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Spring Lengths and Geometry Questions

Hi everyone, long post and will try keep it well structured with hopes of the best advice.

Did my second track day with my now stripped and caged track only S197. Last track day had horrible axle hop issues under breaking, thought I had isolated the issue to an extremely worn upper diff bushing. However, all new arms installed, completely spherical, set my rear lower arms almost parallel to the ground to reduce the ammount of anti squat I have and after my second warm up lap, got hard on the break and low and behold, horrible axle hop forcing me to overshoot the corner, glad we have plenty of run of room!

Back to the drawing board. My car is running AST 4150 with 180-90-61 front springs (7 inch - 513 lb/in) and 200-50-61 rear springs (7.8 inch - 285 lb/in). Since stripping and caging the car and installing a much lighter fuel cell, the rear has been sitting very high compared to for example a boss 302S measurements. And I think the upper control arm is sitting at a position in which it is still causing too much anti squat, even with the lower arms almost parallel. I need to begin by lowering the car back down, through a spring swap because my current 7.8 inch rear springs are maxed out on the vorshlag rear spring isolater/adjuster.

I found my current spring rates a little on the soft side and would like to go with 600/350 lb springs. Current spring working length is about 5.2 inches, to lower my car. I'm worried if I get a 6 inch spring for the rear which gives me adjustment room and a stiffer spring rate. I will run into issues unseating my spring when the suspension extends/unloads. Has anyone dealt with this kind of issue? What are solutions when not running a true coilover?

Thanks very much. Can helper springs be made to work in the rear somehow? With a linear spring in ast rear spring mount?
Can't see of a way to keep helper springs in place unless you weld a bucket to the axle. The easiest is to use limit straps or chain to hold up the axle.
they make a "soft" spring that will index the coil spring for you without affecting the spring rate. (I assume you're running coil overs)
something like this..

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