93Rubie

For better or for worse, I ran my first ever event in mid August, I just did my 4th one last Saturday. It is a ton of fun, and I am learning a LOT, both about the car and me. Kinda of funny but the more I use my Corvette in motorsports and drive it too, the more I really love this car. It proves itself over and over again as being one of the best sports cars in the world. If not THE best. FYI, I think I held my own in B-stock against folks with MUCH more experience in their S2000's and Boxsters. We all where in the tire class=street tires so that evened things up a bit. The course was fast and open. Something my first 3 times at auto-x the courses where extremely tight by comparison. My best was 43.8. The others best in the low 40.XXX bracket. I did beat a fellow rookie in his 08-present Subaru WRX STI.

Nice to see a 18 year old sports car kicking new machinery to the curb. I can tell looking back where I lost speed and what I did wrong. The car has SO much more speed in it. Needs a better driver... Less hamfisted inputs and throttle applications... and more smooth. I was lower mid-pack with my PAX times. Closer to mid-pack than the bottom.

To get to the point of my post, I have been studying the SCCA rule book for Stock classes, C4's are in B-Stock. It allows some room for mods but very little. I intend to stick to B-Stock because...A: It will take quite a while before I get to where I can outperform the car. Even a C4 has very high limits and performance potential. B: It is cheaper... C: Since I drive, show, race, etc...this car closer to stock the easier to maintain and live with.

That being said, my 93 has the FX3 suspension, I can run the Z07 setup as it was an option on my car. Since mine does not have Z07 I will have to piece it together. From the 92-95 Z07 setup which was the same all those years according to our C4 Suspension Chart. I already have the rear 24mm sway bar and the FX3 setup. I need the the below:

1. Front 92-95 Z07 spring 90.1 (n/mm) FSK spring code
2. Rear 85-95 Z51, Z07, R9G spring 57.2 (n/mm) NYU spring code
3. 30mm Front Sway Bar 85-95 Z51,Z07,R9G
4. HD Lower Control Arm Bushings

I think that is all. The rear spring NYU and the 30mm bar should be easy to find. The front spring and lower bushing, a bit harder.
Would the 88-91 Base front spring at FHA 93.1 (n/mm) be an acceptable alternative to the Z07's FSK, they are very similar.
Also, other than finding low mileage good condition lower control arms from a 92-95 Z07 car, is there an aftermarket alternative or even maybe the lower control arms from a Z51 88-91, 96 car?

I'm not sure on the early 85-87 Z51 30mm front bar fitting on the later suspension? I don't think they would. I know the rear spring should be compatible from 84-96, fit wise.

Also, since I have the FX3, lets say I get a Z07 setup under my car, would it be worth while to add stiffer Moroca valving to the Bilstien shocks? Also, would a FX3 Motor sports Controller be a good idea, or would these parts or a combination thereof, make the otherwise good Z07 setup too stiff for good handling. Lets face it, too stiff and instead of absorbing bumps mid-corner in a parking lot, you go skittering off because the suspension cannot absorb the hits and bonces too much.
That being said, the mods to FX3 shock might be out of the question for B-Stock maybe BSP? Enlighten me on your thoughts for the shocks anyhow!!!

Jason

Never pass up an opportunity to have an instructor/shoe ride with you, and every once in awhile let a hotshoe take your car out, you'll save a ton of money on mods after you see what your car can already do in their hands.

If there is ever an Evolution Autox school in your area, it's definitely worth taking. And remember to have fun.

Solofast

To remain legal in stock you can't pick and choose what year or what springs at which end are correct. You have to upgrade as a package. That means if you want to go to a z07 spring in the back you need to put a Z07 spring in the front. Same thing with the bars, if you have Z07 springs, then you need to have a Z07 rear bar (front bars are free).

Most all serious autocrossers get rid of the FX shocks and go with the yellow Koni sport single adjustables.

You can't buy the lower bushings, you have to get the complete control arms and any new ones that you buy won't have the stiffer bushings in them, all that you can get are the soft ones. Not sure if old stiffer bushings (if you can pull them off of an old Z07 car) would be any better than new soft ones, so you are SOL on that aspect.

Get the Z07 springs and bars, get the car aligned, take all of the shims out of the front alignment to get all the negative camber you can get. Set the rear at -1.5 degrees of negative camber and toe the rear in about 1/8 of an inch, toe the front out about 1/8 of an inch. Get the Koni's, a good set of street tires and then get as much seat time as you can get.

Enjoy!!

shotchkiss

Front bars and springs are different 84-87 from 88-96, the rears will interchange to all years. Later model 30mm bars are hard to come by.

Shocks are free in stock, don't know if the FX3 changes anything with that, if you can switch, Koni yellows work very well.

1991Z07

I had my FX3 shocks rebuilt by Bilstein to Rippie specs and bought the Rippie FX3 controller.

Long story short, everything is bumped UP one notch...soft = sport, sport = performance, performance = STIFF.

As long as the system is still operational, it's nice to have a daily driver able to switch to a softer shock setting by turning the **** in the console instead of messing with the Koni shocks directly.

You can check Dino's Corvette Salvage...they may have a Z07 car with all the parts for you.

It IS addictive, isn't it?

93Rubie

I happened to come across the website for that school. They have a class at BeaveRun next April. I am considering taking it.

