went back with a 2" sanding disc and cleaned up the wheel arch a bit.

The front wheel openings were also trimmed, very quickly. There was another "eyebrow cut" at the hood-to-wheel arch portion, just above the tire, to allow for bump travel. This happened right after an Optispark change was finished.

That's how it was loaded into the trailer at 7 pm Friday night. Yes, this looks a bit janky, but there was no time to make flares. We really just wanted to test this big wheel/tire combo on track to see if there was a prayer of TT2 competitiveness for later in the 2016 season.


I'm going to try to do this event coverage quickly, as it was only a 1 day event and we were just there to test the Corvette and BMW. I didn't really care how we finished, as this was really just an HPDE day that they were calling a "Club Trial" competition event. They had transponders but there weren't any classes, so they used a PAX factor to post "competition" times. Yes, an autocross PAX applied to road course times. I can't make this stuff up.

Anyway, we got there at 6 am, an hour before sunrise, and were working in the dark to have both cars ready before a 7 am driver's meeting. The C4 was unloaded, Amy and I did the wheel swap on her BMW, the AIM Solo lap timers were mounted, and we checked everything else we could under pitch black skies. The driver's meeting took a bit and after we got out, right as the sun was coming up, we greeted Brad and Olof from Vorshlag who had come to help. This became an eventful day of "track side car mods" so their assistance was most welcome.

The SCCA Club Racers had 25 entries spread across 5 run groups and Club Trials had 30 entries jammed into 1 run group. This is a 1.7 mile course and 30 cars spread out across a VAST array of skill and prep levels makes for a crowded track, but again - this was just a test for both cars.

They gridded the C4 in P1 and stuck Amy about a 1/4 of the way down the order. We went out into the first session and it was COLD with 40 degree temps and 20 mph winds all day. I could hear all sorts of tire rub on the out lap so I got the heck out of the way and dove into the pits before I held anyone up. But more importantly, I was able to test out 3rd and 4th gear under load. NO MORE OPTISPARK ISSUE! Engine ran strong all the way to 6000, so that's already a win. But getting no laps meant I'd be stuck at the back of the pack, which sucked.

Amy drove the whole session in the BMW with the rear tires rubbing the rear fenders badly, sending up plumes of tire smoke. Did she stop? No, the ran the whole session. Oh well, if she ruins her tires its her own fault. The Bilstein PSS coilovers were sprung too softly and allowed a TON of body roll, so we'd be doing a big spring rate upgrade immediately after this event.

continued below
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25 Jan 2016 03:51 PM
continued from above

The fix for the rear tire rub on the C4 was to add more rear wheel spacer. We had all the spacers in the trailer stacked to make nearly a 1" spacer, which moved the rear wheels outboard enough to rub less on the inner fender sections. See why I wanted the long ARP wheel studs? Getting no lap time for the C4 put me at the back of the grid for session 2, right next to Mark Council's C5. His transponder didn't work so he got no times, either. So the two of us went from P1 and P2 on grid to P29 and P30.

Mark's C5's 4th gear synchro let go right in front of me at the beginning of Session 2 (its already getting a C6 Z06 trans installed at our shop), but I went around him and started picking off cars on every straight. The rear was very bouncy - stock shocks aren't made to deal with 345 Hoosier A6 tires! - but I could drive around it. We're going to need to massively increase rear spring rate and put some real shocks on this car if we keep the big tire setup.

So there were lots of spins and traffic in session 2, and I spent the entire time passing slower traffic, but I did manage to get a quick enough time (1:27.9) to move me to P8 on grid for session 3. The C4 also made 5 laps - in a row - which I haven't ever done in this car. This is already a successful test.

In session 3 the C4 was passing cars pretty quickly and I managed to lap some other folks 2-3 times in this session. The weather was holding so far (no rain yet) but it was still bitterly cold. Amy's 330 had gone through two different fender rolling jobs in the pits by now, which was a giant PITA.

Track side fender rolling sucks - this should always be done in the shop! - but parts delays & C4 prep ruined our schedule on the E46

I found a new issue at the end of session 3 - the brakes went away after 6 laps. There was NO pedal at all. WTF? I wasn't even pushing the brakes that hard, and we had added the brake cooling up front. Fresh XP20 Carbotech pads, new Centric 13" rotors and Motul 660 fluid should have lasted longer than that. The cornering speeds were way up on the big tires, so I was going down the straights faster, but nothing like we did in the TT3 Mustang (this C4 feels like it has less than 300 whp - come to find out later, it does). You can see this at the end of the 4 minute video, linked below.

After I lost the brakes I dove into the pits, limped it through paddock and barely got it stopped in front of our trailer after pumping the brakes many times. Brad and I bled the brakes, which already had Motul RBF660 and almost no laps on the fluid. A little air in the right rear but a LOT in the left front (that's a clue). The new front brake calipers had less than 10 total laps on them. The AP caliper temp indicator strips didn't show much heat in any of the calipers, but the left front was a tick higher at 370°F (the other 3 calipers barely registered on the strips). That temp shouldn't boil Motul 660? Maybe the fluid had been in there so long it had absorbed water? Oh well, it was fresh after a full system bleed.

With a quick time I was gridded P1 in session 4, but it started to rain before we went out. Oh great, giant slick tires and I don't even know if the wipers work! I was going to just make some laps in the wet and test the brakes again. I let the C5 Corvette gridded P2 go around me at the start, as the old Hoosiers take a lap or two to get up to temp, but I reeled that car in and we both caught the back of the field at the end of the first hot lap. Like I said, big discrepancies in lap times in this large 30 car field, spread out on the short 1.7 mi course.

After a number of passes I got little bursts of clear track, and the rain wasn't much more than a sprinkle. I was gaining confidence in this janky test setup more and more, taking corners faster, braking less and less for the high speed sweepers like Big Bend and Ricochet. I was almost feeling like I could take come of these fast corners with the throttle matted.... almost.

Again, after 7 laps of mostly traffic, the brakes went away abruptly. No hints, not softness creeping into the pedal, instantly gone. Just nothing there. At all. Luckily I was held up behind a BMW for most of a lap and had backed off to about 50%, trying to build a gap. When I sped up to take lap 8 at speed, going into Big Bend, I went to touch the brakes... FLOOR! Nothing. Well luckily there was some "grip reserve" and I was able to take Big Bend without any braking whatsoever, hehe.

I dove into Pit In, downshifted a few times to slow down, then crawled to the paddock in 1st gear. I pumped the brakes furiously, nothing. Had to shut off the motor with the car in gear in the pits to get the car to stop, or else run into the back of the trailer. Yikes. Glad I did that session to test the freshly bled brakes, since this is not the fluid boiling. Something else is going wrong. We let the car cool off, winched the Corvette into the trailer, swapped wheels for Amy's BMW so she could drive it home, and got out of there before the rain got any worse.

Raw time results from session 3 (dry) and session 4 (wet). DangerZone was quickest of the day?

The C4 was once again fastest in "moist" session 4, and only a 1/2 second off my dry session 3 times. Again, I was still learning the car and this new "big tire setup". The 1:23 lap times aren't all that impressive on their own, as we've run 1:17s in the TT3 Mustang here - but we did that in much warmer weather. This January weather was brutally cold and the other racers were commenting that their times were 2-3 seconds off the mark. Whatever, don't care much about lap times this day - this was still a productive test for both cars and we learned a lot.

I came away from this test feeling... cautiously optimistic? Some of the folks here would be at the NASA TT event the following weekend, so I could compare to them there. This was the first time to really put laps on the new springs and rebuilt shocks - the front felt pretty planted (1170 #/in custom transverse spring by VBP) but the rear didn't feel good at all (510 #/in stock '84 Corvette Z51 rear spring). There was a lot of rear suspension "wallowing" that had me a bit concerned. MSR-Cresson is notoriously VERY SMOOTH and the back still felt unsettled. How would this work at MSR-Houston, which is much bumpier in sections? Could the rebuilt but still stock dampers handle the added grip from the 345mm A6 tires? Are the 25 year old, rotted rubber suspension bushings going to bite us now with the bigger grip? We would see in a week...


