I was watching a video of a corvette running 9's and I noticed every time there was any acceleration the rear end pulled way down toward the ground, I also remember the corvettes at the track doing this very well. What part of the C5 suspention make it bite so well and is there anyway to modify a F-body suspention to bite like that?

 

ive seen fast fbodys do the same thing............i think its the shock/spring setup, but someone here will know for sure.

 

The only Corvette I've seen run 9's was a C4, and it had a Fab 9 rear axle and a 4-link suspension. I don't think the Corvette IRS is very easy to set up for drag racing, but I don't know for sure. The new SVT Cobra's with the IRS have also not demonstrated a lot of capability on 1/4-mile applications. The first tests on the car produced horrendous wheel hop.

The dumpy, antiquated straight axle design on the F-Body has demonstrated a capability to run into the 8's with the proper setup.

 

Fred-
I'm not sure about 1/4 mile times- but from what I have heard the weakest link in the system is the halfshafts. after that they are good to some unGodly power/times

 

This may be the video Dave was referring to...

The link below is to a video of a C5 (MTI Z07) with IRS running a high 9. IRS MKIV Supras and 3rd gen. RX-7s are capable of the same thing.

http://www.z06vette.com/media/mtiz06.mpeg

The reason the Cobra has so much trouble is because instead of using a fixed rear subframe like the cars above, Ford tried to give the car a softer ride by mounting the subframe to the car with more bushings (highlighted in red and green in the second picture).

http://www.torquecentral.com/attachm...=&postid=66030
http://www.torquecentral.com/attachm...=&postid=66035

Unfortunately, the end result is that there's far too much slop in the rear suspension, a lot of drivetrain clunking complaints and inevitably, a lot of wheel hop. Apparently, the '03 Cobras are the worst of the bunch.

By comparison, here's a picture of an RX-7 IRS rear subframe (mine) getting an '03 Cobra 8.8" differential swap. The rear subframe bolts securely to the car at the front and top, and aftermarket Nylon or pillow-ball (roughly equivalent to a rod end with dust seals) bushings eliminate suspension slop (and wheel hop) completely.

http://www.torquecentral.com/attachm...=&postid=97334

Aftermarket bushings mentioned above compared to the OEM rubber bushings... (Nylon on right, pillow-ball in center)
http://www.rx7club.com/forum/attachm...postid=2046992
http://www.rx7club.com/forum/attachm...postid=2046999

 

If the rear suspension compresses on acceleration, the suspension does not have a lot of anti-squat geometry. Production C5 IRS would be that way because the suspension is designed for all around performance, not just 9.9 @ 144 in the 1/4 mile. Every suspension is a compromise, and the C5 in the video is very impressive, especially because it appears to have IRS. Moving the mounting points on the C5 is challenging, at least.

Anti-squat geometry uses drive torque to try to lift the rear of the sprung weight (body and frame) during acceleration. Trying to lift the body causes an opposite reaction which pushes down on the tires and increases traction. Any extra rear downforce due to anti-squat also means load is taken off the front wheels.

Anti-dive geometry at the front is used to help prevent "nose dive" during braking. "Antis" only work when torque is being applied to the wheels.

A drag only rear suspension like a 4-link can be set up to have large amounts of anti-squat. If it's well over 100%, the rear end lifts away from the tires and applies lots of extra downforce. A torque arm suspension like the F-body has a relatively small % anti-squat stock, but by changing torque arm length and front mounting point, and control arm pivot points, more anti-squat can be had. Unfortunately, handling can suffer, and power hop and brake hop may also increase.

FWIW, the low center of gravity of the Vette also minimizes the weight transfer to the rear tires during acceleration.

My $.02

 

Yep. thats the one. Ive seen F-bodys do it off the line but not in 2nd and 3rd gear like that.

 

FWIW, It’s impossible to build any significant antisquat into an IRS. Looking at that video what I’m seeing is a vette with a very stiffly sprung rear suspension that is squatting a little as it comes off the line. In a perfect world, with sufficient antisquat, the back end would come up (tires would get pushed down into the pavement) if it was launching correctly.