A belted gear assembly for driving a supercharger includes a belt drive assembly for operatively connecting a gear drive assembly to an existing pinion shaft of an engine. The belt drive assembly includes a lower pulley assembly that is operatively connected to the pinion shaft and belted to an upper pulley assembly. The upper pulley assembly is operatively connected to a side gear of the gear drive assembly. The side gear engages an upper gear of the gear drive assembly, which is operatively connected to a lobe of the supercharger. Rotation of the upper gear thereby initiates rotation of the supercharger. The amount of boost provided to the supercharger is readily adjustable by simply changing the lower pulley assembly to adjust the RPM ratio for the supercharger. Each component of the belted gear assembly is isolated and fully self-contained, including a separate lubrication system and collection well.