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Last Post 14 Jan 2015 01:04 PM by  OZMDD
C5s in STU?
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edfishjr
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06 Sep 2013 12:11 AM
Posted By splash on 05 Sep 2013 11:00 PM
I don't know that I'd waste a 200rpm bump. Mine is bumped to 7600 from 7200 and seems to be solid on a 180K mile motor. But then, it isn't a Chevy ...

Has anyone also looked into superseded parts that could fix any potential reliability issues from a limiter bump? Perhaps the LS6 rockers are standard replacements for LS1 by now... Hey, it's a longshot, but not unheard of.

Also, the Rival and RS3 come in a 285/35-20. Note, I'm not counting costs, just that it can be done. I learned a long time ago that you simply cannot legislate what one will spend to win. Barring fitment issues, there's an extra inch of diameter right there.

Also, what about running 285/30-18 on the 6-spd car in 2nd? At 24.8" diameter, it's likely the shortest tire size that would work.

The extra 500 rpm in the LS6 motor are due to the lighter, sodium-filled valves and very different springs... different material, different wind, etc. which produces quite a bit higher seat pressures. Neither of those components can be legally put in the LS1. The LS6 cam(s) accelerates the valves much faster than the LS1 cam(s). I've read testimony that 6400 has been ok in stock motors in tracked cars, but the consensus is no more than that without changing the springs and, if the car is pre-2001, the rod bolts. (The rod bolts got stronger in 2001, a change that was mandated by the Z06 and they just made it common.) Maybe for an autocross car you could push it further, if you weren't worried about rebuild cost if it came apart. Juriga (chief engineer) was quoted as saying the LS6 valves float between 6800-7000 RPM. I can only assume the LS1 would be lower. (One person claims valve float occurred at 6400 on his LS1 on the dyno. I'm not quite sure how you know that for sure.) Juriga also said that both engines could be revved to 7000 and "not immediately put a rod through the side of the block." I guess it all depends on your definition of immediately!

I have, in fact, run the short 285 A6s on my car, the lower-torque 2000 model year. Very nice increase in 2nd gear responsiveness, but abandoned it as it wasn't faster overall than running 315s in Stock class, at least on Nationals-type courses. (I was talking to Savini at Wilmington and found out he had come to the same conclusion.)

It didn't occur to me to go to 20" wheels. At 6600 rpm that gets you to your 63-64 mph in first with the automatic.


splash
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06 Sep 2013 01:03 AM
I wonder if you could get away with that 6600 limiter, knowing that the LS6 has to deal with both, the higher limiter, and the more aggressive cams. Then again, it may float by then.

My thinking with the manual is that the shorter tire might bring the torque into a usable range without being "too much" for the tires. In all honesty though, I don't know what a stock diameter 285 street tire would be like in slower corners to compare to. It makes sense that the short 285 might not compare well to a 315, even though the 315 is taller, but only because those are Hoosiers. Limit everything to 285 street tires, and you need to match the diameter to what is "usable" with the torque band you have.

By "usable", I'm talking about effective use. Similar to why the newer V8 Mustangs are going to STU from STX. You'd think they'd be more competitive in STX, but a 420hp Mustang on 265 street tires is comical insofar as the amount of throttle you just can't use. In STU, they get to use 285 tires to help with that (at least a bit). I'd imagine a Z06 would be the same on 285 street tires, but I'd also imagine that, if this is indeed the case, then the "bad gearing" and less torque of the manual base C5 could be exactly what is needed to make it usable. There is definitely a "window" between bogging the engine and frying the tires. I just know that there is anywhere from the 285/30-18 to the 285/35-20 rear tire diameters with which to find it. (24.8" to 27.9")

Also, noting the 350Z leading STR at the moment... Still think they need 30mm more tire and put in STU?

Oh, and I'm curious. How do you tell a base C5 from a FRC?
hklvette
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06 Sep 2013 08:42 AM
Posted By splash on 06 Sep 2013 01:03 AM
I wonder if you could get away with that 6600 limiter, knowing that the LS6 has to deal with both, the higher limiter, and the more aggressive cams. Then again, it may float by then.

