rithsleeper

So usually I race an rx7 with scca but have my 1989 c4 I run with nasa hpde. I am going to start instructing and so I will be getting some free track time along with taking students and friends out. I want to be safe first along with being able to use the car. Stock suspension doesn't feel safe...

I just got back from road atlanta and wow that was fun. If was my fist time dealing with elevation change (I frequent roebline, cmp and occasionally cms). However as stiff as my suspension is on the street if felt like an explorer on the track. It has tons of body roll and gets so loose over gators. I have a mildly modded l98 so I have plenty of power and running continental slicks, by the end of the weekend I was turning 1:48 lap times.

I feel like there is so much more to the car and I finally have brakes ok with c5 upgrade and ducting. I feel I could eliminate a second alone in the esses. And don't get me started on turn 12....

Thing is funding is an issue but I have enough not to skimp. First, I drive the car maybe 300 miles off track each year. So comfort isn't an issue but this is not a race car. Before the next event I will have a roll bar in the rear. I have plans in the near future for a new engine. I have the money but I feel suspension is priority. I also have creaking bushings so those will be new soon also.

I can do everything myself if needed but the more money I save, the sooner I can get my engine or a million other things needed. I don't want to spend over 1000 if possible and would not be looking to get something new because used is just as good epecially if its only used 4 track weekends a year.

Any ideas? Or anyone have any parts they are looking to sell? Coil overs? Stiffer leaf springs? What spring rates should I look for?

Crepitus

Are you starting with FE1 or Z51? This has the potential to be an extremely interesting thread because I have a 84 Z51 spread all over the shop that I want to do the same stuff with. There are at least a half dozen very knowledgeable guys on this board that I would like to hear from. Hope you dont mind if I ride your coat tails here

rithsleeper

I have the adjustable suspension but it doesn't respond to commands (fx3 system). But this is a shock problem, that would effect more when I hit a gator, not body role.... I'm know there are a lot of c5 guys but hopefully some c4s will chime in.

I know coil overs might actually be overkill... its not like I'm corner weighting... and I don't want to have a different spring set for each track....

kimmer

Put on bigger sway bars, 32mm front & 26mm rear. It took care of my body roll problem.

BrianCunningham

how old are your shocks?

rithsleeper

I don't know about the shocks. I've owned the car for almost 4 years now . Never had to worry about the shocks, the car doesn't bounce alot on the road or anything, its just on the track it feels like a caddilac (very comfortable, just not performance.) The car has 146K on it but I don't think they are original. The stickers are still there and they are still pretty yellow. looks like about 30K of grime.

I agree with the sway bars, would that be all I need? would that completely fix my body roll problem and then move to a stiffer shock so it doesn't have as much travel?

Where did you buy a 32mm front sway? I can only find 30mm...

Also what did the Z51 package come with from factory as far as sway bars are concerned. I found another post saying that when combined with the fx3 they downgraded the sway bars to base model!!! LAME. I got under and measured and sure enough, 26mm front/22mm Rear. I think that might be my problem!

I still am interested if anyone thinks I need to do more or where is best place to buy sway bars.

lbs90ZR

I put Lingenfelters FX3 chip/controller for road course, it made a noticeable improvement by keeping the shocks near full absorb all the tme.

But if I read your post right, yours doesn't respond to FX3 selections. If it needs repairs, it might be cheaper to get non-FX3 shocks and forget the FX3.

I put 32S and 26S from VBP, stock was 26T and 24S. It seems to have no body roll on the street, but hard to really get a feel of it on the street. I have to wait 2 weeks for the track. I also put their Smart Struts on the back, they're great for adjusting camber.

Bought their stiffer Extreme springs also, but just got the rear one and didn't have time to install them, so going with stock front and rear spring.

lbs90ZR

There is a online c4 suspension tuning chart, if it is right. It lists 89 FX3 also has lower spring rates front and back 93/39 with the sway bars you listed. Z51 has higher spring rates 115/57 and the bigger sway bars 30S/24S.

rithsleeper

Ill have to varify spring rates but I did read that z51 means a 30mm/26mm sway unless combined with fx3, it is a 26/22... would be interested to know. What is the link to that list of suspension info. Would be good to know what year/options to look for on part outs.

Solofast

Here is the C4 suspension chart. With an 89 you don't want to go bigger in the rear than a 24 mm bar. Couple that with a 30 mm front bar and the Z07 or Z51 springs and you will have a pretty stiff extremely well balanced setup.

http://www.corvetteforum.net/c4/gcro...sion_chart.pdf

Add a set of Koni sports and you will be about as good as a C4 can get without making it kidney belt stiff.

