thurman_merman

I've been reading a lot of old threads on upgrading c4 suspension and a few have mentioned keeping the soft springs and adding big sway bars but I haven't found anyone who actually runs it on a c4.

I have a factory 91 FE1 (93.1/39.9) (26t/24s). I have considered adding a 30s front bar and 57.2 rear spring to mimic the Z07 setup but honestly, I would like to keep my soft ride. I drive at a local racetrack and it's really bumpy (H2R); I also drive on crappy back roads.

My question, is anyone actually running a soft spring setup on their car. I would love some insight without having to swap bars all day long in the Texas heat, not to mention the cost of buying all of these bars. Or should I bite the bullet and get the stiffer rear spring? I'm not looking to get beat up all day so the 115.5 spring is off the table.

My setup: 93.1/39.9 springs, 26t/24s sway bars, poly bushings all around, Bilstien Z51 shocks, 18x10.5/295 wheels/tires. Street tires for now, probably nothing stickier than R888 for a while.

Thanks for the help.

Solofast

While the Z07 package is stiff, you'll find that shocks have a bigger impact on ride quality than springs. If you get a set of adjustable Koni sports you can soften them quickly and easily at the track and have a liveable ride quality on the street.

I ran the Corvette Challenge shocks on the street for a while and they were brutal. The Bilstein shocks are fine, but they're a bit harsh for the street.

Going full soft on the street and then turning them up about half way on the track gives you the best of both worlds.

thurman_merman

Thanks for the reply.

Are you saying I should use the Koni sports with my current setup or with the Z07 rear spring? My straight line is fine as far as ride quality and soaking up the bumps on track, my problem is all of the body roll when cornering. Not that it couldn't be much better with a good set of shocks, I do like the idea of adjustable shocks.

froggy47

When I had my lt4 (1996) I had base springs & put some big bars on, I don't recall the size/numbers on the bars. It was pretty good. It's called a European suspension set up.

I also had Koni single adjustable & disliked them. The adjusters get stuck in full (hard or soft) settings and the lower bushings (front) pop out (unless Koni has fixed all that).

thurman_merman

96 springs are crazy soft. Did you feel the car was pretty neutral with the larger bars of did you have to fight it through the corners?

Thanks for the input.

thurman_merman

If I could boil down my question I guess it would be this: would it be worth it to try a 32(or 30)/26 sway setup or is it just not enough with the soft springs to flatten it out in the corners? I would like the car to remain neutral and I could do a little tuning with bushing material and alignment shims to help achieve balance. Has anyone had this setup on a road course and kept it or changed it for any reason?

froggy47

It still pushed some, but that was more the alignment than the bars. Eventually I put stiffer springs in also, I Hillary the spring rates (I don't recall).

My c5z (with stiffer springs and bigger bars than original c5z) is now on rails & still ok for short local street drive.

thurman_merman

I'm on the fence. Ill probably end up trying both unless someone chimes in saying the bars on soft springs is a waste of time. I did read somewhere that some believe there just isn't enough sway bar out there to keep soft springs planted on the c4. Somehow I need to find out.

froggy47

You may recall when the c4 came out (1984?) the car had wicked stiff strings, complaints from the guys who drove the car to the golf course on weekends abounded. The So Cal freeway concrete strip separations, especially, brought out the worst.

GM went all over the place with c4 springs (who was running that dept. at the time?).

Yes, the 1996 base had especially soft springs (mine) which needed replacing for comp. use.

Kubs

The Z51/Z07 springs on a C4 are what I consider soft. They are only around 600lb front and 330lb rear. I have the "stiff" springs front and rear on my race car with a 32mm/26mm sway bar combo. It works really well. Other racers I know have 1000+lb front springs and almost 400lb rear springs. To me thats too much.

thurman_merman

What spring rates do you run on your car with the 32/26 bars? Track only car?

radar502

I asked the same years back when I had C4s how to make it handle ? lots phone calls and even more emails ,this is what I took from away from the info I got from old time C-4 racers . Can't make the front suspicion too stiff and the rear has to be able to keep the car from rolling over too far but not too stiff and the rear tires have to be in contact with the track ,if too stiff you will kill the independent rear and will not work right ,so I put a big bar in the front really stiff shocks but with some movement little moment got to have some . The rear I think 28MM bar been a few years back , rubber bushings not poly too stiff will not let the bar do it job medium stiff shocks also ,got to find a happy medium in the rear has to be able to move good tires .The alignment has to be right for a C-4 to turn ,I did between a auto cross and progress street aliment worked good . Brakes have to have very good brakes also , why you can push a C-4 just so fair bam hit the brakes reset the thing and gas and go ,it helps to know how to drive also .. Stiff front movement in the rear good brakes good tires get your driving down won't be a full time track ride but will be suppressed on how good it handles . I shocked a lot of people in my 96 LT-4 had lots of C-6 Z drivers shocked to see me on there bumper could not pass didn't have the power the look on the faces priceless.. That 96 Lt-4 was nice ride ..

Kubs

I am using the factory 1990 Z51 spring rates. 115.5 F and 57.2 R (FHA and NYU codes I think). Keep in mind I have also taken a lot of weight out of the car making the effective rate of the spring higher. A full weight street car has more weight available to compress the spring.

My sig shows the car going through a slalom at an autocross with minimal body roll.

rfn026

I had the very same question a few years back. I went to The Master - Danny Kellermeyer.



