Proportioning valve after conversion

ir3333 hints at a good point. The ideal proportioning also changes with the front to rear load distribution. Many pickup trucks have (or had) a finger that sticks down from the bed and acts on a prop valve (on rear axle I assume). With more load (bed sags down), it applies more proportioning to the rear brakes. If you are a busy mafia guy, regularly hauling more than one body in the trunk, you might need that in your car.

dusterdragracer, I'm not sure you get the point. "works perfect" doesn't mean the car stops, a correctly adjusted prop valve will skid the front tires just before the rears skid. Unless you are doing such skid tests, with an observer, usually on a wet parking lot, and tweaking the prop valve to find the limit, I don't know how you know you are at the perfect point. Of course, most people don't and "good enough" is certainly acceptable, and "perfect" is a target that always changes with all the variables mentioned.