A four stroke internal combustion engine having a flexible arrangement is disclosed such that the engine can be easily configured for supercharged or normally aspirated operation. The engine includes a cooling system that includes both closed loop and open loop cooling systems for improved cooling efficiency. A power take off housing located on one end of the crankcase. Various engine components are operatively coupled to the crankshaft within the power take off housing including a cam shaft for a valve actuation assembly, a generator, an engine starting mechanism, a balance shaft, and a supercharger. The engine contemplated in accordance with the present invention also includes a dry sump lubrication system having lubricant separator for separating lubricant from blow-by gas within the engine.