Pulley Ratio Calculator: ((14.7+ Boost in psi)/14.7) X (engine liters/2)/supercharger in liters)=Pulley Ratio at sea level Pulley ratio formula for a crank driven supercharger: (crank pulley size /supercharger pulley size)= pulley ratio Blower sizes: General information that has been published by Jim Bell:1 psi boost requires 1.5 octane (minimum) 1 psi boost = .5 point … Continue reading Roots or Twin Screw Boost Calculator