We unloaded the C4 on Monday morning and took a closer look at the caliper temp strips and the tire rub evidence. Wow, the rears really self-clearanced the fender liners. The most damage was done on the very first lap in session 1, where the inside rear sidewall on the right rear dug into a suspension bracket (see below), which cut a groove into the edge of the tread. This initial rubbing was why we added more spacer and swapped the rear tires side to side. We kept an eye on this tire all day at MSR-Cresson - the groove never worsened - but this tire will still be thrown away and never used again.

The calipers barely even registered any heat at all, so the brake cooling wasn't the issue. Ryan and Brad tried to re-bleed the brakes but it never got better - car had "no pedal". This meant we had a bad master cylinder. I made some calls and the previous owner of this C4 (Matteucci) mentioned that he had replaced the master cylinder once already (installing a reman 96 model). We also noted that another C4 customer in the past had gone through 2 or 3 masters as well. Its back to "old car problems" again - a freshly rebuilt master cylinder for a 1996 model (which ensures we get one valved for the 13" front brakes) was ordered.

We also scheduled a dyno pull at True Street, to get the legal pair of SAE corrected dyno pulls for TT1/TT2 classing. I thought briefly about running TT3, where this car should really be classed (for it's P-to-W and lack of aero), but we wanted to hopefully stay in the same class for the entire year for this car, and I really wanted to add aero and more power now that the "big tire test" seemed to be successful. And why run TT3 again, when we had already run that class successfully for 3 years in the Mustang?

True Street squeezed us in Tuesday morning (1/19/16) so we loaded up the C4 (with non-functional brakes) Monday night and I took the car there first thing on the morning of the 19th. The C4 was strapped down with the correct sized tires (first dyno test on the 345 Hoosiers, which will sap a little more power than the 245s) and after the engine was warmed up Sean made two dyno pulls in 4th gear on their DynoJet in-ground chassis dyno. Temps were in the low 40°F range, so there were bigger than normal correction factors.

The best it made was 296 whp and 363 wtq, using the common STD corrections. That translated to 288 whp/354 wtq with the SAE correction factor that NASA wants to see. Hmm, we've got a long way to go to make 380 whp for TT2, but that is a battle for another day. The dyno curve was smooth and looked remarkably similar to the bone stock 284 whp dyno curve done in January of 2015, but there's a solid 20-25 wtq bump from the bottom to around 4000 rpm, then the new motor seems to choke out and make nearly the same peak power number as before (284 whp then vs 287 whp now, both SAE).

Of course there's a restriction somewhere - either the anemic 1992 LT1 camshaft, the stock throttle body, the smallish MAF sensor, the stock catalysts, or the stock exhaust manifolds are choking the life out of this engine, but 296 whp is pretty normal for a stock LT1 with a super light flywheel. Remember, this car's 7.25" multi-disc clutch/pp/flywheel is a solid 50 pounds lighter than stock, which all translates to more engine acceleration, which adds power on a dyno - even if its kind of fake.

ARH makes C4 headers in 1-3/4" and stepped 1-3/4" to 1-7/8" primary long tubes, with an X-merge, with and without cats

For TT1/2/3 we can do damn near anything we want to add more power - heads & cam, crazy exhaust mods, an LS1 swap, turbos, you name it - but we'll look at a long tube header & freer flowing exhaust upgrade first, then see where we are on the dyno. The ARH long tubes for the C4 (see above) should add 30 whp by themselves, if not more. We'll ditch the 25 year old catalysts and the choked up after-cat system, which should add another 10-15 whp. So look for power upgrades to be added and tested throughout the 2016 season, if things work out with DangerZone in TT2.

After the two quick dyno pulls I loaded the car back up and got it back to the Vorshlag shop. Ryan quickly installed a new 1996 master cylinder and - viola! - the brake pedal is back. He also checked the car stem to stern for a pre-track inspection - nut and bolting everything, fixing some fender structure that had worn through, etc. They did an oil and filter change, going from dyno based high zinc "break-in" oil for the new engine, to 15W50 Mobil1 synthetic for the next 2 race weekends.

The crew also fabricated the rear tow hook, shown above. This bolts to the rear aluminum crash beam, which is pretty beefy - we should lighten that the next time the rear bumper cover is off (bumper cover is a total MOFO to remove - takes 2-3 hours, with small hands). This rear hook has a 2" inner ring, which is the required size by NASA and SCCA. Just nice to know its back there, if I nose this thing into the weeds and need a tow. Hopefully it will never be used.

The past 25+ years haven't been kind to the front air dam plastics, which were falling off and damaged when we got the car. One piece was held on with about 6 pounds of Gorilla Glue! The low ride height and shorter 245/40/17 tires we ran last year made this worse. Now that the car is sitting up a bit higher on the taller 335/345 tires it was time to swap on the new GM plastic pieces. Ryan had to reconstruct much of the support structure on the left (and scrape off the Gorilla snot) but he got them all on and aligned correctly. These pieces help force air into the "bottom feeder" radiator air intake, plus keeps some air from going underneath the car (reducing lift).


I was going to wait and include the write-up for the upcoming NASA event at MSR-Houston in this update, but it is already running long, so we'll cut it off here. Here is the first third of the NASA Texas 2016 schedule:
  • January 17-18 – MSR-Houston, Clockwise
  • March 14-15 – MSR-Cresson (the 1.7 if we have less than 34 cars in TT, or the 3.1 if we have more)
  • April 25-26 – TWS

Obviously we're taking the C4 in TT2 (and the E46 in TTD) to this weekend's NASA event. The TT2 competition signed up already looks brutal - 10 registered in class, including several Z06 Corvettes, a Porsche GT3, a race prepped EVO, and more. So yea, DangerZone might not pose much danger to the class right now. We're under powered for TT2 by about 100 whp, the rear spring rates are all wrong, and the shocks are laughably inappropriate for these tires.

So this first NASA event at MSR-Houston will be a "let's just get points" opportunity and more shake-down runs for this new "big tire" setup. I'm not even going to burn the set of Sticker tires here, since we'll be pretty far off the TT2 pace. Amy has one other TTD competitor so I'll try to help her do her best, but that car is also under-prepped for the class at this point. First event of the year - we both need a lot of luck to score points here, which might help us later in the season.

Until next time,
Terry Fair - www.vorshlag.com
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05 Apr 2016 04:48 PM
Project Update for March 25, 2016: When we last left off the C4 had been raced once at MSR-Cresson and set FTD for the SCCA Club Trials. There were some issues with the brakes, and the shocks didn't deal with the minor bumps at Cresson, both of which gave me pause... but I ignored that and pushed forward on the "Big Tire" TT2 plan. We did some quick fixes to the brakes, then went to with NASA at MSR-Houston, one week later. After that we had a little time, so we made some changes and ran another event with NASA in March, back at MSR-Cresson again. We played a bit of "musical chairs" this time, but I will explain the what, why and how below.


My last forum build thread post ran long and I left a few things out due to space. While I was writing the last few bits of that post, a few extra changes were being added before the January MSR-H NASA event, which I will go back and show below.

For the first "Big Tire" test at MSR-Cresson we had stacked up a bunch of smaller spacers on the rear wheels. We had spec'd these custom 18x12" wheels to actually fit the front with a 335mm tire, hoping that in the near future we would buy some wider 3-piece rear wheels (18x13"?) for the massive 13.8" wide 345/35/18 Hoosiers. If that happened then all four 18x12's we built the same way could become front wheels, leaving us with two full sets of race wheels again. Its always smart to have a full back up set of matching race wheels, so you can practice on your "old scrubs" and save the sticker set of tires for that "golden session" of the weekend.

To make these "fronts" fit out back for now we just used a couple of small spacers. During this January SCCA Club Trials event they rubbed inboard with the 345s, especially in hard corners, so we kept stacking more spacers out back until the rubbing stopped. The result was we were left with a LOT of tire poke at the rear (which I detest), but we were going to cover all this with custom built flares later, so I wasn't too worried. As long as the car still fit inside the trailer (it did, easily) it wasn't too wide. More track width adds mechanical grip, and since this wasn't an autocross car, the added width wasn't going to "kill the slaloms".

After this event, back at our shop I removed a rear wheel and measured "the stack" of spacers. I took this measurement and found 1-piece hub-centric spacer for use at the next event. This would be safer and less janky than a bunch of mis-matched spacers stacked up. I found .875" thick aluminum spacers from Bear Racing - the pair is shown above on the scale. These 1-piece spacers fit the hub bore and bolt circle of the C4 perfectly. I'll talk about how these were re-purposed later in this thread...

