richiev88

What mods are need to the vette rear suspension for serious road racing / circuit track.
The car is running a 70, 572cu alloy BB, Tex racing box, Harrop 9 inch diff conversion.
Whats the best, necessary mods to get the rear end to handle without geometry changes due to loading. the car has full cage, will be running slick circuit tires

Thanks

Solid LT1

Look up Corvette 6 link or Greenwood 5 link for some information. I am presently trying to close a deal on the Greenwood 5 link set-up right now.

You need to eliminate the toe steer of the stock IRS geometry and a 5/6 link suspension is the only real solution.

If you mount differential high into Xmemeber you will help eliminate toe out (most dangerous condition) from the Vette IRS.

I'm interested in your "Down Under" IRS set-up maybe you can post photos?

TheSkunkWorks

Before I offer anything that may be moot...

1) Are you going to have any rules restrictions?

2) What kind of budget limitations?

3) And, does your 9-inch conversion retain C2/C3 IRS suspension?

richiev88

Hi,

With regards to rules, they are fairly relaxed, would need to retain a IRS set up, but can go to link system.
Budget it no a major concern as all fabrication work is done in house, and this car has some $$ spent allready.

Yes the 9 inch is just a alloy housing made to bolt in by Harrop engineering in Ausie

Thanks for the input

TheSkunkWorks

Not to assume anything, if you haven't already gone thru the Chevy Power book's Corvette Chassis section, I'd do so now, as it does cover a number of fundamental improvements you need to have performed.

If you can swing getting one, the Greenwood 5-link would be very nice. FWIW, Guldstrand also has their own version of a 5-bar link. DragVette's 6-link does not have comperable geometry to either of the above, so IMCO it's best left to the strip.

Should you end up keeping the C2/C3 TA's for any reason, I'd replace the rubber bushings with sphericals or, better yet, Johnny Joints, and raise your diff enough to keep the half-shafts from dipping below level during bump.

There's more to this, of course, but hope we've pointed you somewhat in the right direction.


TSW

richiev88

Thanks,

We have some experence building road race cars, but is always much to learn from thoses who have do it before.
Appreciate the advice

Richie

TheSkunkWorks

BTW, I'm still giving a lot of thought to that dog box...

richiev88

It really depends on the person with thoses boxes. I don't mind the noise and the race shifts, some would not like, few years ago it was the only reasonably priced box for a big HP. I think running a pump and filter would be a good idea if you were going to do many miles, keep the debris out of the oil

gkull

I wrote a long post and it went away

I ask what do you really intend to do? Because for a few grand more you can buy a sequential tranny. Even at 2850 pounds braking is a major mod. I have air ducted big brakes with 295F and 335r R1 slicks.

You need to go to a track and see what BP and GT1 cars are doing. I race with them and run 10-15 seconds off the big guys arounds our local 4.2 mile track. For under $100K you can buy a 6-12 year old full on GT1 race Vette with spares

richiev88

The cars a long term project of a good mate of mines. He has had it in various forms for 20 years. Used to be raced as a L88 replica, as things broke its slowly been upgraded.
Its got big vented brakes, dry sump, ect.
Its going to be a car that gets raced once or twice a year, sequential trans is out as they have to stay std pattern. Rear end has always been a issue, so trying to get it sorted.

gkull

You need to look into 6 link IRS setups. Our C-3 are 4 link Two lower struts and two trailing arms. The six link adds two more struts above the halfshafts parrallel to the lower struts.

richiev88

Thanks for your input.
Muscle car racing is getting very popular in New Zealand, as well a several tin top series, canams and f5000s are quite big now

http://www.centralmusclecars.co.nz/

TheSkunkWorks

gkull, what 6-link are you referring to?


I ask primarily to make sure the OP is aware the one I mentioned previously doesn't do anything about toe-steer, as it retains the OEM TA layout. Also, it should be noted that parallel equal length upper and lower control links place the IC's at infinity, yielding zero camber gain in bump; great for drag racing, not necessarily so for road racing, IMCO. In any event, I hope that helps to explain the reasoning behind my earlier comment on geometry, whatever such system is in question...

richiev88

Slightly of topic, has anyone ever run spherical bearing in the front of the trailing arms ? Perhaps a threaded nut lock system instead of shims ?
I replaced my rear leaf spring bushes in my 70 RR camaro, with sherical bearings, it stopped the bushes binding as the axle moved through its ark...

Solid LT1

Dick Guldstrand makes a threaded toe adjuster for our Vettes but, it is best installed with the body off the frame. Spherical bearings are also on Guldstrand's site and Herb Adams made them for a while. Look up wikipedia for the C3 Corvette faq site links for more suspension information.

The Elliot Forbes Robinson L-88 C3 Vette that was the last big bore A Production SCCA champion in 1978 did so on stock trailing arm bushings.

Here is a link to Guldstrand: http://www.guldstrand.com/mrcorvette.asp

richiev88

Yes sometime you end up going full circle with these mods, no pont in re inventing the wheel. Thanks for your thoughts I shall have a look up those sites you suggested.

gkull

BB72

Thats similar to what I made, very anxious to try it out later this summer. All custom made with heim joints and the smart strut bracket on the bottom.

TheSkunkWorks

It's worth noting that just relocating the upper link from the half-shafts, while relieving them of the task has some merit, isn't necessarily going to improve the rear suspension's dynamic geometry. Road racing and drag racing are altogether different problems, and the full scope of maths which come into play (camber curves, toe-steer, roll centers, jacking forces...) when setting up for the former aren't so straight forward as they may appear at first glance. Just sayin'

BB72

It's very difficult to address the toe issue without major changes. The camber issue is improved with the upper strut rod, and reliability. The 6-link was tested in one of the Vette magazines and offered a significant improvment over stock.