subtlez28

My 84 LS1/T56 swap car is intended to be a street legal, but track focussed toy. I'm going through the car, and the rear suspension is my current focus. I intend to run 17x11 ZR1 knock offs and 315/35/17 Kumho XSs.

It has an 84 Z51 spring, Koni shocks (orange), and a 26mm rear bar already. The bushings are SHOT!

I think I am sold on the rod ended toe bar kit as the stock parts are crazy expensive. Just a matter of deciding brand (Banski, VBP, Gulstrand...).

I'm up in the air on the camber arms. I'm thinking some ploy bushings would do, but maybe less compliance in form of rod ended parts. I'd like to hear advise/experience on that.

I am leaning toward keeping the stock trailing arms and going poly or poly-graphite bushings. I figure a small amount of compliance there will be ok, and may even help not "shock" the tires on launch. I'm thinking they pretty much travel on a single plain, and require minimal articulation.

So are my current parts ideal (or close). Are my theories in line?

I really don't car about road manners here, and will spend money if needed. I just don't want to drop $ on parts that will not create a noticeable difference.

I will run street tires for a while (or maybe forever), but an upgrade to slicks may be down the road.

Thanks in advance
-Shaun-

subtlez28

TTT

I've been doing some re-reading of old threads. It appears many disagree with the trailing arms traveling on a plain, and advised poly bushings will bind (especially at bottom out).

So, now I'm thinking (again) about rod end parts through-out the rear suspension.

However, I would still appreciate advise on the set up. And I would like to hear from those who have raced similar cars.

Sidney004

All of your ideas on the suspension are fine, I would add front offset control arm bushings so you can get more camber... but the real trick to getting a C4 to run with the big dogs is using slicks. With 315/35/17 Kumho XSs you will have a hard time staying ahead of a spec Miata and other lowly cars; the only time you will see a C5 Z06 is when you point them by. I am sure the "tire police" will be on patrol warning of the dangers and extreme breakaway characterics of R compounds, let alone slicks(not in my opinion) but I'm right.
My setup: 292RWHP, 32/26 sways, poly bushings, FX3 controller chip, offset front bushing, max front camber(-2 1/2 on one side, -3 the other side), -2 rear camber, heim jointed sway bar end links, rod ended toe bar and camber bars, (4) 18'" x 10.5 Z06 wheels with(presently Hoosier R75 305/645-18's), C5 brakes.

urtoslo

My 1994 C4 really liked coil overs. 600# springs in front and #400 in the back, 30mm sway in front and 26mm in back, very neutral handling.

subtlez28

Sidney, I hear you on the slicks. However I ran my 02 Z28 in a street tire class and was very competitive. I recently sold it, and intend to have the LS1 C4 take over. So I definitely want to stay in street tire for the season. I cannot imagine the C4 being anything but faster than the LS1 Z28. The C4 will have more HP, less weight, superior suspension, and wider tires.

I like the idea of driving to the track and back w no changes. I like the challenge of street tires. But mostly I like the open rules for our street tire classing. It is basically divided by displacement and boost (or lack of). There are a hand full of other rules, but no points counting and rule bickering. Just 140 or higher tread-ware, under 5.7 liters, and street legal, licensed factory produced car for my class (SS).

That said, my quest for speed may well lead to some Hoosiers in the future.

subtlez28

urtoslo: My understanding is early C4s are not so easy to convert to coil overs as late C4s. Otherwise that would seem a natural choice down the road.

subtlez28

Back on the topic of trailing arms...

I can see how poly bushings would cause bind. But what about new rubber bushings. I realize they require deformation to articulate, but I just don't see the deflection as such an evil thing (like I do for toe or camber).

Can some-one shed some light on this?

Rob31

I know of one c-4 that is as fast on KhumoXS as the Hoosier, His opinion , And hes runs it alot . Baldo Racing if I remember right
Spec Miata ?
Thats allot of camber with a short sidewall, love to know your wheel rates & ride height

Sidney004

1994 stock FX3 springs, stock front ride height, lowered in the rear only.