My thinking with the manual is that the shorter tire might bring the torque into a usable range without being "too much" for the tires. In all honesty though, I don't know what a stock diameter 285 street tire would be like in slower corners to compare to. It makes sense that the short 285 might not compare well to a 315, even though the 315 is taller, but only because those are Hoosiers. Limit everything to 285 street tires, and you need to match the diameter to what is "usable" with the torque band you have.

By "usable", I'm talking about effective use. Similar to why the newer V8 Mustangs are going to STU from STX. You'd think they'd be more competitive in STX, but a 420hp Mustang on 265 street tires is comical insofar as the amount of throttle you just can't use. In STU, they get to use 285 tires to help with that (at least a bit). I'd imagine a Z06 would be the same on 285 street tires, but I'd also imagine that, if this is indeed the case, then the "bad gearing" and less torque of the manual base C5 could be exactly what is needed to make it usable. There is definitely a "window" between bogging the engine and frying the tires. I just know that there is anywhere from the 285/30-18 to the 285/35-20 rear tire diameters with which to find it. (24.8" to 27.9")

Also, noting the 350Z leading STR at the moment... Still think they need 30mm more tire and put in STU?

Oh, and I'm curious. How do you tell a base C5 from a FRC?

Working backwards from the bottom:

An FRC looks just like a C5 Z06, but doesn't have the rear brake ducts, shorter ratio transmission, or LS6.  All of those are easy to find in impound if one tried to re-body a Z as a "FRC".

Does anyone know of back-to-back test to see how much difference wider tires really make?  Heat management plays a part, but beyond that how much is really gained?  I've seen tests where the same wheel was used for both the narrow and wider tires, but that isn't what I'm looking for.

For taller tires than about 26.6" (factory) height, you'd need some really stiff suspension to keep them from rubbing all over the bodywork.  With a lot of patience, a heat gun, and a fender roller it could be made to work in the rear but the front would be somewhere between difficult and impossible with tires over 26" and 285 width.

I don't know diddly about mustangs, but consider this about the C5Z:  Ignoring its superior powerplant, it would still do better since gears 1-4 are shorter in its transmission than the base trans.  This allows it to use 2nd gear with great effect at auto-x on slightly shorter-than-factory tires 285-265/35/18 vs factory 295/35/18.  The 18" rivals are just about perfect for it.

Higher limiter on LS1 is almost out of the question, unless you put a fresh set of springs on right before a big event and turned it up for that event only.  Even then its not guaranteed that you could get away with it.  Remember that pushrods demand a lot more of their valve springs than a comparable OHC setup due to the extra valvetrain mass, so each little increase in RPM is much more duty for the springs to cope with.  I just checked the parts catalog yesterday, and unfortunately the LS1 valve spring DID NOT get superseded by the LS6 spring, or any other spring for that matter.  I'd have done the swap for peace of mind, if nothing else.

85rx-7gsl-se
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06 Sep 2013 10:45 AM
Another way to tell if it is a FRC is does it have a trunk instead of a hatch lol
The Nebulizer
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06 Sep 2013 11:04 AM
Posted By splash on 05 Sep 2013 06:05 PM
^^ Right, and that is my point. IIRC, you ran Kumho XS's at the time... Why? I think it was about the only tire at the time that fit and was wide enough, right? Since nobody else has ever done particularly well on XS's, how much of that 1 sec do you think was from using the "wrong" tire? I don't know if you ever had anything else on it, but I'm pretty certain the XS was not even competitive against the RE-01, never mind the later Z1/RS3, or the current Rival/Z2.

Nowadays, The Z2, RS3, AD-08R, and Rival are all made in 275/285 sizes.

