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FX3 Versus Z07 Initial Observations


Well-known member
Jul 19, 2009
1993 Ruby Red 40th Anniversary Coupe
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 balls 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.
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