This winter I plan on upgrading my ol' C4 a bit for next autocross season. The more i race it, the more I realize how bad the body roll is....

Car: 1992 6spd on Nitto NT05 tires. All shims pulled out for camber!
Mods: J55 brake upgrade with Hawk HPS pads in front, stock pads in rear. NOT a Z07 car, so I have floppy springs

Note: Car is daily driven, 15k miles a year at least.

I've been reading up on sway bars and I can't decide what to do. I don't race with SCCA so I don't care about classing at all, I just want the car to handle better.
I know 32mm front and 26mm rear is a common setup, but are those hollow or solid bars? Also, would it be okay to run bars that big on stock springs?

People with sway bar and autocross experience please speak up, thank you!!

 

those bars COME on springs from the factory. Depends on the package your car has...

Look up the C4 suspension chart. It tells of the different combos and whats on which yr. They are ALL available.
You need bushings and some solid mounts on certain things to make it feel solid. It will be not much fun on the street...so choose wisely. Mine is like a buck-board. It was ok when it saw the street RARELY....now its a DD and this set-up is miserable.

 

It is fine to have big bars and soft springs. A LOT of road course guys favor this setup. I'm not sure if the 32mm bars are solid or not. I HOPE they are. The 26mm solid would be too much IMHO paired with soft springs and only the Z07/Z51 30mm solid front bar. The 26mm rear bars are all solid, at least the factory bars.

You should consider upgrading to Z07 springs as well. I did and the difference was HUGE. CorvetteNutz has a 93 Z07 they are parting out. I got my setup off him and am very happy with it. Ride quality is a bit harsher but very livable.

Sounds like your brake setup is about perfect for auto-x. Same with the front alignment with stock bushings. I'm running negative 1.4 degrees in the rear for camber. About the same up front with stock bushings and all shims pulled out.

 

I have a 96' which has the softest springs ever on a C4. This last spring I increased my sway-bars to 29mm solid front (was 26mm tube) and 26mm solid rear (was 24mm solid) and they work very well together. This is as close to Z07 sway-bars as I could get with after markets. Both are made by ADDCO. The sway-bars don't change the ride as much as they do body roll. The ride comes from the springs and shocks mostly. This thing now handles like it's on rails and still has a smooth ride. A solid sway-bars is as stiff as a tube that is 2mm larger. So a 30mm solid is the same as a 32mm tube but weighs a little more. You can use either and get close to the same results.

 

Thanks for the responses guys! I'm wondering, how good is the Z07 setup? If I were to mimick the Z07 and get the same springs and sway bars, would it be worth it? Or would my money be better spent going with larger bars? This car is a daily driver, but I'm only 21 years old so I don't really care if the ride is a little harsh

Rubie, please tell me about your setup! I may want to copy it if you don't mind!

 

I've got a 32/26 setup with FX3 springs and I like it a lot.

 

My car is simply a FE1 FX3 car converted to Z07 specs.

Z07 Package had the following:
Z51 stamped Lower control arms with stiffer bushings (note these where NOT available as a service replacement ONLY came from factory, service replacements are regular non-HD bushings and SCCA Stock legal, as far as I know). I'm replacing my old control arms with NOS ones this winter.

FX3 Shocks, still on my car, next year will be Koni Sports.

FSK 90.1 N/mm front spring
NYU 57.2 N/mm rear spring

30mm Solid Front sway bar-Factory
24mm Solid Rear sway bar-Factory

J55 front brakes

My wheels are 17X9.5 91 Sawblades shod with 255/40/17 Dunlap Dizerra ZII's.

Alignment is as follows:
All front shims pulled and zero toe.
Rear is 1.4 degrees negative
Stock toe-in settings in rear.

That is pretty much it. My car is VERY stock. Will be more so after winter as I'm serious about running B-Street next season and doing at least 1 SCCA National event.

Proof in the pudding, this was a good day, and represents my better driving.

