Different designs of inlets and outlets dramatically effect the performance from Roots superchargers. Original designs for non-boosted flow used large inlet and outlet openings. Shrinking those openings for boosted flow improved performance by reducing reversion from the blower manifold back into the blower. Moving the openings forward also improved performance by restricting the amount of fuel flinging out the blower inlet that would otherwise interfer with inlet flow. Roots blower sizes are featured in Fuel Injection Racing Secrets along with a detailed description of how they increase performance. They are detailed in a math section on how to detemine nozzles and jetting.