1991Z07

Other than the Corvette Challenge cars, the Z07's have the best track manners for factory cars.

Rippie sells an FX3 coil over setup for the C4 as well.

I'd also make sure the suspension bushings are up to snuff...

shakedown067

With my base suspension car, I just went full monte with double adjustable coil-overs from Van Steel! I'm loving the ease of adjustability and the ease of swapping to even stiffer springs as I grow into racing slicks and the car becoming more and more of a track only car. One day I know she will only see the highway from a top of a trailer. So I went with my long term goals, and coil-overs made the best sense for me. I also NEVER wanted to have to deal with that front leaf spring again. What a PITA. Good luck!

Solofast

No question about that. You can dink with setup for a long time and still have a tough time beating a Z07 with a good set of shocks.

Very good point. You are talking about a 20 year old car and the suspension bushings are pretty much toast by now.

Were I tracking a later year C4 I'd go with a Z07 package of springs and bars, add a set of Koni's, and put in a set of offset lower control arm bushings to get some more negative camber. After that, drive it like you stole it...

Crepitus

I agree all the maintenance stuff needs to be done first. Bushings, ball joints, wheel bearings ect ect. The go fast stuff is great but if there is a soso ball joint or something under there that could last another 10,000 on a daily driver it will probly lay an egg on you and maby leave you in a smoking pile of junk. Any thing that is loose and pointing in the wrong direction now and then will pretty much make it impossible to get a read on what the setup needs. Thats why mine is in the back bay on 4 jack stands. I really dont know how the stock setup handles because there is so much sloppy stuff under there.

1991Z07

Mine is due for a refresh this year...it's been nearly 40k miles since the suspension was completely rebuilt. It's had a few track miles, autocrosses and road miles on it...so there IS some sloppiness in mine.

I will have the rear end out of the car this month to fix a leaking axle seal...gonna be a great time to pull the Heims off the back and replace them. I already replaced all the wheel bearings about 1000 miles ago...so after the rear is done just front bushings and I'm back in business.

Something I noticed when I did my suspension the first time...I got the FX3 Bilsteins rebuilt to Rippie specs and their FX3 controller. This picture was taken shortly after I refreshed the suspension...



This is what a Z07 suspension looks like when it is working. Flat through the corners...

If you have no idea what the condition of the suspension is like...start from the ground up and refresh it. Replace the springs with Z51's, put new sway bars in, put urethane bushings in, new shocks...it'll be like a different car.

Crepitus

Nice pic! headed out to the shop right now.

rithsleeper

Bearings are good, ball joints are new, bushings prob need redone and planned on it when upgrading the sways and new rack. I have the z51 spring, do they ever wear out?

Van Steel

Bigger bars are not always the solution, especially in the rear. Depending on your tire compound, the car may need to roll more.

Solofast

Make sure you are keeping things balanced. You said you had a Z51 spring... If you change one spring you need to change the other. As Van mentioned, be careful what you do with springs and bars. You can go too far with the rear bar and make the car undriveable. Use the suspension chart as a guide and then look at bar and spring rates and try to keep things proportional.

If you aren't using a "package" of springs and bars that came on the car as an option, or are a kit package from a reliable supplier and tuner, then you for sure want some ability to adjust and tune the setup or you can easily end up with something that pushes like a pig or you end up looking out one of the side windows at where you are going. Neither is fun, but on the track it can get really exciting or expensive.

Plenty of folks here have already been down this road, if you post what you intend to do there are folks here that have, most likely tried it, and can keep you from doing anything stupid.

93Rubie

Even with my old worn bushings and stock FX3 shocks, the Z07 springs and bars on my 93 made a WORLD of difference in the way the car handles. Solofast seems to know his stuff, I've setup my car per his recommendations. I set FTD on STREET TIRES on Sunday at our clubs auto-x event. Enough said.

FYI, the Dunlap Dizerra ZII's work AWSOME!!!! in 255/40/17 at all fours. They work in the wet,cold,cool,hot,dry, doesn't matter. Wear is excellent considering I'm camber limited....for now. I have close to 90 runs+some street miles to and from events. I WILL need to flip soon, but tread in center of tire is about 6/32. New they where 9/32 or so.

Pretty much anyone who has driven my car has nothing but good things to say about it.