Internal combustion engine with multiple independently rotating crankshafts and common output shaft

In a multi-cylinder internal combustion engine for a wheeled vehicle, said engine including conventional operational components to achieve standard four cycle operation within a single engine block, the improvement wherein said engine is divided into two power producing sub-units designated primary and secondary sub-units, said primary sub-unit including at least half the number of cylinders and adapted to operate during all powered movement of the vehicle, said secondary sub-unit being activatable optionally when additional power is needed, and when inactive receives substantially no fuel, each sub-unit having its own crankshaft and other conventional operational components, said crankshafts rotating in the same direction within a single crankcase and interconnected by a sprag clutch interactive with a single output shaft that delivers power to the wheels of the vehicle, said output shaft being a continuation of the crankshaft of said primary sub-unit.