is this during startup? the car engages the supercharger at startup to warm the engine faster, also it spins at a ratio to the crank pulley and spins faster the higher the revs.
As for mods, I would start with a basic intake and exhaust, these motors react well to opening them up. From there, a tune, pulley, headers (supersprint or custom). You for more power than that you are getting into custom work, if you keep the motor you can either fit a large supercharger or go turbo. There are two turbo cars so far and both owners are members of the forum.