BrianCunningham

start thinking about a brake upgrade.

those '84 brakes won't last too long on an open track.

subtlez28

I agree. It came with later-model J55s on it, and I already have a C5 set up to go in its place (on 85 spindles).

Is everyone using so much negative camber? On my 02 Z28 (which I realize is a bit of an apples to oranges comparison) I ran -2.1 camber up front and it was actually to much for my 275/40/17 Toyos (550# springs 35mm sway bar). The inside of the tire was hotter after a few laps. I do realize different tires need differing camber though.

On an 84 will I be able to get -2 of camber by "shaving the spacers" up front?

CorvetteZ51Racer

I ran mine with -1.8 up front and -1.5 in the rear with poly bushings and the grip and tire wear was great (ran 11x17 A molds all around, 315F and 335R)

On the poly bushings in the rear, under hard braking, they definitely bind, so much so that heavy braking zones would cause the rear end to get light. Going with the spherical bearing pieces will eliminate that AND allow you to run less camber than with polys or rubber bushings. I honestly don't know if you could get replacement rubber bushings anymore (I know they stopped making the fronts a long time ago - you'd have to replace the entire CA), and the deflection of the rubber, especially if running R compounds, is significant.

Rob31

What is going to bind ? I have the same rear end getting light problem . Figured it was shock valving and a soft front end
Parts bind when you put weight on them , not when you take weight off .

BrianCunningham

The front's fine with poly, because the a-arms move on one axis

the rears need to move it two different axis
front & back as well as in & out.
They need some sort of ball & socket joint.

Jack your car up and take a look at the suspension



then there's friction,
the stock rubber bushings have stiff, look what the dogbones do when you take them off the car

Sidney004

I can't say for certain because I have no direct knowledge of an 84 but if you are freshening your bushings, offset bushings are a necessity. Removing spacers or shaving them won't get you close enough.
http://www.vbandp.com/C4-Corvettes/S...ffset+bushings

Rob31

I have had my car off the ground with the spring out ( checking camber curve) and was able to move the axle without too much effort . Had lots of resitiance in the sway bar bushings also .

astock165

What binds is the shoulders of the poly bushings. The frame bracket is u-shaped and you have two poly shoulder bushings in the trailing arm, one on each side. Take notice when you put the poly bushings in and then slide the trailing arm into the bracket. Is there any resistance? Does the shoulder of the poly bushing get compressed at all to fit inside the bracket? If the answer is yes, then you've got friction which will lead to binding.

Look @ the image below



If there's no friction in the trailing arm bushings then both the trailing arms should be hanging loosely under their own weight. Since they're not, that is friction, or "bind" that has to be overcome when the rear suspension moves up and down.

It's more prevalent on the frame side because the trailing arm bracket contacts both shoulders of the trailing arm but the same thing can happen on the knuckle side if the nut is tightened to a point where the washer compresses the shoulder of the bushing.

Some may argue that is what the spacer is for and that's correct to a point. However, the true test is putting everything together. If the spacer isn't long enough to ensure that the shoulders of the poly bushings are not compressed when all the hardware is tightened down, you will have some bind.

A rod end style rear suspension removes that issue from both the trailing arms and camber rods.

Crepitus

grantar2

First unless you have really gone through the engine, your not staying wih C5 Z06's unless the course is really short and your torque can help you stay close. The Kumho XS's are a fine start as you sort out the car, but R-Comps or true slicks are in your future. I am running primarily Autocross have XS's on my car, but the V710's are another world but at twice the price and 1/10 the life. Having said that pick up a set of used servicable R-Comps and Slicks for practice you will like it. I haven't found the breakaway that much worse, just your much faster when it happens.

Call Gulstrand, I really believe no one does the backend of C4 like he can. Also remember that the C4 will give you 2 degrees or less negative camber at the back, you want it all, but the bigger the rear tire i.e. 315s the more likely it is going to flex under load. Rear camber bars are worthwhile.

Have fun.

Kubs

I did not read through all the posts, but if you are focusing on stiffness in the rear look into the rod end kit by Banski Motorsports. Like Brian said the rear moved in two axis and the rod ends provide little or no deflection but allow the rear to move in its full range of motion without any effort. It made a lot of difference on my when I installed it.