Someone knowledgeable please explain the difference between the 30/30, 30/40, and 40/40 non-ABS prop valves for people wanting to do rear disk conversions.

I don't quite understand it. My car has a 30/30 (rear drum). Why is it that non-ABS SI hatches have 30/40s (with rear disks) and Integra RSs have 40/40 when front and rear brake diameter are identical? I understand the pistons on Integras are minutely larger, but what are the benefits of switching, and is it mandatory?

 

I think it has been determined that the numbers on the valves have nothing to do about their bias. There is an old post somewhere that was about the numbers.

The difference in valves may also have to do with weight distribution. While the size of the brakes could be identical there could be a difference in weight distribution could be significant enough to call for a different valve.

The whole point of the valve is to make sure that your front brakes lock up first under hard braking and that the rear brakes still get enough force to still help without locking.