Abstract: An internal combustion engine is provided having pairs of separately designated combustion and exhaust cylinders for implementing a two-stage exhaust system which derives work from the combustion gases of the combustion cylinders. The piston within each exhaust cylinder is timed by the engine's crankshaft to lead its corresponding combustion cylinder's piston by roughly a 30 to 90 degree crankshaft angle. Ignition of a combustible fuel mixture within the combustion cylinder produces combustion gases. The expansion of the combustion gases drives the combustion piston during a power stroke, and are expelled from the combustion cylinder during an exhaust stroke. The combustion gases exit the combustion cylinder via a fluidic passage to the exhaust cylinder. The combustion gases are received by the exhaust cylinder at the start of its piston's intake stroke. The timing between the combustion and exhaust piston is such that the combustion gases exert a force upon the exhaust piston during its intake stroke.