Someone suggested that because the supercharger is geared to the engine, and because the supercharger is theoretically turning at the same speed as the engine, there will be no manifold pressure loss. This isn't true. Bear in mind that because of the use of a constant speed propeller, one can increase manifold pressure substantially above barometric, with the use of a supercharger, with no increase in RPM. RPM, therefore, is not the only determining factor regarding manifold pressure, when a supercharger is used.
Yes, the manifold pressure can be changed by opening or closing the throttle, with the same RPM - but that manifold pressure isn't changed by spinning the supercharger any faster or slower. As long as the prop can provide the same torque to turn the engine at the same speed, the supercharger will rotate at the same speed, and if the throttle hasn't been changed, the boost will be the same. N'est pas?