Abstract: The positive displacement internal combustion engine has multiple stages of compression and expansion. After an initial compression, the working fluid is contained at elevated pressure and temperature. Valve controls on the initial compression can limit the thru-put of working fluid. Limiting the thru-put controls the pressure and density and as a consequence engine torque and power. A heat exchanger cools the working fluid before it enters a conventional spark ignition "combustion" cylinder. After the combustion of fuel in air in a conventional Otto or Diesel cycle the exhaust gas does further expansion in a post expansion stage. The efficiency benefits of the engine's high expansion ratio are realizable because of reductions in friction, fluid flow and heat transfer losses.