I've grooved a set of Bilstein Sear Point shock bodies for coilovers and will be installing them on my C4. I've got an idea of what I want to achieve, however, I'm still not concrete on the particulars.

I've got an '84 tub with later model outboard suspension front and back, except I have retained the '84 upper control arm. The tub has been lightend, the engine moved back and down. Corner weights with driver and 1/2 fuel load are:LF 651, RF 623, LR 633, RR 601. The application is for roadracing.

The car seems too stiffly sprung, especially in the front, it chatters across the corners. I wish to go down (from stock Z51) spring rates and also reduce the shock rates appropriately.

The current valving is F: 360 rebound/135 bump R: 540 rebound/360 bump.
The current spring rate is ?does anyone know? I think around F: 425#/ R: 375#?

I have found suitable Bilstein racing shocks valved at 300/100 for the front.
I could not find racing shocks that would fit within the measured ranges of compression and extension for the rear, so I suppose I will keep the rears as "production", forgoing the sperical end mounts and perhaps just revalve them.

I think a reasonable spring rate might be F:400, R:350. Any ideas?

I also have questions like:

--How far forward do you need to move the rear upper mounts to keep the springs form hitting the halfshafts?
--Can you fit a 2 1/2 coil spring through an '84 upper control arm?

Suspension Guru's chime in. speedj


[Modified by speedjohnson, 11:19 PM 6/20/2003]


[Modified by speedjohnson, 11:47 PM 6/20/2003]

 

I can give you a few tips:

1. The 2-1/2" springs should work on the front of your '84, my '85 has them.

2. 350 will probably be too much for the rear. I started at 300 and couldn't get enough weight transfer when applying throttle. I now have 250 rear/500 front. I had 450's up front and a zip tie around the shock rod told me they were bottoming out.

3. You will avoid a lot of headaches and jerryrigging in the rear if you get the heim-jointed trailing arms. I have the Guldstrand set and it allows you to move the trailing arm a lot closer to the knuckle, increasing spring clearance. If you use the stock trailing links you will have to shim it and your shock won't travel through its intended range of motion. Here's a few shots of the trailing links: (BTW the contact marks on the spring are from before I had the heim jointed trailing links)




And here is the length of the shorter bolt vs. the stock bolt for the trailing link/knuckle (it doesn't appear that much shorter, but its the shoulder where the threads go to that's important here):



Hope this helps. :seeya


Oh, Here's why you need the shorter bolt - the Guldstrand hardware uses spacers and the stock bolt. Also, when you go to coilovers you reverse the direction of the bottom trailing link-to-knuckle bolt. The head of the bolt takes up less space than the threads and nut.




Also notice that the bottom of the shock is spaced away from the knuckle. You can see that the shock and its lower mount are not perpendicular as they should be. If you compare the rubber bushings of the left suspension to the right suspension, you can see that the shock is kinda in a bind on the right (last) photo. The driver side which has been corrected needs no spacers and the shock travels smoothly in the direction it should.
:smash:


Oh, and a simple fix for a rubbing spring (sounds like a no-brainer but it didn't come to me immediately and I think i'm OK) but turn the springs! I had trouble with the front sway bar rubbing and just a simple turn of the spring and it doesn't touch. Also, if the tires are off you can use a large pry bar to take weight off the spring adjusters enough to turn them by hand, making adjustments a lot easier. Not much good for scaling, the tires get in the way. Maybe a set of thinner tires for scaling/storing/moving the car around the shop? Hmmm.... :rolleyes:


[Modified by vetracer, 6:22 PM 6/20/2003]

 

The pictures really help, thanks.

You are running 250# rear 500# front? Is this a drag or a roadcourse setup?

 

Road course. Firebird, PIR, and COULD have gone to Fontana and run their road course/speedway this weekend, but work got in the way.

 

I've just checked out your cars on you signature page. They are Awsome!

One more Q? Are you using 2 1/2 x 8" springs or 2 1/2 x 10" springs?

