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Last Post 14 Jan 2015 01:04 PM by  OZMDD
C5s in STU?
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85rx-7gsl-se
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04 Sep 2013 08:50 AM
Posted By gary p on 03 Sep 2013 09:46 PM
Posted By 85rx-7gsl-se on 03 Sep 2013 05:11 PM
I am just trying to figure our how limiting a 2wd car to the same tire size as an AWD with what I would assume is roughly similar weight/power is anywhere near fair?

And I'm trying to figure how letting a car with similar weight,  much lower CG, much better F/R weight balance, and short/long arm suspension at all 4 corners have 40mm more tire width than the Evo and STi is anywhere near fair. 


So I guess your AWD means nothing? lol
gary p
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04 Sep 2013 09:30 AM
Posted By 85rx-7gsl-se on 04 Sep 2013 08:50 AM
Posted By gary p on 03 Sep 2013 09:46 PM
Posted By 85rx-7gsl-se on 03 Sep 2013 05:11 PM
I am just trying to figure our how limiting a 2wd car to the same tire size as an AWD with what I would assume is roughly similar weight/power is anywhere near fair?

And I'm trying to figure how letting a car with similar weight,  much lower CG, much better F/R weight balance, and short/long arm suspension at all 4 corners have 40mm more tire width than the Evo and STi is anywhere near fair. 


So I guess your AWD means nothing? lol
It means it will not spin wheels on acceleration on dry pavement. That's it.  When the turns come (and they tend to have some of those in autocross) a "boost buggy" might as well be a Corolla with 300#s of ballast. 
85rx-7gsl-se
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04 Sep 2013 09:46 AM
I am still curious if anyone has results of C5s on street tires to demonstrate superiority to boost buggies in STU trim?
edfishjr
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04 Sep 2013 04:07 PM
Posted By gary p on 03 Sep 2013 09:46 PM
Posted By 85rx-7gsl-se on 03 Sep 2013 05:11 PM
I am just trying to figure our how limiting a 2wd car to the same tire size as an AWD with what I would assume is roughly similar weight/power is anywhere near fair?

And I'm trying to figure how letting a car with similar weight,  much lower CG, much better F/R weight balance, and short/long arm suspension at all 4 corners have 40mm more tire width than the Evo and STi is anywhere near fair. 

 

Lots of theory, but we have some recent test results that indicate how hard it will be to get a C5 competitive in STU: Strano, Junior and Newman in Newmans C5 on Rivals couldn't get within 2s of their times on the A6's on a 45s course. That's 2.67 seconds on a 60s course that ST preparation has to improve the car to make it competitive in STU, much less dominant, based on the present equal PAXs. Ask yourself if you believe that can happen. I've been driving a C5 on both street tires and A6's. I have a very hard time believing it.

JRHO is on record as saying he would choose the C5 and everyone has a lot of respect for his ST setup and driving skills. I wonder if he is so sure after the Newman test?

hklvette
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04 Sep 2013 05:03 PM

I think you and I have talked about this, but do Rivals work properly with an alignment setup for A6s?  That may gain you some back by itself, but two seconds on a 45s course may be a bridge too far.  Stiffer suspension only gets you so much especially on a car already well setup from the factory.  Only thing left is more power, which isn't much use except when the course goes straight.

edfishjr
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04 Sep 2013 06:54 PM
Posted By hklvette on 04 Sep 2013 05:03 PM

I think you and I have talked about this, but do Rivals work properly with an alignment setup for A6s?  That may gain you some back by itself, but two seconds on a 45s course may be a bridge too far.  Stiffer suspension only gets you so much especially on a car already well setup from the factory.  Only thing left is more power, which isn't much use except when the course goes straight.

When I was running street tires I had to have more rear toe-in, very soft-set shocks, lowest possible rear tire pressure and zero rake in order to put power down and control power-on oversteer coming out of corners as compared to the standard "Strano" setup, or what I think is the "Strano" setup for C5s. So, I would definitely agree that Newmans car, setup for A6s, was probably not optimum for a street tire, in general. (I have no experience with Rivals in particular... I used RS3s and AD08s back then.)

After arriving at the more optimum setup for street tires, I then began running A6's and evolved the setup away from the above and back to my original "Strano" setup. The key point is that my experience mirrors the Newman test... the A6 setup was way more than 2s faster than the best I could do on streets and the big difference was in braking and accelerating while turning. I had to brake much sooner on streets and get on the power much later and slower coming off a corner. Yet, steady state lateral Gs were not much different per Traqmate: typically 1.2 for A6's and 1.1 for streets on asphalt, for instance, which also tracks with the Newman test report.

gary p
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04 Sep 2013 08:12 PM
Don't forget that the STU boost buggies will lose some power next year when they can no longer run E85. 
murphyslaww
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04 Sep 2013 10:43 PM

Any reason no one is comparing the C5's to the E46 M's that were competing ?