Look for Shawn Bauman in 17th PAX. My point is these cars are NOT slow, setup and driven right, they are flat haul ***. NOT a C5 or C6, but still pretty quick.
http://scrsolo.files.wordpress.com/2...ent03_pax1.pdf








While stiffer bars with soft springs work well at a road course. Most auto-x guys seem to like stiffer springs as well.

The Z07 works really well is a HUGE step over stock. The car was NIGHT and DAY after doing it. MUCH flatter cornering and more responsive.

There is a few setup tricks I've learned as well. For instance, lowering the front end is a good thing. Rear does not seem to matter. However, the lowering bolts you can get for the rear can be VERY useful at jacking weight off the RF corner onto the LF corner. Work for stock setup too, run the LR castle nut up tight, and get the RR castle nut right against the cotter pin or as low as you dare with the longer lowering bolts. I did this and it made a difference I could feel in turns to the right.

The sway bars are a nice thing to play with. With the huge 30mm front bar and RUBBER bushings you can place alignment shims between the halves of the mounts and change how quickly and how much the front bar effects cornering. I currently run 1 1/16" thick alignment shim under each part of the mounting halves in the front for total of 4. This took some understeer out but the car is still stable.

I'll warn YOU and others about running a 26mm rear bar and ONLY a 30mm solid front bar. Quite frankly I have NO idea how you would run this with the stiffer Z07 springs. I TRIED to run 1/8" shims under the front bar pursuing less understeer and the car Jacked=SNAP oversteer on ONLY the 24mm solid rear bar and STICKY STREET tires. Went back to 1/16" shims and all was ok. However, if I had the 26mm rear bar those would probably be GONE to keep the car stable. Even then I think the 26mm is TOO much for these cars with stiffer springs.

They might work with soft springs but NO way on hard ones.
FYI, BSP prepped C4's NEVER run those big rear bars. Seems most are like 22mm or smaller. All to keep the rear end in check. The rear roll center is too high and higher than the front, too much rear roll stiffness=Jacking=Snap Oversteer=Hard to control=Loss of confidence in car=SLOW.

You want the front to bite and the rear to follow.
SoloFast is the MAN when it comes to C4 stuff. He ran these cars for years at the top level and knows his stuff. His tricks/tips have been working for me.

How fast do you want to go? Also depends on how much $$$ you want to spend. Closer to stock is cheaper. I've considered running BSP however its too much $$$$. I'd rather setup a stock class car and run the crap out of it.

 

The 90' Z51 and the 91' Z07 both had 30mm solid front and 26mm solid rear sway bars so at least the engineers thought they were a good match. In 91' they also matched the stiffest Z07 springs ever made with them.

 

Ruby, another good post, thanks!

 

There are discrepancies within these charts.

http://www.corvetteactioncenter.com/...usp_chart.html

http://www.netmotive.net/articles/hib/c4/sustunch.pdf

However, SoloFast, was THERE. The 26mm rear bar was ONLY on the 91's as he stated to me. It was a "disaster."

I can definitely understand why, considering what I experienced with my 93 and the smaller 24mm rear bar.

Please keep in mind, we are talking 10/10th's driving here, ***** to the wall. Not simply a spirited ride down a back country road. What works on a street car with a factory alignment may not work very well when sticky tires and aggressive alignments are thrown into the mix. Again citing my own experience.

Believe me I'd like to pick the brains of the engineers to figure out what they where trying to accomplish and why they did what they did. I have a good idea, but I cannot prove it beyond speculation.

IDK, gotta go with what works.

 

Rubie, you are the best, thank you so much!

Sounds like the Z07 setup is the way to go. And the best part is, it keeps you in stock class! I was wondering how much of a step up the Z07 was from FE1, but from your experience it seems to be a huge difference.