I had the Solo Chair of my local SCCA chapter (who has a 93 Corvette in BSP class) drive my car with me riding shot gun. That particular day FTD was 61 seconds on race tires. He ran a best of two runs of 66 seconds on my Kumho Escta SPT's. He said there was more in the car, especially if I went with race tires. That is basically bone stock with a good drive, I was impressed. The car has a LOT of potential, if I can learn to drive the car TO its potential.

93Rubie

That is what I was thinking, by keeping the FX3, I can enjoy the car on the street more. Keep in mind this car is multi-purpose, its gets raced both auto-x, drag racing, car shows, cruises, etc...Nice to be able to have some flexibility in the shocks anyhow.

Thanks to all for the reply's so far, big help. Keep'em coming.

1991Z07

P.S. You'll NEVER find a LCA with the high durometer bushings in it new. They phased them out of the inventory YEARS ago...

Sourcing the bushings will be a PITA...maybe find one from another application that is the same size? Regardless, you'll need to do a lot of leg work to get there.

NCCC let us go to urethane bushings because the source was no longer available for the Z07 bushings. You might want to give your sanctioning body some thoughts on that, since only an original Z07 suspension would still have those bushings in it (and being this old would be dangerous to use).

I swapped mine out after 5 years of autox, and they were wallowed out something horrible. Couldn't imagine what a set after 15+ YEARS would look like.

shotchkiss

Just run in BSP, so much more you can do, then you'd be legal with poly bushings, cut airbox lids, and replacement shock controllers. Plus then you can actually run a decent race seat in the car.

93Rubie

I'll probably wind up doing that, but for now...this is basically research for the future. Besides you basically cannot get rubber bushing for C4's anymore all anyone has is poly. Any recommendations on that front?

l98tpi

My 2. Don't worry about changing any parts out now. Learn the limits of your car and learn how to read the tires. The tires are the most important part on your car. Learn to negotiate each turn on the course and how to take the best line to get the most speed out the turn. As far as alignment, find someone in your area that can align and corner balance the car. When it is time to purchase tires again, the Kumho XS is going to be one of the best street tires for autox/track. I bet you could probably pick up 2 seconds just with those tires vs those SPT's. Good Luck and Have Fun.

93Rubie

I hear ya and realize that stock is faster than I am. Sometimes I get too excited about things and get ahead of myself. However, I have a better idea of what I can and someday probably will do so...nothing lost only gained knowledge.

mashinter

I have a '92 Z07. The front spring is coded (molded-in) FSB not FSK. I assume the guts are different than the '88-'91 FSB but the mold used is the same...? (I assume the '92 FSB spring is softer than the '88-'91 FSB because they went from a 26 rear bar to a 24 rear bar for '92.) The build sheet shows FSK and that was probably on the (long gone) paper tag on the front spring.

Here is a picture of the underside of my LCA. I am guessing that the '88-'91 arms are the same as my '92s. I understand the stiffer bushings (with or without LCA) were never available from the dealer.

Solofast

The 26mm rear with the high rate rear spring was a mistake. It had nothing to do with the front springs. Somebody in the Corvette group increased the rear bar diameter because it was already in the parts bins (for the ZR-1) and he thougth it would help the car in autocross. Remember, only about 750 Z51/Z07 cars were sold each year, this was a pretty small number. Since the parts were already in the parts bins for the ZR-1 it was simply approved without any real testing.

It was only put in for one year (1991 although some data sheets show it in the package for both 90 and 91, that is incorrect and Hib Halverson has corrected his master sheet to reflect this, here is the link to the correct chart:

http://temp.corvetteforum.net/c4/gcr...sion_chart.pdf).

This higher rate rear bar, with the high rate springs caused the rear of the car to jack because of too much combined rear roll stiffness. It worked on the ZR1 because that car has a lower rate rear sping.

When the LT-1 motor was being developed for the 92, they did some autocross testing to make sure the motor wouldn't starve for oil, and they quickly changed back to the softer bar.

93Rubie

I can't even find FSB according to this chart? IDK? Interesting tidbit any how.

This is yet another Hib Halverson document.

http://www.corvetteactioncenter.com/...ion-chart.html

93Rubie

Speaking of oil starvation is it necessary for LT1's to be run 1/2 a quart over to auto-x? I could understand for track use with high G turns but auto-x? IDK?

Solofast

We always ran these motors 1/2 a quart over. It was cheap insurance.

While in most autocross events you aren't at high g for a long time, every so often you get a full 180 or 270 sweeper, so we just did it as standard procedure.

mashinter

I'm sure the ride and handling experts at GM would love your interpretation of their expertise...

Nope. The jacking effect is proportional to the rear roll center height, which is the same on both cars. The rise of the rear (due to the jacking effect) is inversely proportional to the spring rate; softer spring = more rise.

Sorry for the off-topic excursion, 93Rubie. Good luck and have fun.

NOSLO6

They're great. Top quality instructors and TONS of seat time. Great bang-for-buck there.

93Rubie

So 5qts. would have no ill effects for street use as well???

Just in case anyone was interested here is the results from my last event. I'm number 45 on the list. I'm not fast, but i beat some folks. I even beat a the C6 lower on the list, it was a convertible looked way slow on course I guess this shows it.

http://www.steelcities-scca.org/Auto...Event9_PAX.pdf