Oh, and my thoughts on the Auto C5 are to make the car do 63-64mph in 1st gear since it does 57mph in 1st stock. I know on my STI (mine has the shortest gearing), I can get to 63-64 in 2nd if I bump the limiter 400-500rpm and use a 1-inch taller wheel/tire package. An '07 STI can get to 63-64mph in 2nd and only has to do one of those (slightly taller 2nd gear, but worse rear diff). Knowing this about my car is why I don't buy the "bad gearing" argument for letting the C5 in STU. If I can fix it so that's it's tolerable, so can they.

Another thought with the C5 is to use the manual in 2nd gear, and see how much shorter a 285/30-18 is from the stock tire size, then tune it for torque, as far left as you can get. However, I still think the Auto is closer, and should provide plenty of torque to the wheels in 1st gear, hence my thought of tuning to the right on those.

The XS/285 was a great tire in the hot and dry. I'd say on par with anything else available a couple years ago. I also ran on the ultra pricey AD08/285 (no better than XS). RS3 and Star Specs were available in 275 sizes back then.

I've studied the M3 in that class as I really wanted it to work. There were several better drivers (Robert Irish, Jon Pomeranke, Brian Flannigan, Ken Orgeron, John something from Houston..., Terry Fair, etc.) that came to the essentially the same conclusion that the e46 M3 was a good second off (Irish and Pomeranke did side by side tests with a prepped M3 and mildly prepped STi and came up with 1.7 seconds - and immediately sold their prepped M3 and switched to an STi). The best reason seems to be that it is much wider and especially struggles to put the power down out of the turns. Both of these issues are present for the C5, but the C5 does have clear advantages over the e46 M3. I think enough advantage to move it to competitive with STi/Evo, but not be dominant.

However, a simple rule change (that many in STU would likely welcome) could easily close any gap that could arise. STi/Evos have been held back to try to make the M3s competitive. I'd say let the C5 in and then feel more free to remove some of these limits (Turbo, tire size especially). I'd ideally like to see tire/wheel size limits removed entirely from ST* - run what fits in or under the fenders - no cutting, no bending. No one is seriously campaigning an M3. Even Tristan knew it was not a great idea with the e36 M3 and moved on to a better classed car.

I am really curious about an earlier question of how much faster would an STi/Evo be with 285s.

splash
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06 Sep 2013 01:14 PM
I really wasn't concerned with a Z06, but rather a FRC vs a base C5. If it really is as simple as the FRCs have trunks and the base C5s have hatches, then that makes it simple...

I wasn't worried about the front, because you can run whatever 285 fits up front. Unlike my car, the front and rear tires need not be the same diameter. It's the rear tires that determine any gearing change.

I tried the Kumho XS and it was a disaster. It took a co-driver, 3-minute splits, and a 90+ degree sunny day to get them hot enough to work as well as my RE-01's did. The RS3 is also a heat preferring tire, in that they don't work well until warmed, but still not as bad about it as the XS. I never got to try the AD-08, as the Z1 and RS3 came out in my size and I centered on those two. Though I hear the new AD-08R is pretty good too.

The only thing holding me back on the 285's for the rally cars is a selfish reason. The EVO can fit them without raising or flaring. I can fit them up front, but the rear would have to be run higher/stiffer because they will stick out. To be honest, I would likely just run 285/30-18 up front and 245/40-18 out back (same diameter). You are likely never to find a test of 285s on the rally cars because the only classes that allow that also allow R-tires. The closest you will find is in a region that has an SMS-type class. We have one, but I've never seen a rally car with more than 255's on it so far. Since SMS is not national, you might have trouble finding someone that took it seriously enough to spend the money on 285-18's.
85rx-7gsl-se
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07 Sep 2013 10:45 AM
Just as a quick double check, the proposal to switch to 200 treadwear in ST did or did not pass?
edfishjr
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07 Sep 2013 02:26 PM

Posted By <span class='af-profile-name'>85rx-7gsl-se</span> on 07 Sep 2013 10:45 AM
Just as a quick double check, the proposal to switch to 200 treadwear in ST did or did not pass?

could be mistaken, but I don't recall any proposal to change ST tire specs.
85rx-7gsl-se
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07 Sep 2013 03:25 PM
Posted By edfishjr on 07 Sep 2013 02:26 PM

Posted By 85rx-7gsl-se on 07 Sep 2013 10:45 AM
Just as a quick double check, the proposal to switch to 200 treadwear in ST did or did not pass?

could be mistaken, but I don't recall any proposal to change ST tire specs.