Would a C5 be a whole lot different than an E46 M on 285's ?

They seemed to be about a half second to a second off the boost buggies.

splash
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05 Sep 2013 02:09 AM
Posted By hklvette on 04 Sep 2013 08:48 AM

Okay.  Next question: Would the situation be better if the AWD cars got 285s?

Well, it sure wouldn't hurt...

Another thing to remember is that the boost buggies have been beaten at nationals already, by an E36 M3 that is limited to 255/265 tires by default. Sure, it took a course design more favorable to it, but an E36 M3 does not have a Corvette's CG, a Corvette's power and torque, and can't fit 285's.

One problem we are having, doing all this theorizing, is that only recently have there been a lot of top-tier ST* tires in sizes over 255. Now, you can get decent ST tires in 275/285 widths. There also hasn't been a reason to buy them since they approach Hoosier costs (sometimes exceed it), and IMO, only the E46 M3 had a shot at being able to use them. I've never seen anyone really try a STU E46 M3.

I am actually all for finding more cars for STU, if only to break up the "spec-rally-car" nature of it. But, this would be FAR from the first time the abilities of AWD (especially on concrete) have been over-compensated for. There is already no reason to show up in STX with a WRX anymore, I'd really like to see that not happen to STU as well. Yes, AWD is worth something, sometimes, but it isn't worth everything, every time.

Put not so succinctly, if the C5's get into STU, I'd likely move to an automatic one, bump the limiter up, go with taller wheels/ 285 tires, and try to shift the powerband to the right a bit. The only impediments to me after that would be rain, and MAYBE courses with frequent slow 180's followed by straights...


hklvette
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05 Sep 2013 11:42 AM
I'm curious to see how much more rev-limit the stock LS1 valvetrain can handle. The LS6 has a pretty stout factory setup, with stronger springs to deal with the increased lift and rpm of the LS6 cam, and it could take more rpm than stock for an extended period of time. I don't recall the LS1 springs being able to do that for very long. I won't be the one to try and get more rpm, that's for sure. Since springs and bars are open in ST*, a base automatic would be the one to start with because autos with Z51 got a 3.15 diff instead of the base 2.73.

More food for thought on the auto: How much converter slip is there when the engine reaches 6k rpm at full power? That may influence end-of-straight behavior between the M6 and A4.
85rx-7gsl-se
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05 Sep 2013 01:29 PM
So the concensus is auto over manual for the c5 in STU trim?
edfishjr
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05 Sep 2013 02:00 PM
Posted By 85rx-7gsl-se on 05 Sep 2013 01:29 PM
So the concensus is auto over manual for the c5 in STU trim?

I'd have trouble giving up the horsepower to run an automatic.... you'd give back most of what you got with a tune, intake & exhaust. I guess the thinking is that somehow the gear ratio can be greatly improved? Can the shift speed be improved? That would require an internal change to the shift valves, wouldn't it? A lot of shifting between 1st and 2nd in an automatic is gonna kill you, I'd think. Or is the idea to always run in 1st?

Seems to me to make a C5 work in STU you must:

1) fatten the mid-range torque as much as possible. The gearing problem with the standard C5, in my opinion, is how relatively poorly it accelerates from 25 to 35 mph in 2nd gear. At 35 the torque starts coming on. This is going to require some real tuning and testing, as few aftermarket parts/systems are designed to do this. Everybody chases headline horsepower.

2) Get every bit of the torque down to the ground when coming off corners. I could never get my car to do this well on street tires, but I'm just a beginner at car setup. You might even have to remove the rear sway bar, as one person opined.

3) lower the heck out it and increase camber to further improve the already good sweeping ability (getting all 4 tires to grip even better) without totally ruining the handling. I assume that those who really know what they are doing can get this done in STU.

4) Throw the seats into the nearest field and set fire to them, just to improve your attitude.

And I think hklvette is right, there isn't much headroom to increase the rev limit above the 6200 RPM limit it comes with, but I'm sure some will do it. Even 200 RPM might be very useful within a broader scheme.

hklvette
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05 Sep 2013 02:49 PM
Posted By edfishjr on 05 Sep 2013 02:00 PM
Posted By 85rx-7gsl-se on 05 Sep 2013 01:29 PM
So the concensus is auto over manual for the c5 in STU trim?

I'd have trouble giving up the horsepower to run an automatic.... you'd give back most of what you got with a tune, intake & exhaust. I guess the thinking is that somehow the gear ratio can be greatly improved? Can the shift speed be improved? That would require an internal change to the shift valves, wouldn't it? A lot of shifting between 1st and 2nd in an automatic is gonna kill you, I'd think. Or is the idea to always run in 1st?

