Cobra Jet guys please

[Bracketstang]

New guy here. I'm not class racing but I'm running the S197 chassis in a no-box bracket racing class looking for some experienced help from folks with experience on the first gen (2008 3-link style) Cobra Jet cars.


I have a 2007 Mustang GT that I bracket race. The car has an aluminum headed 565" big block chevy mated to a powerglide with a transbrake. I have QA1 Proma Star double adjustable front coil overs with 150# springs (9 clicks of rebound and 9 clicks of compression), lightweight front brakes, aftermarket k-member, tubular a-arms etc for the front end. The rear end still has the factory 3-link with aftermarket adjustable control arm mounts at the body and the rear end. BMR drag springs in the rear with Viking double adjustable shocks. I'm running 30x9" Hoosier D05 slicks at around 15psi. I've also run 29x10.5W stiff wall tires at 18psi with the same results for what that's worth.


1.80 gear powerglide
6000rpm converter
3000rpm launch rpm



The car is stock-appearing but has as much stuff pulled out as possible to get the race weight down to 3340 with me in it. CoG is @ 57.25" ahead of rear axle.



I'm specifically looking for some setup tips. My car has been deadly running high 5.70s to low 5.80s in the 1/8th @118mph with 1.25-1.27 60' times. That said, it will randomly spin the tires at the hit at the most inopportune times costing me a round (usually a final or a combo race). Watching the video, the car will initially launch, pull the front end off the ground (maybe 3" wheelie on this car) and the unload the rear tires while the front end is still in the air and spin.



The rear end setup currently puts my instant center at 49" ahead of the axle, 9" above ground and 95% anti squat. Rear shock settings have been tested all over the place but I've found that 10 clicks of compression and 8 clicks of rebound seem to be working well for the "most of the time" scenario.


This is the longest instant center I can get without modifying parts. I think I can drill one more hole higher up at the upper control arm mount at the body and one hole in the lower control arm bracket at the rear end and end up with an IC length of 57", 10.25" off the ground and 93% antisquat. I don't have a lot of clearance around the rear tires for the car to squat a ton over the rear tires so I try to stay pretty close to the calculated neutral line.



Previously, I had been running an instant center length of 35" 8.4" off the ground with 125% antisquat but it was smashing the tire pretty hard so we changed it. I had similar results with this setup: the car would work really well until it didn't.



I feel like I've run out of combinations to test trying to make this problem go away. The issue is it's random and doesn't happen all the time so you get a false positive feeling because the car will run great most of the day or maybe even all day and then do something dumb out of nowhere at the next race etc.



I'm bracket racing, not heads up racing so I'm looking for consistency over optimized performance.


Thanks in advance for the help.