I forgot to show in my last post where Jon was adding new graphics for the move to TT2, as well as a few other new decals for Forgestar and the "Rampage" rear license plate. These are made on our 24" wide vinyl plotter, shown at right. Nothing fancy but it works well enough for simple graphics for our shop cars and a few customer cars we maintain at the shop.

Another thing that I had always meant to do to this car, even when it was in TTC (we had taken points for it), was open up the factory LT1 "air box". As you can see above, the intake manifold is fed by a rubber tube (now with a MAF sensor added) from an air filter "enclosure", or air box as we like to call it. By the way, there is no direct path for air to get into this semi-sealed area ahead of the radiator inlet duct. Air just bleeds around and through gaps in the bodywork to feed this area. We can (and eventually will) add a "ram air" inlet on the front of the car (front license plate pocket lines right up) to feed the air box with a good high pressure source of fresh air. For now I just wanted to open up the factory air inlet hole and remove the air baffle on the front of the air box.

Above at left is the unmodified factory airbox, which holds a pleated paper air filter and has a baffle on front - to cut down on noise and to keep the filter from getting wet. The "quietness" of this car doesn't matter to us now, nor does a little moisture from running in the wet (we don't even have real "wet" race tires, so if rain is falling this car isn't likely running). Getting more air into this choked up airbox was the goal. In stock form all of the air flows in through a single rectangular hole, after it travels through a plastic air baffle - which is shown above at right, already removed.

The real fabricators in our shop were busy on billable customer work so I hacked up the airbox myself, after we were closed one day. First thing I did was drill out the rivet heads to remove the air baffle. Then I scribed out two new rectangular openings on each side of the factory hole. This was done quick and dirty, with just a few measurements and a straight edge. I marked, center punched, then drilled some holes in each corner to make the new openings have rounded corners, to try to match the OEM hole. Then I used a small jig saw to join the drilled holes. End result was two new rectangular openings with rounded corners.

For being 25 years old the air box was in great shape. After the 2 new openings were cut, and the edges deburred and sanded smooth, it was ready to prep for paint. I scuffed the painted metal with some Scotch Brite pads and cleaned everything with wax and grease remover. Once that dried it was hit with 3 light coats of black paint.

This is the final result, above. I may have rushed the drying of the cleaning solvent, as the paint fish-eyed in some sports. Oh well, its hard to even see this air box with the clam shell hood up. More importantly - the baffle was gone and the surface area of the opening in the airbox more than tripled.

We looked at some aftermarket "cold air" kits for the LT1 C4 and the few choices still available were not very appealing. Sure, we should add a more direct path of fresh air from the front bumper to this now opened up enclosure, but for now it was a $3 upgrade (cost of paint) that was well worth the hour it took me to do. There is indeed more intake noise, so maybe there would be a tick more power on hand for the MSR-Houston event? I'd be running nearly 100 whp down on what a real TT2 car at this weight should be, so anything would help.

One last little update. After the January SCCA Club Trials, when the brakes failed in two sessions, we replaced the brake master cylinder with another reman unit (we cannot find new master cylinders for this car). This might be the 3rd or 4th reman'd MC this car has seen, but when it was installed and bled the pedal pressure felt right once again. Let's see how long this one lasts? As with all track cars we build, the cap to the plastic fluid reservoir got wrapped with a shop towel and zip tie, which usually soaks up the small amount of fluid that might puke past the cap under high temps. The original vacuum assist brake booster is still on the car - and its a PLASTIC unit that is a known failure point. More on that in a bit.


The MSR-Houston track is not nearly as smooth as MSR-C, but that thought never entered my mind before we got here. Why? I've always raced cars here with GOOD monotube adjustable coilovers, so it never felt bumpy in the 7-8 times I'd raced here before. Boy was I in for a surprise in #DangerZone!

We took both the Corvette and BMW to this 2016 NASA season opener event at MSR-Houston. We loaded up Friday morning and slogged through 6.5 hours of driving, most of which was burned inside the city limits of Houston dealing with their nightmarish traffic (normally this is a 4 hour drive from Dallas). I was towing our enclosed trailer with the Corvette inside and Amy drove the TTD classed BMW 330 down.

When we arrived it was pitch dark and the paddock was packed. We got lucky and found a wedge shaped spot close to grid where we unhooked the trailer and parked the BMW. Amy had Tech inspect the BMW for Annual TT Tech and a new Logbook.

It was too dark and too late to extract the Corvette and make the close of tech that night, so we got to the track early Saturday morning to take it through annual tech before the first TT session. Well, in the rush we did not put the safety wire into the Schroth harness clips in the C4. Without it, we could not pass tech. I pulled out of line, went back to paddock and added the safety wire to "lock" the clip-in latches closed. I got back in line to re-tech but the TT field had already gone out on track. I got my tech sticker, drove straight to grid, belted up and went out on track.

They threw the checker as I came around on my warm up lap so I didn't get a time. This meant I'd be starting from the back of the grid, which makes for an extra challenge. I was also trying to drive BOTH of our TT cars both days, so I had my hands full.

This was the debut NASA event for our BMW E46, which we had planned on running in TTD for 2016. We're doing a "build progression", with parts being added along a set build plan, hopefully showing incremental improvements along the way and testing products we make or want to offer. So at this event the BMW was PAINFULLY under prepped (150 pounds over weight + 50 whp down). Unfortunately, the Corvette was also very under-prepped for TT2.

We had a little bit of a break after the first "warm-up" TT session, which is only used to get times for the gridding of cars in the first "official" TT session. So I had no time in the TT2 Corvette and gridded at the back in this next session. I went out on track hoping to get the tires up to temp by lap 2 or 3. That ended up never being an issue - even when "cold" these massive A6 Hoosiers make MONSTER GRIP. Lots of people think that if a tire isn't at its peak temperature that it will have zero grip. That was NOT THE CASE in this car... it made TOO MUCH grip from the very start.

Event Photo Gallery: https://vorshlag.smugmug.com/Racing-Events/NASA-MSRH-012316/

The massive mechanical grip plus the bumpiness of this course added up to one of the scariest laps Ive driven in my 29 years of experience with track events. There is a straight section of this course between T14 and T13, right before the hill you almost jump they call "the launch", which was especially bumpy. I had to back off a lot here just to stay on the track. I have never noticed the bumpiness there in any previous car I've driven at this course, or in our BMW this same day, all of which had been on proper shocks. Driving this track in the C4 was a "life altering experience". After a couple of laps and almost skidding off the track going in a straight line I pulled into the grid, white as a ghost.

That. Was. Not. Fun.

I realized, right then and there, that this Big Tire test was a terrible idea without buying real dampers and changing some other components. Adding 100mm of tire, and going from an R7 to an A6 compound, showed the true limits of the 25 year old Delco Bilsteins. I had run this track the year before in this same car on the little 245s to the tune of 1:43.7 without any handling drama... this day on 335/345mm tires I could barely manage a 1:48.9 with a fresh motor and many other upgrades.

continued below
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05 Apr 2016 04:49 PM
Continued from above

Five seconds slower, just from lack of control. It wasn't "more rolling resistance" or "not enough heat in the tires", no the cause was "bouncing off the bump stops" with an uncontrolled suspension setup. The GRIP was definitely there, but I simply couldn't use it when the track got bumpy.

I parked the C4 and ran the two remaining TT sessions in the BMW, where we had a shot at winning TTD class. And we did win on Saturday, but it was close. The C4 was WAY back in the TT2 standings from this lone session with 2 hot laps.

Good party Saturday night, but it was cold all day and into that night. It was 32°F in the morning, got up to the low 40°F temps during the afternoon, but the wind never let up and we were always cold Saturday. The track did warm up enough to put some quicker TT times down at the end of the day.

It was foggy, humid and damp for the first TT session but I wanted to get another lap in the C4 out of the way, so I ran that car first. I finally put the vidcam in, dried off the dew inside the windshield and back glass (we really need a defroster in this car), and lined up in 18th out of 38 on the grid for TT Session 1.

Click here for in-car video of the bumpiest, scariest lap around MSR-H

After getting out of traffic on the first lap I made one hot lap and ran a 1:46.991, quicker than I drove Saturday, but still 3 seconds off my 2015 TTC lap record on the little tires. The lap was still very sketchy, bouncing around like crazy. You can hear me comment on the video with things like "Wow, that was scary" after Turn 13. The rear suspension was hitting down on the bump stops and going up to full droop... it was much worse inside the car than the video shows.

