actual instant center measurements?

[summit]

I know this is a chassis question, but I already have rims and Wilwoods for my car so no sense posting in the wheels and chassis section. You guys would come closer to having actually measured your cars. I plotted out the measurements on my car on the computer last night and was wanting to compare to what others are trying. I have a stock suspension with locating brackets for the control arms so I can move the lower one around. The upper is fixed.
The front is QA1 coilovers so I can adjust front ride height easily.
A few specifics
3560 pounds race weight
48% weight on the rear wheels
3.7 rear gear, 28X10.5 slicks, turbo 400 trans
best 60 foot of 1.38, mostly low 1.4's
best 1/4 mile of 9.05@150

Currently car is set up with a IC of 53.5 long and 11.75 high
If I put it in stock locations it goes 74.7 and 8.42
I have available
47 and 12.75
53.5 and 11.7
57.5 and 11.0
68.4 and 9.5
73.8 and 8.5

I was under the impression that as you move the instant center center further forward you should also move it higher for better weight transfer. Looks like my brackets are forcing the opposite to happen. The car comes closer to "hopping" off the line when it picks the wheels up instead of lifting them and carrying them. Wheels come up about a foot off the ground, but it almost looks like the rear unload and drops them back down again to fast.
Something interesting to talk about. Any ideas? Are my measurements workable or do I need to see about doing major rework to get the numbers inline? Can ride height adjustments have that big of an affect? Maybe I should go the easier route and get some weight offf the front end!!

Greg Kring
Arlington, Texas
87 GN

 

[sixgun86gn]

Greg,sorry I have no idea what all of that means.I have a question for you about rear suspension though.

What rear arm setup are you using that allows so much adjustment?I have southside uppers and lowers and really don't think they will be capable of the ETs that I want to get in my car.I may be wrong?I would like a more adjustable setup and the southsides are a fixed setup.

Pat Smith

 

[turbobuick]

What dp you have the QA1 shock settings at and what are you running for rear shocks?

 

[summit]

Light as possible on the fronts. They now have drag shock 90/10 type available for the kit. I have the original style and even at the lightest setting it is still nowhere close to a normal 90/10 drag shock and transfering load. Rears are QA1 as well single adjustable. Somewhere there is a QA1 thread going on right now. I also see they are offering double adjustables where you can adjust bounce and rebound independently. a little pricey any way you go. I wouldn't buy them again without exhausting the less expensive routes. Now back to my original question..........

Greg Kring

 

[Joe Lubrant]

Greg,

Just curious, if your uppers are fixed, what is your pinion angle and how are you able to adjust it?

 

[turbobuick]

My car was doing the same thing. You need to tighten the front shock adjustment. Try 3 clicks, I droped from low 1.5's to mid 1.30's by doing this, literally and with no other changes, I also tightend the rear adjustment some but I would start with the front.

 

[summit]

Sweet. I have kept the front as loose as possible, but we have been thinking of trying to limit front suspension travel. I'll try tightening them up.

Joe--uppers are fixed as far as position, but both uppers and lowers are adjustable length wise so I can adjust pinion angle. it is set slightly negative right now, less than 3 degrees.

After more thinking we are going to try and lower the rear as much as possible and still keep tire clearance. That should effectively change the upper arm angles and raise the instant center and still have room to adjust to the lengths that I want. Race season is about to fire up again, time to start testing these theories. One step at a time of course.

Greg Kring