Over this winter I swapped out my stock FX3 springs and sway bars for a set off a 236K 92 Z07 car. I know high mileage, but keep in mind GM wore out the testing equipment not the springs. No damage or delamination to the springs and mostly likely a lot of highway miles.

Anyhow, compared to the stock springs MUCH less arch in them. I compared them after I got them out. Rear is easy. Front is a PITA but doable. One interesting note the rear spring was coded NYU which is the 57.2 N/mm spring on 85-95 Z07/Z51 cars. The front was coded FHB which is "supposed" to be a 115N/mm spring however it was dated later than it could have been to be a 91MY spring. My guess is GM may have changed to the 90.1 spring FSK but still labeled it FHB. To further add evidence that this my be the case when I pulled my STOCK (untouched) FX3 front spring a 73.2N/mm, it was labeled FHA which would be a base spring from 88-91 as well as 89-91 FX3&Z51 cars. The 92-93 FX3 springs are "supposed" to be coded FSS. Interesting.

I did remove the front aluminum spring shims which dropped the front of the car about 3/8". Installed lowering bolts in the rear. I have a slight rake setup on the car. Very little but its there.

Stock 26mm hollow bar is a joke, very light. 30mm solid bar has some ***** to it. Heavy and stiff. Rear bar is 24mm solid. Which I already had.

Kept the stock FX3 shocks for now. As they where part of the package. Koni Sports are on the agenda in the next couple years. As is J55 brakes which I have but not on the car YET. DID NOT change to the stiffer lower control arms. I plan on going poly or ??? later.

Driving Impressions

MUCH flatter cornering, very little body roll in aggressive street driving. Front end sticks well and rear follows. I bet however the car will still understeer but it should be a push not a PLOW like the stock setup. Seems to have more front end bite and grip. Rear stays in place and gets power down on corner exit better. This may be partially due to lowering the rear a bit and putting the spare/carrier back on.

Rides BETTER than I thought it would. In fact it my just ride BETTER than the base springs/bars. Why? The car is less bouncy and lays to the road better. I noticed less difference between the shock settings. Before you could notice quite a bit but now its there but less noticeable. Sharp impacts like rail road crossing hit harder. The rest of the time the car is settled and smooth. I personally hate a "soft" riding. Most people would say a stock 2004 Chevy Malibu rides soft and nice. I hate it, car is jittery, not settled down. I like a taut, firm ride. I could do without the harsh impacts and flexable chassis of the C4 but I'll live with it, its quite survivable and doesn't bother me.

Transitional responses feel about the same which should be correct as to the best of my knowledge that has a lot to do with shock package. Not so much springs and bars. Those are more so for steady rate cornering.

Overall, I like it a lot. I cannot wait to really try it out come my first auto-x of the season. Combined with the new Dunlap Dizzera ZII's this C4 should handle a TON better and go much faster. I'm also adding more front caster and rear camber. To help reduce understeer and increase rear grip on corner exit under hopefully more throttle than last year.

 

I don't think you're missing *too* much action without the J55s.

having made the transition with what are marketed as aggressive street pads (stop tech's para aramid material pads) over unknown semi-metallics, Initial bite seems the same, and they really only provide noticeable increase when you're stopping from above say, 80 mph. Which of course, you rarely achieve on an autocross course.

I'm not sure if even the 12"ers would get hot enough that the directional veins would help you.

That said, for road-racing I'm sure they're well worth their mear $400-500 asking price, but for low-speed, they're functionaly the same as the 12" brakes. I only bought mine because I had stuck calipers and it was a 'might as well' call for another $100 over the 12"

 

One thing to consider with the FX3 shocks is to have them rebuilt with custom valve settings. Bilstein has a number of configurations for the FX3 shocks including the "Moracca" (?) setting that was designed by a CF member for Bilstein some years ago. Also talk to Doug Rippie Motorsports about FX3. They used to have a special controller that used replaceable custom PROM chips to further tune the FX3 system.