With the same minimal safety requirements as HPDE, there are stark differences in safety gear used in TT cars

As I came around the last turn on the lap shown above there was a C5 parked in the middle of the track, right under the Start/Finish stand. It had just backed into the pit wall hard and was totaled. The driver is lucky to be uninjured - he was using nothing more than a helmet, stock seats and stock 3-point belts. I had to back off and pull off line to miss the car (it happened only seconds before I got there, and there was not a yellow at the previous corner station yet). Made me appreciate our decision to fully cage the C4 and invest in a HANS and other safety gear. And made me rethink letting Amy out in her TTD BMW with none of these things, too.

I am posting pics of the crashed TT car to share what can happen to people at any track event, if things go very wrong. I hope that maybe some folks will have that "light bulb" moment after seeing this and upgrade their personal safety gear. /off soap box

Once again, after the first TT session in the Corvette that day, I came in and parked it. Nothing had improved magically overnight and it was still way under damped for these tires, springs and track surface. Everything was moving around, uncontrolled, and I recommend you NEVER do this. The sad thing is that I knew better, damn it. I might should have gone with smaller 315s and of course spent the money on REAL shocks before trying this test. I just got greedy!

With fielding 2 track cars this year, a business to run, and coming out of our slowest time of the year I just couldn't afford the $4500+ in dampers and springs and bushings that these tires demanded. It was a gamble but it didn't pay off. Running these big, sticky tires on 25 year old shocks was flat out dangerous. #DangerZone was supposed to be a joke, not a real motto!

Parking the C4 for the day freed me up to be able to ride right seat with Amy (above left) in an HPDE3/4 session, to try to instruct a bit and get her confidence up. In just a few laps she had found 2.5 seconds (it was all in the braking zones) and was back in the TT fight. It felt good seeing that big of a time change just by giving her a few pointers. I might actually try to Instruct with NASA again... I kind of miss it.

I ran the BMW in 2 more TT sessions (2 and 3) mired in traffic, but I had what I thought was a healthy lead in TTD towards the end of Sunday so I let Amy drive the E46 in the 4th TT session... and sure enough, her BRZ competitor in TTD found a bunch of time and got the win on day 2. Oh well, we still have a LOT of work to do on this Bimmer.

Left: On Saturday the C4 was 6th in TT2, 330 was 1st in TTD. Right: On Sunday the C4 was again 6th in TT2, 330 was 2nd in TTD

This race weekend was a mixed success. The up-classed TT2 Corvette was way off the pace for both the class and the times I had driven here last year in TTC. That car took 6th out of 10 in TT2 on day 1 and the had same finish position on day 2. While the suspension setup was a bust, at least it ran reliably, was leak free, and the rebuilt engine never skipped a beat or blew any smoke. The BMW 330 was also a bit off the pace of the old TTD track record (1:48.4), but it did OK for such limited prep in its debut event, with one 1st and one 2nd place finish for the weekend.

Hey.... we don't need TWO Archer themed Corvettes, hah

We learned plenty at this event and still had a LOT of fun - seeing friends, the Saturday night NASA party, and both of us getting plenty of seat time in the BMW. The dismal results in the C4 made me rethink this new direction for Project #DangerZone.


After the shellacking I took at MSR-Houston, we had nearly 2 months to think about the C4 would need to do to make it a more competitive (and safe) TT2 entry. I started adding up the cost of parts and the work it would need:
  • $4500-5500 in MCS doubles, springs, and Vorshlag spherical top mounts
  • New Delrin/Poly/spherical bushings at every suspension pivot location
  • A new set of heads, camshaft and valvetrain upgrade, maybe a new intake manifold (to his 380 whp)
  • Full length headers, custom exhaust, and a better tune (to his 380 whp)
  • Custom flares at all 4 corners
  • Splitter, big wing, ducted hood for some downforce
  • Thermostatically controlled oil cooler, Accusump, and other oiling system upgrades
  • Aftermarket carbon fiber hood ($3000) to lose more weight

The list kept going beyond this, which was long after my budget gave up. These numbers just didn't make sense a car we really don't make any parts for, that is based on 33 year old chassis, and with a motor I had just spent several thousand dollars to have rebuilt to painfully stock specs. What was the purpose of this TT2 class move? Just to have "faster lap times", but yet give class competitiveness or require a LOT more money to handle as well on the big tires? Deep thoughts.

We kicked around some ideas internally and on Corner-Carvers about an LS swap, but the hours and cost projections kept spiraling out of control. This C4 was supposed to just be our "tweener" build, done on a tight budget, to bridge the gap between our TT3 Mustang and the Next Big Shop Build. Now we were talking about a $40K+ showcase car... that was based on a vintage chassis? This didn't really reflect what we do at our shop, and was the epitome of bad judgement, so I went through the Pros and Cons for a week or two.

Meanwhile I asked our crew to look into a couple of small fluid leaks that I only noticed in the trailer coming back from the MSR-H event. First fix was building a power steering catch can, shown above. The pump was spewing a small amount around the cap.

We had this non-vented oil catch can lying around from another project, so that was re-purposed to catch the puke from the power steering pump that was getting past the (new) fluid reservoir cap. The next was an oil pan drain plug leak that has been weeping just a little fluid. I abhor fluid leaks, and the new copper gasket fixed that, mostly.

As I was staring at these big, meaty tires one day, Ryan pointed out that the rear tires had slipped on the wheels. He had marked the location of the tire valves when he installed these 345mm A6s and they had slipped a good bit (the fronts had not). Must have been from that massive 354 ft-lbs of torque, LOL! Not uncommon on freshly powder coated wheels, so we will scuff up the inner lips once these tires are off, which should give enough bite to keep the tires from slipping.

By this point I was thinking of ways to get the car back into TTC, but how do we cover up that MESS that I made of the fenders?? We cut all 4 fender lips off to clear the big tires, and the car would look turrible with the 245s back on.

Around that time an old college buddy, Jason, brought his BSP autocross prepped 1989 Corvette by the shop, above. He took off the 17x12" autox wheels and mounted up some 18x10.5" Z06 street wheels at all 4 corners and got the dang thing registered and inspected. It being over 25 years old made for a simple $7 inspection of lights, wipers and horn. And the Vintage plates were like $70 for 5 years! But more importantly, I looked closely at his rear flares. These were just the GM "export" flares for the C4, also used on the 1996 Grand Sport to cover a slight poke from a 17x11/315mm factory rear tire they used. Hmm.

Jason and I had discussed the C4 many times over lunch in the following weeks, and I was bouncing ideas off of him about the "Big Tire" test, how badly it went and how expensive it would be to keep going down this path. He, like many others, told me what I didn't want to hear... you gotta give up the big tire and put the car back in the class it was built for: TTC. I had also acquired another chassis to build for a shop car that could actually bring us some actual business, so investing a lot more in the C4 was not wise.

345 vs 245 Hoosiers - just look at how much rubber I'm having to give up!

One argument made was that a fully prepped TTC Corvette would sell for more than a half-assed prepped TT2 C4. This was a difficult choice, but it made the most sense for the business. Painting the car and cage would help resale value, and that was something I needed to plan for.

Yeah, it was time to go back to TTC for Project #DangerZone.

I decided to buy a pair of the Grand Sport flares, just to see if they covered up the sins we created when we cut the rear fenders to clear the 345mm tires. Sure enough, the rear fender cuts are almost 100% hidden under these... so we conceivably have an easy way "back to TTC", if needed.

With the sticker set of 245s already mounted on the 2nd set of SSR 17x9.5" wheels it was a quick change to go from 335F/345R A6 tires to the 245 R7s. I re-ran the numbers, weights and power for the 2016 rules and realized that since the car had to weigh 3260 pounds for this year, now we could make up to 291 whp. And since the rebuilt 1992 LT1 made 288 whp (SAE corrected), I wouldn't have to run even more ballast to make up for the 4 extra whp it makes now (it made 284 whp before the rebuild). So for 2016 we would need to just run the 58 pounds of extra "minimum weight" ballast.

