Abstract: An integrated speed changer assembly for increasing or decreasing the rotational speed of the output of an engine, or other prime mover, to that required by the input of a process machine. The assembly includes a housing, a flywheel assembly, an internal ring gear and a pinion. The housing has a shaft opening and a flywheel opening. The flywheel assembly is coupled to the crankshaft of an engine and positioned to substantially cover the flywheel opening of the housing. In an integrated speed increaser embodiment, the internal ring gear is coupled to the flywheel assembly and has ring gear teeth on its inner surface and is positioned concentric with the flywheel assembly for rotation therewith. The pinion has a driven shaft that extends axially and which projects through the shaft opening of the housing. The pinion has pinion gear teeth on its outer surface which are suited for meshing engagement with the ring gear teeth of the internal ring gear.