Green Smoke

Since C4's have been around for a long time, there should be no secrets about what is the best autocross setup. I have a '94 base, 6 speed, with the FHA 93.1 (532lb) front spring and the NYR 39.9 (228lb) rear spring. The front and rear sway bars are both about 24mm. This will be a solo only, BSP car with 274-17's all around. What do you recommend as a good foundation of matched springs, bars and shocks?

Solofast

What is limiting on the C4 in BSP trim is the total rear roll stiffness. Too much and the back end will jack. What this means is that at some point the combined rear spring stiffness and sway bar stiffness gets too high and you will have problems.

Lowering some will help, but the car can't be lowered a lot without getting on the bump stops and if you do everything will go to hell in a handbasket.

Take a look at Hib Halversons C4 suspension chart

http://www.idavette.net/hib/c4/sustunch.pdf

you will see that with softer springs they have gone with stiffer rear bars, but with the higher spring rates they stayed with the 24mm rear bar (or even 23mm rear bar in 84). In stock trim the 84 jacked a bit on street tires and could be a handful on sticky tires at stock ride height. The 91 Z07 cars jacked with the stock setup, the 57.2nm springs and a 26mm rear bar, and they only did that combination for one year and it was a disaster. We used the 84 Z51 rear sping with a 24mm rear bar, the car was lowered, and it jacked in the rear. We took out the poly bushings and put in rubber and it still jacked some. We softened the rear swaybar bushings to get it under control. Since you can't really change the geometry in BSP you are pretty much limited as to how much you can stiffen it up before you get into trouble.

I would get a set of rear Z07 springs (57.2nm) and stick with the 24mm bar in the back, and maybe use a set of poly bushings back there.

In the front we went with an 84 Z51 front spring since we had the older front suspension. With your later model zero scrub suspension, you probably want something like the 91 115nm front spring and then tune with the front bar to taste. You can't go crazy on the front spring stiffnes since that would overpower the limited rear oveall roll stiffness, so that pretty much sets the stage. For a front bar you want at least a 30mm solid bar or bigger...

For shocks I would look at Koni sports since they were tuned for the 115nm front spring. If you go higher in front spring rate, you will want more damping than comes with the Koni's. The rear Koni's you will run pretty soft, but at times the fronts will be on full stiff.

Solofast

As an aside, according to Hib's chart your base coupe front spring rate was 73.2 and not the 93.1 that you were quoting. The 93.1 is the base spring for a 1991 coupe. By 94 the front spring rates had gone to mush and this is primarily why the last of the C4's were seldom used in super stock since there was no way to make them competitive with the earlier cars that had a lot stiffer springs. If you have a 94 with FHA/NYR springs, somebody changed them out already.

Here is a link to the spring codes for each year.

http://www.corvette-guru.com/modules...?post_id=98314

Scroll down to near the bottom of the page

Green Smoke

Thanks much. That is exactly the kind of information I was looking for. I did spend time looking at Hib's chart trying to match spring rates, tire sizes and sway bars. I was surprised to find the heavier springs on my car, and also the similar sized sway bars. I haven't pushed the car yet as I am still squirming around underneath to make sure everything is there and well attached. I haven't been around Vettes in about 15 years, so it's taking awhile for it all to come back.
Thanks again for taking the time for you detailed reply.