One small last thing I decided to modify for TTC use now was to locate a second pair of the Bear Racing .875" thick spacers for the front, keep the rear spacers in place, and widen the track with the skinny tires. We can increase track width up to 4" over stock in TT-Letter classes without a penalty, and this spacer addition would add 1.75" of track at both ends. More mechanical grip is the payoff, and if you can keep the tires out of the side air stream it doesn't add any aero drag.

This is what we ended up with, above. It has some monster fender gaps but the car is actually sitting very low (maybe too low - we are addressing this soon). At this point I had pulled the "TT2" class designation decals off and Jon was cutting some "C" decals for all 4 corners. I signed up both cars for NASA @ MSR-Cresson - TTD in the BMW and TTC in the C4 - including one Instructor entry for me. Amy was supposed to run the BMW, but had a death in her extended family which required her to travel across country over the race weekend, so at the last minute I was looking for a way to get both cars to the event...


It rained the entire week before this event but it looked like it would clear up sometime Saturday. I mentioned to my crew here that I needed someone to fill in for Amy. Our Order Desk Manager Jon started talking a bit of smack, so I surprised him with an offer to drive the red BMW in HPDE, and he took it. We did some last minute prep on that car and he drove it out to Motorsport Ranch Cresson on Saturday morning. I left the shop at 7:20 pm on Friday night with the C4 in the trailer and slogged through the rain to get to the track. I was unhooking at 9 pm, in the pitch dark, parked in the grass, on a steep hill. There was NOWHERE to park, as even with the rain looming, over 200 people showed up to run HPDE, TT, and W2W.

continued below
Veteran Member
Veteran Member

05 Apr 2016 04:49 PM
continued from above

Saturday morning it was still wet and sprinkling, so I drove the BMW in the TT Warm Up on street tires, with Jon riding shotgun. I had hoped to show him "the line" (this was his first time driving at MSR-C), but anywhere on the 16+ year old, original track surface that was "the line" was polished smooth. Add in the water and it was like driving on ice, so the trick in the rain here is to NOT drive anywhere near the proper driving line. The marbles is where the grip is, strangely enough.

Event Photo Gallery: https://vorshlag.smugmug.com/Racing-Events/NASA-MSR-C-031216/

After that drift-fest TT warm-up we came in - and realized we forgot to install the AMB transponder on this car. No official time, doh! So that meant that I would be gridding in the next TT session at the back, no matter which car I brought to grid. I ran the red 330 again and got a time good enough for the win for the day, but I was itching to get into the once again TTC classed C4. This would be the first time it has been run in TTC with the fresh motor, on a sticker set of tires, with the upgraded spring rates, and the "rebuilt" OEM shocks. Aka: the most prepped it has ever been for any class.

After lunch the rain finally let up and began to dry, so we unloaded the Corvette. The track surface dried off in TT session 3 and I took the C4 out for the first time on Saturday. We had 6 cars in TTC class so whoever won today could potentially take home 2 Hoosier tires. I was mired in traffic and couldn't get a clear lap, ran a 1:24.X in the session with 2-3 passes per lap, but I at least moved up the grid. The old MSR-C 1.7 CCW track record for TTC was a 1:25.1, and both BJ and I had both beaten that already.

In the final TT session of the day I was trailing BJ Meyer badly in his TTC prepped Mini Cooper S (parked to the left of me in the image above). Supercharged, on coilovers, lots of boost, and driven well at this, his home track. In the final TT session of Saturday I put down a blistering 1:22.206, with only one semi-clear lap for traffic, with a number of small driving mistakes. But BJ put in his personal best of a 1:21.996, taking the win for the day. My time was good enough for 2nd, but I knew I had more in the car - predictive showed some high 1:21's but traffic kept killing my best laps. At least I'd be further up the grid for Day 2!

Jon was in HPDE3/4 and as the track dried up we swapped on the Hoosiers and he was having a blast. I saw the TT "needle go into the vein" for Jon this weekend... he's been cooking up TT builds on paper all week!

Sunday morning was a bit of a mess, and it was my fault. This was the Daylight Savings "leap forward" day, where we lose an hour at 3 am. My smart phone alarm can catch that, of course, but the problem was I set the alarm for... a weekday. So I overslept and made us super late to the track. We rushed to the track from the hotel but I made it in time to get into the 330, throw some fuel in it, and make it to grid with 1 minute to spare. I ran the first TT session in the BMW and again was mired in traffic. Getting a good lap in a gutless car that cannot pass anything is actually pretty difficult. I ran a 1:27.604 in the car Saturday but only managed a 1:27.854 on Sunday in this, the only session I ran the 330. Turned that car over to Jon for the rest of the day and spent the the other trying sessions to chase down that damned Mini in TTC!

In TT session 2 the Corvette was at least gridded 11th out of 39, so there should be a better chance of getting a traffic free lap? Well, not so much. I was on a quick lap and lost track of which car I was in... there's three left handers (T5 - T6 - T7) in the back section of the 1.7 course that I can take with the throttle matted in the TTD BMW, but not in the C4. Well I mis-remembered that, and kept the gas pedal mashed, and put two wheels off at the exit of T7 (Tombstone). And the grass was still wet, so that two off quickly became 4, which turned into a big graceful loop across track and into the grass. Yea, I spun it, which DSQ'd the session. I came back in and tried to get my head on straight.

BJ was checking to see if I was going out in TT session 3, and I told him that I damn sure was. So I got to grid for that session and all 3 of the top TTC cars were lined up pretty closely. BJ's Mini was sitting on a 1:21.8, I was gridded right behind him, with Mark Schnoeer's TTC M3 just behind us both with a 1:24.8 (last year's record setter). I needed to get the lead out and put a clean lap in for the day in the C4. I knew the C4 had enough performance in it to beat the Mini - it had beaten it every time before - but there was the whole driver thing I had to do.

I didn't know how much more the master cylinder had in it, but I was going to push for the win in this session. The first two laps of this session were traffic, and I passed some of the faster cars gridded ahead of me, but BJ was always right there about 30 yards ahead, too. By the start of the fourth hot lap I had passed the cars ahead I needed to, built a gap to BJ's Mini so I wouldn't be running into his mirrors, and got the 245 R7s up to temp. The brakes felt OK so I went for and achieved my best lap of the weekend....

Sunday TT Session 3 in-car video

All weekend I'd been touching 106 mph entering Big Bend and on the next straight reaching 110 before braking into T9. With these short tires, 110 mph is at the top of the rev range for this LT1 engine, so I started using 5th gear right before the start finish, and it gained me 2-3 mph (noted 112-113 mph into T9 on those laps). If you listen carefully in lap 3 in the video above, as I'm exiting the fastest corner of the course (Big Bend) I am running out of revs in 4th gear, so once again I planned to use 5th. I looked and saw that Predictive Timing showed me 1:21.6 right as I go to grab 5th... and CRASH! Synchros balk not once, but TWICE! It finally went into gear as I'm cursing the Germans who built this gear box. Even missing 5th gear twice the AiM logged a 1:21.90 lap time.

Son of a... Hindsight being what it is, I should have left it in 4th, because the 5th gear synchro has been "hit or miss" since we bought this car. Its an EXPENSIVE rebuild on this ZF 6-speed, too. Would it have been enough to get ahead of BJ's 1:21.618 he ran in that session? Who knows. At least I knew I had dipped into the 1:21s, which was a goal all weekend.

To make matters worse, after lap 4 in that stint I lost the brakes almost completely, with a VERY long pedal braking into T9. No brakes and no way to fix it at the track, so I missed the 4th session. Oh well, that 1:21.9 would still feel good for 2nd.

No, it just keeps getting better! The AMB timing loop borked that lap and showed it as a 1:03.786... Of course they had to throw out that bogus time (which was during my best lap of the weekend) and used my next quickest of 1:22.786 from that session (in traffic). Sure, its nearly a second slower than what I really ran, but I get it - timing equipment isn't infallible.

Even with a solid margin for Sunday, and after I told him I was done for the day, BJ still went out again in TT session 4 and dropped to a 1:21.589, resetting the TTC record with a strong number. So once again I was 2nd place in the C4 for the day.

During the weekend I was instructing with 4 different HPDE1 students, and sometimes sprinting to the grid to meet them in time for their sessions after getting out of the two TT cars. The grid was way back on the 1.3 mile course, due to the lack of paved parking area on this wet event site. Instructing was fun but made for a hectic weekend and a lot of running around - I need to get a scooter or small track support vehicle, something to get around the paddock in.