Your help has saved me a ton in development and wrong choices. Thanks! sj

 

Thanks for the compliment. They are 10" 2-1/2 inside diameter springs from Coleman Machine. Looks like I paid 63.00 each. I've got the invoice out, their number is (906) 863-8945. No website info listed. They've got a great catalog for racing parts, too.

 

So is all you need for coilovers shocks that have been grooved for them, springs, and different trailing arms for the rear??
:lurk:

 

Yes. The factory mounting points are used. :cool:

You will of course also need the spring retainers and may have to spread out the flanges on the sides of the top front shock mounting location slightly to make enough room for the spring to slide into it. It won't be noticeable, though.


[Modified by vetracer, 7:08 PM 6/20/2003]

 

where do i get the different trailing arms at?

 

http://www.guldstrand.com

:seeya

 

Hey speed, just sent an IM on where you placed that snap-ring groove on your Bilstein's.


[Modified by superlund, 9:11 AM 6/22/2003]

 

Exotic Muscle also has the trailing arms, camber rods and toe rods.

These 10 inch springs just barely fit rear the shocks. They are almost too long. You have to preload them and the coilover mount is turned all the way down. The ride height is about right when the car is let off the jacks, but really no adjustment room to lower any more. I wonder if an 8" spring would work or if it would coil bind? Any one using 8" springs in the rear?

 

Exotic Muscle did the original coil-over swap on my car, then I ended up changing springs after spending some time on the track with the car.

You are right about the rear springs. Maybe an 8" spring WOULD work better, but I don't know, never tried it.

 

Thanks again for the set up advice. I've got the body off the frame now and have been working on lightening the car up some more, cutting off non-used tabs and structure that is redundant to cage. I've taken now 127# off the frame and another 28# off the already gutted fiberglass body. While I've added back some 33# in additional bracing ... I've got the frame/cage package down to 525#. Wow! This is really going end up being a light car this time around. Last time corner weights were all low 600's with a total weight coming in at 2508#. Now mid ?2400's?

To deal with the rear shock mounts, I moved them forward 1" and sunk them into the frame rail; moving them up another 1/2 inch or so. This gave me alot more clearance with the trailing arms/ halfshafts. It looks like I still have a good amount of suspension travel, approximately 2 3/4" into bump and 2 1/2" in rebound. The bump steer really was off alot, especially after about 1 1/2" bump ... those adjustable toe rods really worked out sweet!

The front shocks arrived today. They are a Bilstein oval track racing shock. The shortest I could find was 16+ inches extended and 11+inches compressed; about two inches longer than stock, so I relocated the upper mount to a stiffener bar that runs horizontal to the forward frame rail, which looks like it will work just fine. The shocks are linear valved at 300/100 (20% less that Sears Point valving) and I will try them with a 400-450" spring to start.

How did you deal with the front sway bar? It looks like it will interfere with the front coilover and you would have to move it forward. The problem with that is the bar will limit turn in at full lock, as it hits the inside of the rim. Did you move yours or did you just get creative with the end links?

I'll keep you posted on the final result, we've got a double regional July 4th weekend @PIR.

In the front


[Modified by speedjohnson, 9:55 PM 6/23/2003]


[Modified by speedjohnson, 9:59 PM 6/23/2003]

 

If your car weighed 2508 lbs with a full cage, that's amazing. Mine is 2820 with no driver or fuel and thats with a fabricated race interior, lightweight hood, lexan windshield and rear hatch, no bumper reinforcements, ect.

Moving the top shock mount would definitely help half shaft and trailing arm clearance. Sounds like a great setup! :thumbs:

Oh, your question about the sway bar: this is where turning the springs comes in. If you turn the spring with the car at rest and suspension settled so that nothing is touching you should be fine. As far as I can tell, the sway bar isn't making contact with the spring even though it APPEARS that it would.

Do you have the 1" aluminum spacer blocks that go between the frame and the bushings like what Guldstrand sells? Apparently this block improves the geometry of the sway bar and makes it more effective, although I don't remember exactly how.


[Modified by vetracer, 10:53 PM 6/23/2003]