ram was always useful. Say for instance you are flying at 25,000ft where the air has a pressure of 11.10lbs/sq in (from old chart) if your forward speed can raise the pressure in the intake duct just before the supercharger or carburetor by just ONE lb/square in ch the plane will think it is flying at 23,000ft. If you can raise it by just over two lbs/sq in the plane will think it is flying at 21,000ft. It doesn't matter what kind of supercharger system is being used.