Going to the Z51/Z07 offset lower control arm bushing will allow for slightly more negative camber but you can also get upper control arms that are adjustable using turnbuckles. They are pricey but they allow for a wide range of camber and caster settings.

I would also suggest you look at the Banski Motorsports rear suspension packages. There are pieces that replace all of the stock arms in the back and use Heim joints for adjustments. I added them last year and it was a huge difference in how the rear of my 87 acted on autocross courses. There are a number of CF members that use them for both autocross and track use.

J55 front brakes will provide braking improvement, but down the road, how easy will it be to get J55 rotors? If you go with a C5 front brake upgrade, at least the components will be easier to find and more than likely cheaper too.

 

The only reason I want the J55's is for light duty track use. The 12" just are not really up to the heat of track use.

@C4cruiser. I have thought about revalving however with the Koni's I want I can adjust the shocks different front to rear to change the feel/balance of the car from day to day. I cannot do that with the FX3 system, no matter how good it is.

I can run soft in the rear for example and stiff in the front with the Koni's.

Yes, the off set bushings are something I want to do.

I like the Banski kit however I don't like the price and I'm in BSP as it is. Those would put me in BP. I'm not even on R-comps. so....while cool, the NEED factor is not there. Ditto the turn buckle control arms.

This is still a street car if I was building an all out track/auto-x car. You bet your life I'd have all those fun things.

You bring up an excellent point with the C5 brakes. I'm not sure they would fit under my wheels however. I run stock sawblades as "race" wheels.

 

I couldn't get my '92 sawblades to fit over the C5 brakes...and it wasn't even close.


Cool post on the suspension comparo.

 

Pricing and avability seem pretty stable considering these cars are nearly 30 years old already.

imo, I wouldn't really consider weather the parts will be available for the next 30 years, who the heck knows what will happen within that kind of time frame. Fossil fuel supplies may dwindle to the point that all of these cars become too expensive to operate at all.

 

It was good thought the C5 brakes. I suppose in the future that is an option with A-molds or C5Z06 wheels or ???.

Thanks.

 

Follow up, post 1st auto-x event.

HOLY CRAP!!!

Last year on FE1/FX3 the car PLOWED in corners, now it has a push but a very controllable one. Still some understeer but HUGELY reduced but the car is very stable. Mostly at low speeds did it understeer, and with almost full lock....yeah the turn(s) where tight at a spot or two....

Only ill use of the throttle does the rear end step out, in most cases it hooks up hard.

I was coming out of some hair pins today and nailing the throttle to the floor (smoothly) in 1st gear. Rear end just stuck like glue.

I take back what I said about transitional response, its crazy good. Car is very balanced in the slalom. I had to relearn when to turn in. I hit 9 cones today to prove it!!!!

I need more front camber looking at the tires, but its not too bad. I'll keep an eye on it, maybe halfway thru the season a flip on the rim might be due.

Those Dunlap Dizzera ZII's WOW, what a tire. In near freezing and wet conditions, it snowed a bit but none stuck to the ground or asphalt. Later it dried up.(around 40 ish or so, maybe 45 tops in temps) the tire had lots of grip, it heats up quickly, they where warm to the touch after 3 runs.

Wear so far is pretty good. Seems tire pressures around 33 (cold) in back an 35 (cold) in front give good roll over and grip.

Put it this way, I kept pace within tenths of a second of a near FTD C5Z06, his Hooisers in this cold, wet/dry stuff just did not have the traction.

The car needs more front negative camber (tire wear) and grip. If I had more negative camber I'll get both.

If you want your C4 to handle get some Z51/Z07 stuff under the car. You won't be disappointed.

Now if I can get those Koni Shocks on this car.....

 

Nice write up. The old rear spring of mine has a small linear chip missing out of it with bare material visible. I had planned on replacing it...... maybe a couple of Z07 springs if I have to go through the trouble.

 

Sounds like when I replaced my old suspension with the Z51 springs - better ride and control because the wheels weren't just flopping around at the corners any more.

Still need to get better bars though...............