Rotary Engine Porting

Port Terminology

Peripheral ports are the exhaust ports located in the rotor housing, while the side ports are located in the side housings on either side of each rotor section. The side ports are for intake, the peripheral ports are for exhaust.  For reasons that will become apparent, common street engines produced by Mazda have side intake and peripheral exhaust ports. This typical setup allows minimal overlap and better control of intake timing, and also permits very free exhaust flow. The side intake ports are triangular in shape.

There is no universal terminology so bear with me. The outside edge is the leading side of the port as it determines when the port opens. The top edge is the trailing side of the port as it determines when the port closes. And the remaining side we’ll refer to as the inside edge. Further, the port has three corners, which we shall call the tail (pointing down), the nose (facing inside), and the shoulder (connecting the leading and trailing sides).

By altering the location and shape of these elements we are able change port variables. In general, moving the leading edge out advances the opening timing and increase overlap, and moving the trailing edge up extends the port closing. Changing the angle of the port edge (scissoring) or its curvature (rounding), with respect to the rotor face, alters the rate of opening or closing, which affects motor’s torque characteristics.

Gradual opening and closing of ports promotes a broader power band, where as one that opens and closes rapidly has higher peak power. The corners are where you can alter lift without affecting port timing.