after top dead center and lets off the rotor at approximately 30 degrees after top dead center the gate 250 bifurcates the expansion chamber when it contacts the rotor whereby it prevents pressure from acting on the rotor behind the gate bifurcation or splitting of the expansion chamber into two parts is accomplished since the rotor faces are undished so that the gates can engage the rotor an alternative gate 450 is illustrated in fig1 22 and 23 gate 450 has ends 451 and 452 gate 450 can be a flat piece of spring steel that bends or pivots the gate is biased to be flat but can be bent or pivoted to contact the rotor 60 in this embodiment a slot or slit can form the opening in the radius and the gate 450 can be press fit or adhesively held within the opening it is appreciated that the gate 450 projects from the housing wall in a slanted manner toward the adjacent inlet and away from the adjacent outlet gate 460 can be provided and is similar to gate 450 it is understood that the portions of the gates within the housing are movable it is preferred that the gates are movable from a first gate position wherein the gate is flush with the housing wall to other positions wherein the gate either contacts the rotor or is projected into an expansion chamber without contacting the rotor the gates preferably are operable to rotate in the same direction as the rotor this allows pressure to press the gates against the rotor as well as allowing the rotor to slide over the.