I'm a soft springs and big bar guy. Danny told me to put the Corvette Challenge springs under my car. He said the problem was that while my idea was correct the problem was that no made big enough bars for the C4 Corvette. This meant that I had to stiffen the springs. It worked.

Bilstein built my shocks for me. Danny said that means I have too much rebound. Bilstein loves huge rebound numbers. Danny - no so much.

I also added the Kellermeyer adjustable rear sway bar. The trick with that is knowing how t o set it. You have to determine what your car is doing in the middle of the corner. According to Danny "All Corvette understeer on entry. All Corvettes oversteer on exit. What is the car doing mid-corner."



Danny also does front bars. Some people feel it's easier to adjust the front bar at the track.



Richard Newton

TurbineSurgine

I think the only way you are going to find out what works for you is trial and error. What is considered a harsh ride to some isn't to bad for others. Also it all depends on how your car behaves and how you want to tune the suspension, do you have too much oversteer or understeer. I know for sure the poly bushings in the rear add harshness because they bind the suspension. I swapped to banski rods and the rear softened up and allowed the proper articulation, i think it was the best suspension mod i have done. Also banski emailed me the other day that they are having a sale. I think z51 or zo7 springs and bars are just right for track and street, the base springs where meant to please the corvette buyer that really wasn't into spirited driving and just stood around in their corvette jacket drinking out of their corvette mug on saturday mornings. If you are going to run r888's you are definitely going to need higher spring rates and stiffer bars. Below is my car and how much roll i have on 84 z51 springs, 32mm front bar and base 85 rear bar. The stiffest springs i can get and biggest front bar i can get, I left the stock rear bar because i had pretty bad oversteer. At that time i had ridetech hq shocks but have since switched to c4 challenge bilstiens that are stiff on compression. thats my opinion, some may agree and some may not

thurman_merman

Thanks for the replies and advice everyone. I think I you guys have told me what I needed to hear about how soft my factory suspension really is. I'll start with the stiffer rear spring and tune from there. I feel like I'm pointed in a much better direction now. Thank you.

I had no idea about the binding rear suspension with poly bushings. I have done some searching and reading up on it and I'll definitely get that sorted out sooner rather than later.

Richard, are the kellermeyer bars custom units or are they corvette bars that have been modified with adjustable ends? What size bars do you run with your challenge springs and custom shocks?

I have more research to do but I'm leaning toward a new rear spring, large bars, and adjustable shocks like the Konis sports or qa1 to try and get the suspension dialed in. Does that sound like a good place to start? I will also look into banski pieces and other aftermarket suspension geometry improvements but it seems that there is a ton of stuff out there from adjustable components to DRM brackets that move mounting points and I haven't dug that deep yet.

Kubs

I believe Danny K just modifies the Corvette bar to have the 3 hole positions.

I will also agree that the Banski kit really made a huge difference in both ride and handling on the car! It is a MUST!

I would not go too crazy all at once. You need to see what works and what doesn't. Making 12 changes at a time would not give you any real input on what helped and what didn't. I think you could do springs and bars at once and see how it feels. Next shocks, and get them dialed in to match the spring/bar combo. I currently do not have any geometry altering brackets on my car as I didn't feel they were necessary.

TurbineSurgine

I agree with this, I have the drm trailing arm bracket, tried it and didn't experience any kind of change, pulled them off and they sit on the shelf. The concept is supposed to be that it reduces anti squat, thing is the rear knuckle does not connect to the center diff like a solid axle would, so the torque does not transfer to control rods, only during braking. The camber rod brackets reduce camber gain with travel, I wouldn't think you would want that unless you drag race. If the car rolls when you corner you would want some camber gain (negative camber) to keep wheel from going into positive camber. If your on a budget I would check ebay for a used z51 spring, the bars are cheap enough new. Bilstein shocks are good value, I use the challenge valved shocks but I think other venders like drm, vbp, have some with their custom valving, all are around a 100 bucks a corner. It's really not that expensive to setup a good track suspension for a c4, you could also make it as expensive as you want, just look at penski shocks. As far as the banski stuff goes I went with the dog bones and camber rods, I figured the tie rods where on ball joints so there is no binding there. I'll probably go back later and pick some up to complete a full set.

HandsomeMike

Thurman, I have the same setup you're talking about. 93 front, Z51/Z07 57 rear. 32/24 bars. Bilstein sport (Z51) shocks. The 1992 Z07 was 90/57 springs with 30/24 bars and Bilstein sports. So the 93 front spring is a touch stiffer and the 32 bar a touch bigger. I used to understeer with base springs and 32/24 bars and sport shocks and then added the Z51 rear spring and everything became neutral. My first test with the 93/57 springs, 32/24 bars and sport shocks was a few weeks ago at the NCM Motorsports Park and the car was completely neutral balance. I loved it.

thurman_merman

I misspoke eariler when I said bilstein hd shocks, I have the Z51 shocks.


Kubs, that's what I'll do. I'll change the spring/bars first, banski stuff after that, shocks after that. Then I'll dive into the advanced stuff after that if I feel like I need to.

I'm not going to call it a budget build but I'm not going to put a lot of money into this car either. I know there are better platforms to start from if I want to get serious. I will get those trailing arm bushings handled asap though.

Mike, thanks for chiming in with your setup. Since my factory rear bar is 24mm I'll stick with it and just source a NYU rear spring and a 32mm front bar. That sounds like a good place to start.

I'll be referencing this thread for the coming months as I try and tighten this thing up, if you have anymore advice I'm all ears.

Thanks again for the help.