I will ask for any advice. 3,138 lbs car with driver. weight bias 48.6% on rear wheels, 120 lb rear springs, double adjustable shocks all four corners, anti squat set at 116% instant center length 68 inches 14 inches height. Car ran last year 6.0 @ 114 mph in the 1/8 with the converter slipping. Shift light never went off the entire run after launch. New converter problem fixed. Car leaves perfect, lifts the wheels about a foot and carries them out a little way. 1.35 60 foot, the Issue is the car wants to spin the tires at the end of the 1/8 mile. Tires are a couple years old but have lots of meat on them. The four link was put under the car 20 years ago. I am thinking for maintance the heim joints need replacing. Everything appears tight no cracks in brackets. My main question is would a longer lower instant center help plant the tires down track? Any other ideas on fixing the problem of breaking the tires loose down track? Engine makes 800HP and about 750 ft. lbs of torque.

3100 @ 800HP should be a 9 flat @ 150 in the 1/4 player. 5.70 in the 1/8. 60' is a tenth slow, at least, all based on the HP number. Weight bias is better than a lot of them.
Was this on a happy dyno? Not being a wise guy. Just crunching the numbers. If it's really 800, something is going on in the car. The numbers you give work out to be maybe 670 HP at the wheels on my dreamwheel.

68" is way too long for your HP. 14" is way too high. You have no downforce down track. Your bars are basically parallel.

Looking at your graph - take the bottom bar out, put it in the bottom hole on the housing and make it level to 1 or 1 1/2 degrees down. Take the top bar out, move it up on the housing to get it 10 1/2 or 11" spread from the bottom bar. Put it in the chassis bracket at about 15 degrees down. Looking for 48-52" out or so. Figure on tightening the shocks some to control the hit, depending on what low gear is. This isn't overly aggressive. I have heavy stick cars that are faster than 6.0 set up like this. Dead hook, repeat like a dragster on tracks other people can't get down, will go high 1.20s in 60 if he gets after the clutch. He does have good shocks on it.

The 4 link brackets are high in the car so you are limited somewhat. Can the car be lowered? Doing that will get the brackets down and the geometry a little better.

I will ask for any advice. 3,138 lbs car with driver. weight bias 48.6% on rear wheels, 120 lb rear springs, double adjustable shocks all four corners, anti squat set at 116% instant center length 68 inches 14 inches height. Car ran last year 6.0 @ 114 mph in the 1/8 with the converter slipping. Shift light never went off the entire run after launch. New converter problem fixed. Car leaves perfect, lifts the wheels about a foot and carries them out a little way. 1.35 60 foot, the Issue is the car wants to spin the tires at the end of the 1/8 mile. Tires are a couple years old but have lots of meat on them. The four link was put under the car 20 years ago. I am thinking for maintance the heim joints need replacing. Everything appears tight no cracks in brackets. My main question is would a longer lower instant center help plant the tires down track? Any other ideas on fixing the problem of breaking the tires loose down track? Engine makes 800HP and about 750 ft. lbs of torque.

Well to update this thread and help anybody that would read it in the future I installed all new hiem joints in the 4-link, a couple were a little tight, but I don't think they were a problem. I set the four link with 149% antisquat instant center 11 inches high and 41 inches long. Had to re-adjust bar preload to get it to go straight first. Hit is a little aggressive, but since I had my shocks set at zero on the extension, I went 10 clicks firmer and it calmed down the wheelstands a little, and it hooked down track. went some low 6's at 112 mph, in the 1/8 mile The track was prepped fairly well, so on a bad track it gives me some adjustment to make it hook harder.

Maybe a picture of the car would help, maybe you have a relatively high ride height. But still seems like you I/C is WAY to high still. If I were giving generic advice I usually would say start with the I/C pointing at the bottom of the firewall...But that is a very GENERIC place to start..

Not sure how you get it that high. especially with the IC that short. Even if the car sits high, the chassis brackets need to be installed to get the geometry right. On a backhalf car that sits high, Super Stock car, etc, the bottom of the chassis bracket will be hanging lower than the frame rail typically.

His graph looks like the housing brackets are up to date, but the chassis brackets are high in the car. Bottom hole of the chassis bracket should be ~ 8" from the ground. Maybe less depending on the design. If the bottom bar is level, the height of the IC is the height of the bar, regardless where the top bar is. I'd like to see what bottom hole on the chassis, next to bottom hole on the housing does to the bottom bar.

Did you get the converter fixed? Drive to the stripe under power?