So once again the weekend was a mixed success. Driving two TT cars + instructing + talking to customers at our ever-busy trailer makes for a hectic weekend, but it was also a lot of fun. Jon got a check ride for TT and should have his comp license the next time he shows up to a NASA event. I managed two 1st place finishes in TTD (with only one timed TT session each day in this very under-prepped car) and two 2nd places in TTC. At least we were closer to the class winner in the C4 in this class, and we smashed the old TTC track record by nearly 3 seconds (but BJ reset it 3.5 seconds quicker than last year).

We run the same 245/40/17 Hoosier R7 on both cars, so the C4's old tires become the BMW's new rubber, heh. After switching the tires on the BMW back to the streets we moved the trailer to pavement and loaded the Corvette for the trip home. If there was any brake pedal I'd have run the last session to try to chase BJ Meyer down. After instructing in the 5:20 pm HPDE session, I didn't get out of there until after 6 pm, and that 2 hour tow home made for a another 12 hour day. But compared to my normal 7 day a week work days, this was a breeze!


After seeing results that were quicker on the 245 R7s vs the 345 A6 tires, it looks like we're heading back to TTC for the rest of this season. Jumping 3 classes up with just a tire change was foolish, and the proper path involves spending a lot more money than we have budgeted for this car.

At a smooth track like Cresson I ran a 1:23.7 in January at the SCCA Club Trials on the Big Tires (335F/345R), yet I ran nearly 2 seconds quicker (1:21.90) on the little tires with no other changes in March. Being the "fastest car of the day" in January gave me a false sense of confidence, and over-shadowed how the car felt in bumpy sections of this course. At MSR-H the car was tougher to drive on the Big Tire setup, just due to the rougher track surface. In TT2 there I was 3 seconds slower than my 2015 pace on the narrower TTC tires.

Please don't confuse this handful of "data points" with busted theories that "narrower tires work better" on a road course for any given car. I made some posts on Facebook (#SmallTiresMatter) that were in jest, but several people took them seriously. We've proven the small tire theories wrong, time and time and time again. A lot of folks have a lot of theories on why we were quicker on the narrower tires, but trust me... its just a simple matter of the current shocks not working well with the MUCH higher grip levels the wider tires made.

With the right shock and spring package it would be quicker on the Big Tires. Always. We made big drops in lap times on our TT3 Mustang on each jump up in tire size, going to the same tracks. We went from 265 to 305 tires, 305 to 315, and 315 to 335/345, and each increase in width was a drop of 2-3 seconds per lap. Big Tires Do More Work. You just have to upgrade the rest of the suspension to deal with the higher mechanical grip levels. 25 year old OEM dampers ain't the hot ticket on 345 HoHos!

If we had the points for TTC, I'd still install some adjustable MCS dampers for this car. There are still handling issues on even the smaller tire with the factory shocks, just not as pronounced. We're just "point maxed" for TTC right now and cannot add any more mods. Raising the ride height will reduce the chances of hitting the bump stops on bumpy courses, which it still does on the 245s, so that is planned before the TWS event. Here's our TTC build point budget:

Base classing: TTC*, 3260 pounds
- 7 penalty points for the base class "star"
- 10 points for the Hoosier R7 compound
+ 1 bonus point for running 10mm smaller than TTC base tire of 255mm
- 1 point for cold air mods / vented hood
- 3 points for spring rate change
= 19 points allowed within the first class (1 more point moves it to TTB)

Shocks would be 3 more points we don't have. The inherent TTC class competitiveness on the smaller tire, and budget constraints, just doesn't make sense for us to upgrade the suspension and other parts to make the big tires work on THIS car.

For TTC use this season we do have some small changes planned to make the car easier to drive and maybe a tick more competitive. A change to a smaller diameter racing steering wheel and a quick release will make it easier to see gauges + easier to get into the cabin of this car (after removing the steering wheel and hanging it out of the way).

A full Tilton brake and clutch pedal assembly and firewall mounted Master Cylinders will be going in soon. Those will replace the factory pedals and OEM master cylinder (for zero class points), so we can hopefully get past these crappy reman MC units failing so often. Removal of the OEM plastic brake booster is another failure point we can lose, also.

Next few NASA Texas events:
  • April 22-24 – Texas World Speedway
  • May 21-22 NOLA Motorsports Park – Crossover with NOLA
  • June 11-12 – Hallett Motor Racing Circuit
After that we will add the small over-flares to fix the cut off fender lips, then maybe... hopefully this summer, get some new paint on the body and cage/interior. Check back next time to see what we do next to #Dangerzone to hopefully make it less dangerous!

Terry Fair - www.vorshlag.com
Veteran Member
Veteran Member

09 Nov 2016 06:54 PM
Project Update for November 9th, 2016: On this, the day after an historic election, I think we need a distraction. Let's talk about race cars - welcome to the #DangerZone!

A lot has happened to our C4 Corvette since my last post. We developed a custom dual Tilton master cylinder brake setup to replace the constantly failing stock masters and booster. Then we tested that at an HPDE event and it worked flawlessly. Then we prepped the car for paint and off it went to my buddy Shiloh's shop. Afterwards the car came back SO beautiful we felt obligated to spruce up a few other things. Long story short - its now too pretty for me to own and race anymore, so the car is For Sale. Read below to catch up!


After four rebuilt OEM brake master cylinders failed on this car we were out of patience with the stock parts. These were not lasting a weekend and the failure mode was pretty abrupt: one lap you solid had brakes, then on some random corner the pedal would go to the floor and you had nothing. Bleeding wouldn't help a bit. Luckily none of these failures led to a crash - so far.

Jason had been wanting to make a brake solution to fix a situation just like this for years. This would replace the stock bake master cylinder and brake booster. As I have mentioned in the past the stock booster is PLASTIC on the C4 and they fail regularly as well (this car already had one rebuilt unit installed).

Real race cars tend to not use vacuum assist brakes or OEM stepped bore master cylinders. For safety and tune-ability they use two separate master cylinders, which can vary in bore size, and tend to use them with new pedal(s), either hung from above or from below.

Racing dual aftermarket master cylinder setups are almost always setup with one master cylinder for the front and one for the rear, plumbed independently for safety. A "balance bar" can then be employed to adjust the brake balance from front to rear quickly - literally by pressing on one master cylinder more than the other, via a lever at the brake actuator rod.

Race cars with manual transmissions (which is most) will often also replace the clutch pedal and master cylinder at the same time, so there are 2 pedal/3 master mounting kits you can buy. And if the brake and clutch master cylinders are hard to access (on the floor or under the dash) for fluid checks/refills, the fluid reservoirs are often remote mounted elsewhere, like above.

The trick in mounting these into an OEM chassis is having something to mount them to - usually top hung pedals are mounted to a roll cage tube, and bottom hung are mounted off the floor. Those both take lots of time to mount and brace. Sometimes you can mount the brake masters and new pedals right to the firewall, but usually they still need some support from a roll cage. We have done dual masters all 3 ways.

There are complete "pedal box" kits you can order, sometimes even for a specific car. Most race cars with gutted interiors and roll cages are built using generic pedal kits, like the Tilton above. Mounting top mounted or "hung" pedals from a roll cage tube is a good bit of work, and there is still a lot of factory wiring behind the dash panel on this car (it has all of the working gauges). Floor mounted pedal boxes are slightly more common.

These are the parts we sourced - the Tilton MCs, Tilton balance bar, Tilton remote knob, and the pedal multiplier

The main issue we had was that the factory floor on the C4 is too narrow and is somewhat weak (fiberglass) and the firewall isn't really open to adding in more mounting holes (fiberglass), but the OEM brake booster opening is fairly strong - see below at left.

We also didn't want to replace the stock pedals because, well, that's a bunch of work that is very difficult to un-do. We wanted to test a theory so a bolt-on solution that uses factory mounting holes was preferred - if this didn't work we could just put another new brake master and booster back on.

The solution (above) we came up with is a setup that has a CNC billet aluminum bracket / mount that bolts to the OEM booster mounting holes at the firewall. This way we could keep the OEM brake pedal arm and bracket. No cutting, no fabrication to the car at all, purely a bolt-on assembly. This firewall bracket has a pedal multiplier setup built inside that changes the pedal effort for the now manual brakes. This make the brakes have more of an OEM-like amount of brake pedal travel. We might never make another one for a C4, but this would be a good test for an idea for other, more relevant cars that might need this solution.

