blackozvet

The c4 z51/z07 springs and swaybar combos are so well engineered for the cars that they really are the starting point.

I agree with solofast, the shocks are the way to tune the performance and ride of the car.

If you use adjustable shocks you can easily vary the ride between comfort and performance on the road or track, that would be the best area to start experimenting with.

Solofast

The QA-1 shocks are an unknown. They mostly do drag shocks so I don't think that's a good idea for what you want to do. The Koni's work and work well, and set to full soft are very liveable on the street.

The issue with rear bar poly bushings isn't that they bind, it's that if you have too much rear roll stiffness the rear will jack due to the high rear roll center. The combination of bar and spring is the issue, if you have a softer rear spring you can go to a bigger rear bar (as they did with the ZR-1 setup) or if you go with a stiffer rear spring you have to soften the rear bar. Big rear bar plus big rear spring equals jacking and oversteer.

The Z07 package is about as stiff as you can comfortably go on the street. It's a bit firm, but with soft shocks you can live with it. Add stiff shocks (like the Corvette Challenge Bilsteins) and you have a kidney crusher of the first order. I had that setup on my 1990 car and it beat me and the car to death. After about 7,000 miles things were falling off the car (the rear hatch switch in the door fell apart and it started opening at speed) and the trim was cracking and rattling. I'd drive the car to an event on the stock shocks and then change to the Challenge shocks and change them back before I drove home because it was so punishing to try to drive a long distance on those shocks.

69autoXr

That is a damn fine looking front bar setup.

HandsomeMike

Question... And I don't mean to hijack the thread but it may be good info for the OP too. Is body roll control all in the springs and bars or do shocks play a roll too. I know shocks control the rate at which the springs compress and rebound. Just curious.

blackozvet

Geez Mike, people write whole books on this subject !

springs control the weight at each corner of the car, and subsequently control the movement of the wheels on the road surface,

shocks control how quickly or slowly the springs reacts, a stiff shock will overdampen, a soft shock will under-dampen.

anti roll (or anti sway) bars are called that for a reason, they are extra spring rate that is introduced during cornering to HELP control body roll, and therefore weight transfer during cornering.

so they all play a part, if we get any more technical than that we will start writing a book

HandsomeMike

LOL!!! Thanks! Was thinking out loud. I could talk about this all day.

93Rubie

For the record I find the 93 Z07 with Koni Shocks to be very very good when combined with a few sway bar, rear spring setting, and alignment tweaks. All with STOCK components other than the shocks.

pkincy

My 93 has coil overs so can't help there, but my 94 Z07 was stock and adding Koni's to it also was a winning ticket, leaving the rest of the suspension stock and running Hoosiers or Koni's depending on the year.

BTW, the best add I did was putting the convertible X brace on the 94 coupe. Without it I could jack up one wheel and the other on that side would still sit on the ground. With my Z06, I jack up one point and the whole side of the car comes up evenly.

blackozvet

Yes, when you track your car suspension becomes more important because you get timed, so you soon find out what works and what doesnt !

A lot of people ponder the ideal spring rate for their c4, but the reality is that the GM engineers have already done the work for you. Spring rate is a mathematical equation based on a number of inputs. If you look at the Z51/Z07 spring rates it gives you the answer.

Sway bar rates are a bit more educated guess and trial and error. Again the GM engineers have spent millions of dollars (when you factor in the catering bill) and worked it out.

https://www.corvetteforum.com/forums...84-96-z51.html

the spring rates went up in '88, partly due to the a slight increase in wheel track (from memory i think it was 1") and I suspect a desire for some extra spring rate.

So that leaves shockers as the wild card, and the reality is that only a small number of humans on this planet have a real understanding of how they work and how to tune them. Its a matter of 'you get what you pay for'
You either buy reputable brand shocks or buy adjustable and learn how to adjust them.

