These adjustable upper rear control arms made by Buck Performance are a item for any serious road-racer or drag-racer. These are a bolt on upgrade, with direct fitment and no drilling required.
Even with the slider turned all the way in, the Supra is designed to run with at least -1 degrees of rear camber. While this may be good for basic street driving, it tends to eat up the insides of tires and is the opposite of what you want for drag racing and straight-line acceleration.
For drag racers, you are able to adjust the rear camber up to +10 degrees, allowing the tire to come into 100% contact as the car squats for launch. This gives you full contact patch with the pavement and the most traction possible from your setup.
For road racers, you can thread the knuckle in to achieve up to -10 degrees of camber if desired.
This arms are made to fit 93-98 Toyota Supra and Lexus SC300.