This invention relates to the field of internal combustion engines and compressors in general and to linear compressors, in particular these used as in U.S. Pat. No. 8,056,527, by accurately controlling the pressure being delivered into the combustion chambers of said engine while returning unused energy of the compression phase into the motor for complete expansion.Another improvement relates to a pressure compensated vane to be used inside grooves of the motor assembly rotor. This invention enables the vane to seal against the cavity of the housing tightly with minimal force.