Forward of this billet firewall bracket are four studs that hold a steel bracket, to which the two Tilton master cylinders are mounted. In between the pedal multiplier and the masters goes the actuator rod and balance bar. This leads to a dial on the dash to adjust front to rear bias on the fly.

It took some tricky machining on our CNC mill to make the main billet aluminum part, but we wanted some new challenges for our machines. Jason made this piece in 3 CNC setups and mounted the pedal multiplier to the main pivot.

Ryan built the steel bracket that the two Tilton master cylinders mount to from a CAD drawing. Then all of this was bolted together into this assembly shown below. He then made a custom actuator rod that connected to the factory brake pedal under the dash. The rest of the pedal assembly was left stock. This was done to make this a bolt-in upgrade.

Once installed on the car we had to find a place to mount the 1995 Corvette ECM, which normally goes on a bracket near the brake booster. The solution is shown above, which unfortunately hides some of the sexy machined bits in this new, dual MC manual brake setup.

We did not want to chuck out the ABS system so we plumbed the return lines from the ABS pump into a Y-fitting that fed back to both master cylinders. This allowed us to keep the ABS functional.

The Tilton balance bar adjustment knob was mounted to an aluminum panel on the dash that also holds the Traction Control switch (it defaults to off now). We initially tested this new setup on the street, and quickly changed master cylinder bore diameters to get more braking force. Even using the best hydraulic ratio formulas you often have some trial and error - we were close, but needed one more iteration. The pedal effort is firmer than before (no vacuum assist) but the pedal travel is perfect and heel-toe is still easy. We then needed to test the car on track to prove it...


During this brake master upgrade period we also made some other small changes to the Corvette, to make it more reliable on track as well as to clear up any TTC class legality questions.

Earlier in the year, as we were fighting brake master cylinder issues that we couldn't diagnose easily, we threw some hastily made brake duct inlets and backing plates on the front of the car. That was when we briefly ran the car in TT2 class, which has no aero restrictions. The easy place to add the brake cooling air inlets was under the front nose. Because this is not exactly a good high pressure spot I decided on some vertical panels (see above) on the outside of these 3" round vents, to keep air from spilling away laterally from the inlets.

After some discussion with two different NASA race directors it was felt this vertical plane we added was in "a grey area" that could be protested, and someone could argue this deflector as a "canard" or "air dam". No, these didn't provide any downforce, and actually probably added a little lift, but they look like canards and the NASA rule book doesn't define terms like "canard"... its all up to the rules maker or protest judge to interpret the rules however they see fit. So to remove any doubt, we redesigned these brake duct inlets and removed the potential brake cooling "canards".

These plastic NACA ducts had an identical 3" hose connection and they were, in fact, much easier to install than the work needed to fabricate the "canards" and and brake duct inlets we had used before. Are they as effective? Hard to say without some very detailed testing, but these were deemed TTC legal without any doubt (or points) by the same race directors, so they went on.

A fire proof Nomex shift boot and aluminum mounting base were then added. We use this Joe's Racing shift boot kit on many builds, dating all the way back to our Alpha E36 LS1 car back in 2006. This boot goes over the old rubber transmission tunnel boot that was now 25 years old. This Nomex boot added a layer of noise, exhaust, and fire sealing to the stock transmission tunnel.

continued below
Veteran Member
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09 Nov 2016 06:54 PM
continued from above

I had noticed a bit of heat on my right leg in long stints so Brad added the thermal / reflective DEI material to the trans tunnel (see below), which is adhesive on one side. This has a layer of fiberglass insulation underneath the infrared reflective layer on top. We use this DEI insulating material on all sorts of cars to shield passenger areas or things like fuel lines from exhaust heat.

Around the same time as these things were going in I ordered another pair of the ZR1 / GM export flares for the C4 chassis as well as an ALDL connector (looks like OBD-II connector).

After a couple of tries at ordering via part numbers we finally received the correct ALDL connector for the 1994-1995 "Pre-OBD-II" connector port.

That was wired in to the ECM at the computer, then the connector mounted to the side of the dash on the passenger side. This port will help with tuning in the future, as well as checking CEL codes.

SCCA Club Trial & PDX, MSR-C, May 8, 2016

The next event we could sign up for that allowed us to test the brakes was this SCCA Club Trial and PDX event at MSR-Cresson. The weather was pretty poor and it rained off and on that day. Somehow we got almost no pictures of the two cars we brought, and the video camera I brought had a dead battery, so I got no video. I did get some dry laps in several sessions and the brakes were rock solid.

This was a combined PDX (HPDE) and Club Trial (Time Trial) but they didn't post any results. I asked for my times recently and they gave them to me - best of 1:24.3 in traffic. Out of 26 in Club Trials the Corvette posted the 3rd fastest, out paced by a Wolf (prototype) and TT3 M3. I ran a bunch of 1:24 and 1:25 lap times that day. The SCCA Club Trials events here aren't quite like what NASA runs, and the field has "a full range of talent". So traffic with 26 cars on 1.7 miles was as bad as you could expect. It was cold, rainy, cruddy weather. Still, I ran the car in 4 sessions and the brakes felt perfect.

I instructed that day and rode through with 3 different people, including Brad from Vorshlag in 2 sessions, an S550 Mustang racer for 2 sessions, and Amy for a session. Made good progress with my two PDX students and Amy dropped 4 seconds per lap in the 330 after some coaching. She was on the 245mm Dunlop street tires so the lap times she ran we're relevant to our times on Hoosiers.

I had that "Brake... Brake... BRAKE!" moment riding with Brad on one lap, hehe!

I didn't want to abuse the fresh Hoosier R7s so after fighting traffic most of the day I skipped 2 sessions and put the Corvette back in the trailer after confirming that the pedal effort was good, the balance worked, and the brakes were reliable.

I had planned on racing the car in the next few NASA race weekends but that just didn't ever happen. After the car was painted it was just too damn pretty...


After this May test event the car sat for a week then I decided to skip the NASA @ Hallett event in June and get a jump start on the paint work I felt the car needed to be able to sell.

The first step was to remove all of the decals from the car. Brad, Jon and I took turns and used low setting on the heat gun to soften the adhesive and pulled each one off without issue. Well, except the driver's door, which was entirely wrapped. It had some paint damage when we bought the car so Jon had wrapped that entire door in white film. More paint pulled off as this sheet was removed - Not a worry as this entire door would get reworked professionally at Heritage.

We pulled all of the rear plexiglass hatch off first, then the roof skin. This roof panel was black but I wanted to see it in white, so that would be prepped for paint work by Heritage.

Our local glass guys at Titan came by to remove the front windshield, which waited in my office for 2 months during the paint work.

Then the side view mirrors came off, padding from the cage was removed, seat and ballast box were unbolted, and all the nets came out. We cleaned the car and loaded it into the trailer for the trip to Heritage in Sherman, Texas.

Because this was a super busy time for them - 2 hail storms this Spring have had the body shops for 100 miles loaded up all year - I told them this was no rush. This way they could take their time and fit this admittedly lower paying paint job in between more lucrative insurance hail work.

The front bumper cover was never pretty but they managed to rework the nose nicely. This portion of body work made a huge difference in the end and I'm glad they spent the hours there.

The driver's door was a donor from another C4, installed many years ago, and it had existing damage and didn't match the rest of the car. They still managed to rework the fiberglass skin and get it looking smooth as glass before paint.

The rear bumper cover also needed some love, but they got it sanded down, smoothed out, primed and ready for paint.

The roof panel was sanded and smoothed, then primed before paint. Many hours were spent smoothing the hood and other fender panels, and of course the ZR1 export flares were bonded to the fiberglass, reshaped, smoothed, and integrated before being primed.

The roll cage took many hours to sand, wash, tack and prime, then paint. The interior and cage were painted separately from the body, but both received several base / clear coats of Siemens paint in GM Arctic White - which has no pigment, just white base. It is the brightest white made and it really POPS when you shoot it with a high gloss clear.

I picked the car up in mid August 2016 and was blown away. It looked... way nicer than I had hoped for. The price was less than it should have been, but still a good chunk of cash. I had the car painted to help increase the resale value and I think we got more than we bargained for...


