Abstract: A piston compression system converts energy from a conventional combustion cycle engine driving a piston to displace a working gas for flow through a turbine for output power. The working gas is derived by diverting a portion of the charge during combustion at near peak combustion pressure (PCP) into a closed working volume. The working gas is maintained at high pressure within the working volume. The working volume has a first displacement compartment and a second displacement compartment, a supply manifold connected for receiving pressurized working gas alternately from the first and second compartments and connected to an inlet of the turbine, and a return manifold connected to an outlet of the turbine and alternately returning working gas to the second and first compartments.