I've heard from others as well that the 26mm bar is too large for the rear. For spirited driving on backroads it must feel great, but during *****-to-the-walls autocross the back end must get really snappy, which is obviously not good. I love the way my C4 handles now, it's very neutral, but the response is not there but the body roll is.

My only concern is the availability of Z07 parts. I've heard its tough to find the springs and especially the sway bars. Would it be feasible to try a 32mm hollow up front and 26 hollow in the rear?

 

Don't have too much experience with them yet but I just upgraded to the z07 springs fhb and nyu, 32/24. I have a non functioning fx3 I'm trying to figure out. I'm more of a road course guy but as for the roll, it fixed everything. The shocks ar my problem now. I run them in continentals too so more grip than your nittos. I did have the same response about the 26 vs 24 and the more research and response I go matched.

 

The rear spring is fairly easy to find. The front spring and bar are a bit harder. Get a hold of CorvetteNutz on here, he is a vendor. I got my stuff of him, not cheap but I felt was a fair price considering its getting harder to find the stuff. Don't let mileage scare you on fiberglass springs. My Z07 stuff has 236K on it. Fiberglass leaf springs don't really wear out from use. Only chemical or physical damage can hurt them. GM wore out their testing equipment before they hurt the springs!!!

The 32mm/26mm hollow bars should work. That is basically a 30mm solid/24mm solid. Use rubber mounting bushings. As I noted in a earlier post, you can use them to adjust the car some. It really does work.

What rule set are you operating under? How strict is your region/group?
How close do you want to stick to the rules?

I'm actually (when I get time) trying to compile a comprehensive summary on C4 setup for auto-x and such. Hopefully, it can be a sticky once I'm done with it. These cars are old, so no real secrets anymore.

 

Here is a pic from a auto-x this year. Not the best one, but you'll get the idea. Z07 springs/bars. ZII 255/40/17's at all fours.

This is a typical 180 sweeper-medium speed. The fast guys where hauling *** thru this, I was one of them. Car is NOT under braking its just turning in this pic. My line wasn't the best for this pic, but.....

The point is, very little body roll. A little but not excessive at all. My Avatar pic=FE1 stuff, yeah, its soft.

 

This is a sweeper at about 65mph with a 32-26 setup. If you lose your tail it's your fault not the cars. Your either going in too hot or not counter steering. Notice how little roll there is.

 

Not much body roll at all! I need that stuff!

Kimmer, you have almost no roll at all in this pic. You must be running 32-26, both solid? What do you have for springs?


Thank you so much for the help, this will determine my winter modifications!

 

Yes both are solid, I put in the NYU in back and the FE1 is in front I believe. I never took it out so not sure but since the rear was stock a I'm sure the front is to.

 

If your rule set is pretty open....

Good Lord! You could do quite a bit to make a C4 better and keep it reasonably street-able.

The 32mm solid/26mm solid combo would work b/c of the stiffer front bar.
It works for Kimmer, so that is an option.

I would just never pair the 30mm solid with the 26mm solid and have the stiffer springs.

Yeah, the longtubes would bump you to BSP in SCCA. You could do a TON of stuff in that rule set.

 

So you're running the stiffer rear spring but kept the FE1 front spring? I'm curious, why did you not put the stiffer spring in the front as well?

You seem very excited for me!

I agree that the 30 and 26 solid will not work, didn't they do that on the '91 Z07 and it handled poorly?

How do you feel about 32 and 26 solid on FE1 springs? That would still be streetable I assume (I live in New England so the roads suck here, I'm used to bumps), but would it be alright to use such large bars on FE1 springs?

 

The 91 Z07' from what I've been told and MY own experience backs this up, handled well to a point at which you got snap oversteer. Just too much rear roll stiffness.

I think the 32/26 on FE1 springs would be ok. You won't have the roll stiffness of the Z07 springs+the bars so you'll be ok.

The stiffer springs help in auto-x more so than road racing with all the transitions. SHOCKS are huge for this however.