Solofast

The Koni Sports for the C4 were tuned by Dean Dodge.. He is one of those few who really know... He brought 3 sets of shocks to try on the later C4's.. I did the driving and Dean rode and tuned and it took more than a day of testing, but the ones that got to production were the best of those and are still a great shock for that car today...

To be honest all of the shocks he brought were good, but he had the background of testing previously on Roger Johnson's car and knowing the spring rate and geometry changes from the early to the later C4's, we were just dialing them in a bit, the hard work was already done.. By the end of the second day he had it all down and that's the shock that folks have used on that car for the last 25 years...

TurbineSurgine

If he did the shocks for Roger Johnson's car then why aren't any konis available for the early c4?

blackozvet

and I guess that is the reason why Koni enjoys the reputation as a 'go to' shock for the c4.

I spoke to one of the guys from Supashock (they supplied the coil-overs to the v8 supercar championship winning team) who are based here in South Australia, most of what he said went over my head but the thing I do remember is that it costs a minimum of $300 per shocker to dyno and rebuild (after you give them all the numbers on your car). Not bad for a shocker that cost $250 each new !

Solofast

Roger had the "Red" Koni's on his car, I didn't give it a thought at the time, but as we were doing the testing and and Dean was talking he mentioned that he used the valving he had developed for Roger as a starting point for the valving I tested...

In 20/20 hindsight I'd bet that his shocks didn't have the same valving as the normal Koni Red shock that you can buy...

Remember that when the C4 first came out it was classed in A/S against the Loti and it wasn't considered competitive. Nobody was running them and frankly there wasn't any demand for a sport shock for the car at the time. Roger went to the C4 in 86 when the car was reclassed into B/S and finally won with it in 1988. By then the front suspension had already been changed and I don't think that Koni was really seeing much demand for an autocross shock for the car that wasn't being run by that many folks. Dean approached me in early 1989 to do the development of the sports but I don't think that they felt it was worth it to go back and make a sport shock for a suspension that they only made for a few years.

EDIT

I thinking about this last nite after I posted, a comment that Dean made stuck in my head. I was thinking that Koni made tons of shocks for autocross in those days.. Dean replied that no, the real money was in drag shocks. He said (at that time in 1989) that maybe they'd sell 20 or at most 30 sets of Corvette autocross shocks in a year, if they had a good nationals with a sponsored car in a non-pro class at the drags they'd sell over 100 sets of shocks in short order, there were just that many more folks doing drag racing and that if the word got out that their shocks really worked they'd sell bunches of them, where with autocrossers, it was a much lower number, just not that much money in autocrossing.

Nokones

The 1993 ZO7 package had the stiffest factory springs put on a C4 and was the best autocross suspension package offered for a Corvette. The Bilsteins are junk and the ride is very harsh. I put a set of Koni Yellows single adjustable on my 93 Ruby when I was autocrossing it in the stock class.

On my 1989 C4 that I compete in the SCCA CAM program, I am running a 1420 pound spring in the front and 840 in the rear with Penske's Triple Adjustable shocks with external reservoirs. I don't use a rear swaybar. MY front bar is a custom adjustable with remote control. I am running the BFG Rival S 315s on the front and the 335s on the rear with Forgeline 18X11 & 18X12 1/2 respectively. I am able to corner balance and adjust the ride heights with these springs. This is very important if you want a good handling car.

I tried the 1240 pound spring in the front and a 730 in the rear and the would noseover in the turns like you see the black C4 doing in the picture in the above posting. Now, the car stays nice and flat in the turns and I really didn't have a problem running this setup in the rain at the SCCA Solo Nationals & CAM Invitational. I was kinda surprised that it did work in the wet. I expected the car would be ill handling in the wet and I was surprised.

Note: Dean Dodge knows his stuff when it comes to autocrossing suspension and what shock to run. He was one of the very few who knew anything about autocrossing back in those days. Did you know that he once worked for Dick Guldstrand back in the day. I had some Dean Dodge stuff on my 1990 Camaro 1LE and what a difference it made and that is why I was able to when championships at the SCCA Nationals.

rfn026

Shocks are the last piece of the puzzle. Koni engineers believe you have to get the spring/bar package together first. The shocks are then used as a final tuning device.

