The proportioning in most mopar style master cylinders are a rated volume usually aprox,65%fr-35%r.This is volume only,not pressure.They were set this way for the disc/drum combos since large single piston or daul 4 piston calipers required more fluid volume than the small brake shoe wheel cylinder. Most race proportional valves are adjustable from 0 to 1000psi. most common manual brake systems working range is 400 to 600psi.