Umrswimr

I bought my '95 FE1 MN6 C4 coupe three years ago as a safer and cheaper DE alternative to my convertible C5. The C4 still has to be a streetable car, so keep that in mind.
Out of the gate, I'm thinking the car needs some significant help. I swapped the brakes for C5 calipers and carried over my EBC Yellow pads and Kumho V710's (on C4 GS wheels) from my C5. Basically the car is... not confidence inspiring. Aside from the braking (where I could routinely outbrake C6Z's), it lacks precision. Corner entry has understeer, midcorner and exit has oversteer. Body roll is higher than I'd like and the suspension itself is loose. I want my C4 to handle like my C5.

The first thing that I noticed was the lack of chasis rigidity in the C4. I added the R-D racing cross-frame and it helped... But there's still a lot of flex and vibration. Is it worth it to add the camber brace and the harness bar? I don't want to add the S-T bar because it eats up too much of the trunk. Gotta compromise somewhere, I guess. I'm worried that stiffer springs will only make this worse.

C5 has: Z06 springs, sway bars, and Koni SA shocks.

I added Bilstein sports to my C4 and there's still a lot of movement. I can "bounce" the front of by C4 by hand by pushing on the hood. My C5 just compresses and doesn't let you develop a harmonic osc. The front C5 Z51/Z06 springs are ~525# whereas the C4 FE1's are ~417#. However, I think the biggest difference is the rebound control of the Bilsteins versus the Koni's.

Basically I'm looking at the full vbandP X-treme suspension kit as well as the Polyurethane front end rebuild.
Anyone have any feedback on this system? Am I better off building my own system from other parts? I know Brian Cunningham is looking at various rear-end configurations- do I need to replace anythign back there besides the springs and sway bar?

I know the car is down at least 100 hp from my C5, but it's the suspension that has me the most frustrated...

TIA.

C4 has: R-D cross-frame, C5 calipers and rotors, C4 GS wheels, Meziere electric WP, Dewitts radiator w/EOC, FE1 suspension, stock drivetrain.

pipeliner1

Springs, Bars and bushings. I dont know what is in the extreme kit but the springs are pretty stiff.


Vette Brake extreme kit will fix alot of the problems you have. FE1 is to soft for these cars. If you really cant deal with the rougher ride get Z51 springs.

Match it with you preference of bars. 30/32F 26/24R

Bushings are old and poly is nice.


What your suggesting is a good start.

BrianCunningham

There's a lot of binding in the rear suspension.

That's why I'm replacing all the links with rod ends, they're also adjustable so I can play with things like rear caster.

I'm also replacing my springs and shocks with Penske coilovers.

Stiffness is a big issue, eventually I'll be putting a 6pt in, if not a cage, but like you I want to keep it streetable.

In the HP department, I'm putting AFR heads on a 383 with a blower.

Umrswimr

According to this, there is no Z51 between 91 and 95. 96 Z51 is the same as my FE1. '90 Z51 is a stunning 656# front spring. Holy hell!

Sidney004

My vote is for the poly bushings, the 32/26 sway bars, the RD cross brace and offset front bushings. Then an aggressive alignment(-2 1/2 front, - 1 3/4 rear) freshen up your V710's with Formula V compound, keep your hot pressures at 34 psi ft, 32 psi rear and it should do the business. It is similar to my setup, although I also have the camber rods, toe rods and front and rear heim jointed end links as well and the car feels great. Pay attention to the basics; fresh rubber and proper inflation pressures.
I will report back after my Thunderhill February 13th event on my latest demon speed tricks(300/660-18 Dunlop slicks on 10.5 OEM ZO6 wheels all around and a new fuel filter!)

pipeliner1

Its not Z51 those years.



Its Z07.


They tricked you

WNDOPDLR

Chasis flaex disappeared in my C4 with the installation of the ST frame-but you have ruled that out. I had minimal improvement with the cross frame brace and Dave Cooper, when he still owned R-D- suggested the ST frame. He was right. I am using Z51 sway bars front and rear and the adjustable height VB&P fron spring. Call them and talk to them about your set up. They will get you the right spring rate for your car. My car will handle with most C5's

mrc24x

The VBP extreme adjustable front spring is well worth the money IMO. I still don't have the front grip to get the car turned at entry/mid-point versus a C5Z but it's getting closer.....

0Randy@DRM

Have you looked into some of our products??? Our systems can help bridge the gaps in the performance between your C5 and C4.

Let me know if you have any questions
Randy
www.dougrippie.com

sperkins

Good reading....

pipeliner1

Lack of rubber or maybe a different bar?

0Paul Ruggeri

The first thing I would suggest is check the basics, ball joints, tie rods and especially the wheel bearings. If your car is going from understeer (typical for C4s) to oversteer in mid corner I'd guess there is some wear somewhere.
That fuel filter is good for 1.5 secs at TH Sydney

BrianCunningham

C4's are camber limited, that's why I'm going to adjustable a-arms.

Some like the the 275f/275r setup, others the 275f/315r setup, me I like the 335f/335r setup.

What's yours?

STEVEN13

Sorry to HiJack!!

What spring rate on these springs are you both running? I just purchased one for my 1992. They also included the rear bolts to lower the rear.

Thank you,
Steve

Aardwolf

For how much those springs cost, I'd just do coil overs.

At HPDE events, I haven't found my C4 to be really slower in the corners. I lose the most ground by the lack of HP.

Sidney004

Same here.

96GS#007

Some things that I did that will help...

- 1990 Z51 springs & sway bars
- Koni adjustable shocks
- poly bushings in the rear (except the trailing arms which will bind)
- poly sway bar bushings
- Global West aluminum "Del-a-Lum" bushings for the front control arms
- RD camber brace
- Shaved upper-control arm spacers for more negative camber
- Slightly lowered (~1") front and rear
- fairly aggressive alignment
- RD cross-bar
- Stock GS size wheels and tires
- CarboTech XP10 / XP8 brake pads (f/r)
- Brake cooling

The RD pieces helped with regard to chassis flex a little. You can tell the difference with them out. Having said that, the C4 chassis is still a wet noodle so you either have to get used to it or weld in a cage.

In the power department, a "mild" 383 is currently going together.

10.5Vette

Following this closely as I plan to auto-x my 93 this year. What is a S-T bar?

Umrswimr

Basically a rollbar.

http://www.r-dracing.com/stframe1.htm

Does anyone have pictures of their S-T frame installed? As long as it doesn't make my hatch useless, I'm willing to look into it.

I'm open to anything, Randy, as long as it's relatively inexpensive. What would you recommend?

And that's a very valid point. Most coilover kits I've seen run a lot of coin, however.

jaa1992

Its a 95, the bushings are what 14 years old now????

When I had the camber brace in it was better on the handling. After my last event in December the rear hub was out of spec so I decided this was the year to put in all new bushings, hubs etc. Good thing I decided that when we pulled that rear hub off it came apart in two pieces! I have about 95% of the parts clean, need to take the A-arms to the shop and have the ball joints and bushings done and it will be ready to go back together.

I'm looking forward to March at Road Atlanta to see how well she works!