Seems to me to make a C5 work in STU you must:

1) fatten the mid-range torque as much as possible. The gearing problem with the standard C5, in my opinion, is how relatively poorly it accelerates from 25 to 35 mph in 2nd gear. At 35 the torque starts coming on. This is going to require some real tuning and testing, as few aftermarket parts/systems are designed to do this. Everybody chases headline horsepower.

2) Get every bit of the torque down to the ground when coming off corners. I could never get my car to do this well on street tires, but I'm just a beginner at car setup. You might even have to remove the rear sway bar, as one person opined.

3) lower the heck out it and increase camber to further improve the already good sweeping ability (getting all 4 tires to grip even better) without totally ruining the handling. I assume that those who really know what they are doing can get this done in STU.

4) Throw the seats into the nearest field and set fire to them, just to improve your attitude.

And I think hklvette is right, there isn't much headroom to increase the rev limit above the 6200 RPM limit it comes with, but I'm sure some will do it. Even 200 RPM might be very useful within a broader scheme.


I think the thought process behind the A4 is that it has a longer 1st gear than the M6, but is shorter than the M6s 2nd gear.  Note: This only applies with the 2.73 gears.  The 3.15s performance gears erase that advantage

As for low to mid-range torque.  The '01+ could use more, and the pre-'01s REALLY need more to get use out of 2nd gear.  Pfadt is supposedly going to have tri-y headers out soon to help with that.  QTP used to make some, but don't anymore.

+1 for ditching the factory seats.  Recaros on sliders for me, please!

The Nebulizer
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05 Sep 2013 02:51 PM
Posted By splash on 05 Sep 2013 02:09 AM
Posted By hklvette on 04 Sep 2013 08:48 AM

Okay.  Next question: Would the situation be better if the AWD cars got 285s?

Well, it sure wouldn't hurt...

Another thing to remember is that the boost buggies have been beaten at nationals already, by an E36 M3 that is limited to 255/265 tires by default. Sure, it took a course design more favorable to it, but an E36 M3 does not have a Corvette's CG, a Corvette's power and torque, and can't fit 285's.

One problem we are having, doing all this theorizing, is that only recently have there been a lot of top-tier ST* tires in sizes over 255. Now, you can get decent ST tires in 275/285 widths. There also hasn't been a reason to buy them since they approach Hoosier costs (sometimes exceed it), and IMO, only the E46 M3 had a shot at being able to use them. I've never seen anyone really try a STU E46 M3.

I am actually all for finding more cars for STU, if only to break up the "spec-rally-car" nature of it. But, this would be FAR from the first time the abilities of AWD (especially on concrete) have been over-compensated for. There is already no reason to show up in STX with a WRX anymore, I'd really like to see that not happen to STU as well. Yes, AWD is worth something, sometimes, but it isn't worth everything, every time.

Put not so succinctly, if the C5's get into STU, I'd likely move to an automatic one, bump the limiter up, go with taller wheels/ 285 tires, and try to shift the powerband to the right a bit. The only impediments to me after that would be rain, and MAYBE courses with frequent slow 180's followed by straights...

 


Splash, I competed with you a few times in STU in my e46 M3. I gave STU a shot (6 NTs and Nats) for a few years and finally gave up. I am convinced the e46 M3 is nearly a second off the STi/Evo. I'd say the e36 M3 is slightly better off as it benefits from being skinnier and lighter. The extra horsepower of the e46 M3 is not very usable and I am not convinced 285s are really that valuable in putting power down. The C5 has benefits over the e36 M3, but it is also quite a bit wider (like the e46 M3), so it won't have the slalom advantage the e36 M3 has.

Also, Tristan outdrove the STU field when he won in the e36 M3. The car was a hinderance that he overcame.

My guess is the C5 would be a pretty good fit in STU.

splash
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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.
85rx-7gsl-se
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05 Sep 2013 07:18 PM
So would you propose a creation a new class above STU instead for the Corvette? Or just leave them without a place to place in ST* classes?
85rx-7gsl-se
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05 Sep 2013 07:20 PM
Double post
sjfehr
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05 Sep 2013 07:57 PM
Posted By 85rx-7gsl-se on 05 Sep 2013 07:20 PM
So would you propose a creation a new class above STU instead for the Corvette? Or just leave them without a place to place in ST* classes?

STP has been suggested numerous times as a higher ST class for high performance cars like Corvettes and Porsches to play that are considered to be too fast for STU or STR.

 

Personally, I'd settle for camber plates in street class, though.

edfishjr
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05 Sep 2013 09:58 PM
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.

Using the Turn Zero gearing calculator, 3.06 first gear and 2.73 axle ratio, if you go up to a 285/35-19 you can get to 59.3 mph at 6400 RPM, not accounting for torque converter slip. So far, I'm not seeing a way to get to 63-64 as you desire. Edit: I'm using their tire deformation feature, which gives only 57.1 mph in 1st, stock, at 6200 RPM.


splash
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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.
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