It was from last year's May Fastrack:

http://scca.cdn.racersites.com/prod....pdf  Page 40

I am guessing no, but figured I would ask as I know the street proposal eventually ends up with a 200 treadwear limit. 

edfishjr
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07 Sep 2013 08:50 PM
Posted By 85rx-7gsl-se on 07 Sep 2013 03:25 PM
Posted By edfishjr on 07 Sep 2013 02:26 PM

Posted By 85rx-7gsl-se on 07 Sep 2013 10:45 AM
Just as a quick double check, the proposal to switch to 200 treadwear in ST did or did not pass?

could be mistaken, but I don't recall any proposal to change ST tire specs.

It was from last year's May Fastrack:

http://scca.cdn.racersites.com/prod....pdf  Page 40

I am guessing no, but figured I would ask as I know the street proposal eventually ends up with a 200 treadwear limit. 

Oh, that!  I don't think it ever made it to the proposal stage, just floated for comment. It was taken out to the alley, shot & buried in a shallow grave.

Of course, now it looks like it will be happen anyway as all the new summer tires go to 200TW as a default. But even Street gets to use the 140s another year.


85rx-7gsl-se
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07 Sep 2013 09:09 PM
I just ask as the tire I would likely run at first is 140 and I kind of doubt will change haha.
splash
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08 Sep 2013 12:13 AM
There's no need for that proposal anymore. Between our Street category and other sanctioning bodies, TW 200 is becoming the norm. The market will adjust on its own accordingly.
gary p
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21 Sep 2013 06:22 PM
Looks like this has been sent to the BOD for approval. Furthermore, looks like the FRC exclusion has been dropped (Z06 still excluded).
hklvette
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21 Sep 2013 09:30 PM
Posted By gary p on 21 Sep 2013 06:22 PM
Looks like this has been sent to the BOD for approval. Furthermore, looks like the FRC exclusion has been dropped (Z06 still excluded).

Hmmm...looks like the rails were greased a bit.  The last time the proposal was in fastrack, it said it wouldn't happen until 2015.  I'm quite excited to have an ST class to play in

splash
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23 Sep 2013 07:38 PM
FRC automatic, if there is such a thing...
hklvette
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24 Sep 2013 08:35 AM
Posted By splash on 23 Sep 2013 07:38 PM
FRC automatic, if there is such a thing...

There was never a factory automatic FRC.  They all came with the T56 and Z51.


85rx-7gsl-se
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24 Sep 2013 09:25 AM
While the FRC would be the car of choice, if I were to run I would likely be in coupe just to have a newer car.
AustinTX
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24 Sep 2013 11:02 AM
If I had to put a tire that didn't fit inside the rear fender of my STI, I would move on

Seems that much of the C5 concern is over gearing - is it difficult to do a 2-1 shift in the 30MPH range in the car?

John
gary p
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24 Sep 2013 11:51 AM
Posted By AustinTX on 24 Sep 2013 11:02 AM
If I had to put a tire that didn't fit inside the rear fender of my STI, I would move on

Seems that much of the C5 concern is over gearing - is it difficult to do a 2-1 shift in the 30MPH range in the car?

John
The gear talk is not about shifting, it's about how tall second gear is and how that "dilutes" the car's torque at autocross speeds.   It's not about what it does under 30, its about what it does from 35-65. 

AustinTX
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24 Sep 2013 12:19 PM
I'm looking at it similarly to how I look at courses in the STI.  I went to 3rd gear 4 times per run on the east course at nats this year, and I would probably drive the vette similarly between first/second gear if the transmission allows it.  In that case, the vette should have PLENTY of accelleration when driving in first most of the time.  You guys are way too comfortable with simply leaving it in 2nd 
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