You should probably do both springs at one time. A stiff spring in the rear and a soft one in the front is not ideal.

I have a 30mm bar in the front and a 26mm in the rear. They're both solid bars.

One thing you might check is your front bar. Water gets into the mounting brackets and corrosion builds up. At some point the bar does not move smoothly.

Remove the bracelets from both ends and try to rotate your front sway bar. You should be able to do this easily with one hand. If you can't you'll have to remove the bar and clean the corrosion. Then use silicone lube when you put it back together.

Richard Newton

Solofast

On C4's if you're using the stock rubber sway bar bushings and bars they aren't designed to be "free" or side in the mounts, they clamp the bar tightly and the rubber deflects as the bar twists. This has advantages in that the rubber doesn't wear, it only flexes as the bar twists. The bad part is that as the rubber ages the spring rate of the bar changes because the stiff rubber bushing is part of the sway bar (and wheel spring) rate and as it ages it gets softer. Putting in bushings that allow the bar to slip in the mounts is fine, but realize that you'll need a stiffer bar to get the same rate with that kind of setup. The reason is that the tightly clamped bushing adds a significant amount of stiffness to the bar so if you put in poly bushings you think that this will make the overall system stiffer, but you don't gain as much as you think you will gain because now the bar slips and twists more easily, where before the bushing resisted some of that motion.

The other advantage of tightly clamping the bars is that they don't "walk" to one side or the other or need some kind of clamp on the bar to keep them from moving across the chassis. The clamping thing works, as does a "slipper" bar, it's just a bit different, but the OE bars and rubber in a C4 aren't supposed to be free or easy to move when not attached to the suspension.

HandsomeMike

If you want to see what my setup looks like in action, watch this onboard video from a C7 that was in my group during a HPDI (introduction) last month at NCM. 93/57 springs (FE1/Z51 lowered), 32/24 bars, Bilstein sport shocks. Continental Extreme DW tires. . The Porsche Boxster was our instructor and the voice on our radios that you hear. We're doing passing drills.

Nokones

If my memory serves me right there were two concepts of suspension setups for the Corvettes. The soft spring and big bars was the Herb Adams concept and the stiff springs and small bars was the Guldstrand concept. For many drivers both concepts were fast and it depended on your driving style and of course, the shock setup.

69autoXr

The information I've seen is that the '88-90 Z51 and '91 Z07 had the stiffest front springs of the C4's at 115.5 N/m, one of the reasons in particular that I keep my eyes open for a '91 Z07. '93 Z07 is shown as 90 N/m. Are you saying this is not true?

Nokones

Sorta - I stand corrected on the 91 ZO7 front spring rate. The rear spring rates for the 89, 90, 91, & 93 is the same at 330 pounds. The 89-90 front spring rate is 628 pounds and the 91 is at 885 pounds where as the 93 is at 795 pounds. I have had this discussion a gazillion times before and I should have known that but, for some reason I thought the 93 was the stiffest. It may have been from a previous discussion on what would be the best C4 to autocross in stock trim that was still stuck in my mind. Sorry for being sorta wrong.

In my opinion, in stock trim the 93 would be the best C4 because of the LT1 with the horsepower and the better LT1 CAM profile/torque and the ZO7 suspension package and I have proven that running against the 89s and 90s many years ago. The 92 LT1 cam sucked for autocrossing. Although, the 93 C4 was 100 pounds heavier, it was very difficult for the 89s & 90s to beat me in my 93 C4 Ruby on both tight and open courses those drivers were no slouches. In fact they really never did beat me once I got the car dialed in.

I remember that I would have them beat on my first or second run out of 5 runs at each event. They even tried to design the courses to their liking and I would still come out on top. Those were the fun days back in the mid 90s.

And yes, I still have my Ruby. It is a grocery getter now.