Pictures simply do not to this paint job justice, and the pictures look GOOD. On a sunny day the brightness of this car is dangerous... #DANGERZONE

After getting a few shots of the freshly painted interior and exterior outside, we brought the Corvette in for the final list of updates.

I had a few things listed that I felt were necessary to "complete" my vision of this project.

That open "storage cubby" area behind the seats always bugged me, so I asked Donnie to make an aluminum panel to cover this and match the flat rear deck floor height. With some fiberglass-specific nutserts added the panel can be unbolted quickly for access to the ABS hydraulics behind the driver's seat. There's room for the battery on the other side but we decided against relocating that for now.

continued below
Veteran Member
Veteran Member

09 Nov 2016 06:55 PM
continued from above

The passenger floor always bugged me with its bumpy OEM shapes so I asked Donnie to make a pattern and then make a 2-piece false floor for this side. The front section can unbolt and the rear section sits under the weight box. Looked good.

Ryan made the reinforced false floor for the driver's side, which you step on to get in and out of the cage on that side. We will add grip tape for the buyer when they arrive to pick it up - just showing off the shiny aluminum for now.

The gaping hole in the passenger side of the dash was where the factory airbag was located, which was removed long ago. The open expanse looked awful and I wanted an aluminum dash cover to be built on that side. The marked up picture (above left) was all Ryan had to go on.

As usual Ryan thought farther than I had on the design and made it a 2-piece assembly. The upper portion mounted to the dash bar with rivets along two seams - bolts on the leading edge would be inaccessible with the windshield reinstalled. The lower section was removable with bolted hardware and nutserts installed into the upper section and along the sides.

Of course you don't want shiny aluminum up by your eye line for glare reasons, so these two panels were removed and painted with many coats of texture black paint. Many coats. The picture above right shows this in place before the windshield was reinstalled, but the vinyl portion of the dash had some conditioner sprayed on to soak into the stock material, which was later buffed off to a dull haze.

As well as the masking was done during the paint job, there was a hint of overspray in some areas and a couple of spots at the cowl we told them to leave in the stock black. These areas needed some prep and touch-up, so Brad masked off the freshly painted bits and prepped the areas that got some semi-gloss black paint.

Even the underside of the hood was cleaned and detailed, with the OEM colors and plastics shining like the day it rolled out of the factory. The difference here was amazing, but ate up 8+ hours of cleaning, prepping, painting, unmasking, and more cleaning.

After detailing the underhood area, the Corvette looks better than new, without a hint of over-spray and just enough gloss on the plastics to make my inner neat freak happy. This damn thing is too pretty for me to race now.

One of the things I debated for weeks on was over reinstalling the quick release fire bottle or adding a full fire system. It was deemed more costly and not what some people want, so I will leave a fire system up to the next owner. This is all the car needs to go Wheel to Wheel racing, by the way. Well that and updated belts (they are FIA Cobra/Schroth 6-point belts, but expired). The original reinforcing plates were shined up and installed, then the Drake quick release bracket and HalGuard 2.5 pound fire bottle were put back in place on the tunnel.

The stock steering wheel with the airbag removed was always a HUGE eyesore, and it made for a cumbersome ingress/egress with the cage installed. The diameter was so large that it blocked my sight line to some of the factory gauges.

I ordered the MOMO Model 88 in 350 mm diameter, and initially got it with the wrong 6-bolt hub adapter (p/n 2702, for GM telescoping column). We figured this out quickly and reordered the MOMO 6-bolt steering wheel hub adapter, part number 2401. This is the correct number for a C4 Chevrolet Corvette with standard GM tilt column, which we kept intact as it makes for easier adjustment for different drivers.

The new wheel really made a big difference, right? We had originally looked at adding a quick release steering wheel adapter but with the smaller diameter wheel and the tilt column its actually pretty easy to get into and out of the car with the steering wheel attached. I will leave a quick release up to the next owner, as these come in a variety of styles, thicknesses, quality levels, and prices.

Of course the rear hatch, the seat, the belts, nets, and SFI padding were all reinstalled. Some sections of wiring harness were secured and tucked better. All sorts of little odds and ends were made perfect before the final "for sale" pictures were taken. This was both fulfilling and painful. On one hand I loved to see the C4 finished like I had always envisioned. On the other I knew I'd never get to race the car again - it was just too perfect now.

For now this works, and the interior looks really finished, and it better shows the work we do. Unfortunately it is with a car that most folks don't associate with Vorshlag, and that's where the problem lies...


After all of this work over the past 2 years - getting the car fast, reliable, safe and looking good - it is time to sell it. Why? Like I said, this C4 Corvette isn't really a car that we see all that often at our shop. Maybe its the labor rates we charge, or the lack of competitive C4 race car entries right now, but this car isn't really representative of the customer work we see. And I need to be racing in the types of cars our customers own and bring to us. Like how a new BMW dealership wouldn't field a 25 year old Honda race car, you know?

Would I prefer to keep this car and race it? YES! Its one of the nicest cars I have ever owned, now that it is finished and painted. Damn the "marketing", I'd love to run this car in 2017 in TTC class or even TT4 with a few changes. But being a small business owner there are always expenses I have to plan for, and this car needs to fund some purchases that I have to do to keep Vorshlag moving forward.

It really sucks how these things happen... our E36 LS1 Alpha car was really fast right before we sold it, but it had to fund many things in our business in 2009 when it was sold. Likewise in 2015 when we sold our TT3 Mustang. I damn sure wanted to keep it, but that sale paid for a big chunk of one of our new CNC machines, which the business really needed. This C4 has a lot of time and money tied up into it and with as clean and perfect as it is now, it would be crazy for me to run it another season.

This car is ready for a racer to jump in and go to the track today. Be it Time Trial or even Wheel to Wheel (with 2 small updates), it is ready to go and do so reliably. I put this For Sale Page up this week and I hope you go there and look at all of the pictures we have there. The price might seem high to some but I couldn't build another one like it for twice the asking price. That's just the reality of a fully prepped race car built by professionals - quality costs money. Any help you readers can do to spread the word is appreciated. I am sharing this same link on Facebook as well.


It is going to be tough to say goodbye to Project #Dangerzone, but hopefully someone will appreciate all the work we have done and buy this C4 soon.

Once it is sold I will update this build thread and hopefully share what we have planned with those funds - its a big step for our business, if I can make it happen. Until then this Corvette will wait in our shop until it finds its new owner.

Terry Fair - www.vorshlag.com
Veteran Member
Veteran Member

27 Apr 2017 12:49 PM
this is a exampleProject update for April 27, 2017: Not much to share for the past few months. We've tidied up a few loose ends and put the car for sale on an eBay auction. Let's catch up.


After my last post I had the crew finish up a few things that weren't 100% perfect. One of the false floors was re-done in aluminum and it now looks great.

One of my guys re-fixed the oil pan gasket and its finally perfect. Brad did a final clean-up on the Corvette and then I towed the car to my home shop, where it has been resting...

There it has stayed while I got busy doing other things. We also found a lot of spare parts for the car when we moved it out of Vorshlag: new brake lines, belts, hoses, weatherstripping, a poly suspension bushing kit, and spare rotors, calipers, and another matching set of 17x9.5" SSR wheels. It all goes with the car!

Last year I had put up a classified ad on the Vorshlag website, then we moved our website and all of the old links went away. I finally re-did that last week and made a Cars for Sale page as well - which has several Vorshlag cars (some completed and some "donor chassis") as well as a few customer cars we built.


I wasn't in a huge hurry to sell the car as I was still unsure about our other shop race car's future - this 2001 BMW 330Ci. It was struggling to win in 2016 and I had some doubts as to its ability in TTD class for 2017...

Well we finally spent the time needed to add power to this BMW and in 2017 it has been breaking TTD track records each time it goes out. Still 2+ seconds off the TTC Corvette's times, but that's to be expected. So since we had a a new "record breaker" we just recently decided to step up the selling game on the C4.

Yep, today is a big day on project #Dangerzone - I just launched the 7 day eBay auction. Low reserve, lots of bids in the first few hours. We'll see how this goes.

Also have my house for sale (need more land to build a bigger shop on) - which is another thing that has been keeping me busy for the last couple of months, long with launching a 2nd business and running Vorshlag.

Long story short - if you have anyone you know that might want this beautiful race car, please send them the auction link! Its legal for Vintage racing this year, too. I will update this thread after the auction ends.

Terry @ Vorshlag
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