Abstract: The specification discloses a rotary gas pressure engine system including a housing and a stationary shaft extending through the housing. A circular cylinder block is rotatably mounted on the stationary shaft. The cylinder block includes a plurality of radial piston cylinders and a piston mounted within each cylinder for slidable movement therein. The cylinder block further includes a circumferentially mounted cam ring having generally elliptical risers around its inner periphery in order to cause radial operation of the pistons. A vane pump is associated with the cylinder block for pumping fluid from a fluid reservoir external of the housing and through the housing to a vaporization chamber external of the housing.