Get my car to launch better...

There's some great info here. I'll add my take on pinion angle setup. Pinion angle is the difference between the centerline of the transmission output shaft and the centerline of the pinion gear UNDER LOAD. Meaning when you're accelerating they should be parallel. This does not mean pointed at one another. It means parallel. My method of determining where I'm starting from is have the car on it's tires but off the ground, with some weight on the driver's seat (for me thats 225lbs), plus a 1/2 a load of fuel. U use a magnetic protractor on the macined flat of the front slip yoke and recor the angle. Then do the same with the flat of the pinion yoke. The difference is the starting point. Under load, the pinion rides up the ring gear, pushing the snubber up on the floor. It depends on your car but my bsaic specs are for street: point the pinion down about 2-3°. For road race (stiff suspensions, less body movement) down 1° or less. For drag racing (lots of body movement, supple suspension)down 3-4°. As an example or a typical drag car...If your trans output is pointed down from parallel to the ground say 4°(big block and motor plate) and the pinion as measured is 2° down from parallel with the ground(SS springs w/ the shorter from segment), that means you need to shim the leaf spring perches or cut and relocate them to get the pinion down far enough to get proper pinion angle under load. In this example's case that would be 2°. Leaving the pinion "down" 4° from the trans output at rest. Pinion angle on a stick car is as critical as the shock package and clutch choice to keep from breaking stuff. Video the car and see how much the body seperates, then duplicate it witha floor jack, and you should be close to what your car is doing under load. You may find you need more angle... Or less.