Porting the intake and exhaust on Mazda RX7 RX8 RX2 and the rest is how we improve a Rotary’s “breathing” thus increasing power and efficiency. Porting includes changing the aerodynamics, shape and surface smoothness of intake and exhaust ports, which results in changes in intake and exhaust timing; not unlike a cam change in a piston engine. The main purpose of this blog is to address questions about different kinds of porting and how they affect your street rotary engine car. Let me begin by saying bigger is not always better for “street porting”. Companies like Racing Beat offer great street port templates which I highly recommend. Basically degree of port size and configuration depends a lot on the size of intake e.g. carburetor size, throttle body size and the flow capacity of the exhaust system. To maximize all-round engine performance, volumetric efficiency must be maintained. For instance, installing a 750cfm carburetor on a stock rotary with a stock exhaust will give less overall power than a 490cfm carb., the latter being a better match for the system. Simply put, for any engine speed and load there is an optimal balance between intake size, port size and exhaust flow; things need to be matched. I remember someone building a 1st gen. RX7: large polished ports, a huge turbo, over-sized intake and a 4in exhaust system, that resulted in a car than ran only a little better than a factory Turbo II RX7. Street RX’s in my opinion give better all-around performance with conservative street porting (Racing Beat e.g.), a three inch exhaust that includes a pre-silencer, turbos not larger than T60. Maximum carburetor size should be about 600cfm. Bridgeporting or semi-bridgeporting a rotary for street may produce more peak power but overall drivability, economy are sacrificed not to mention the necessary loud exhaust which in time will become irritating. It all depends on how you plan to use your RX; do you want a “sleeper” daily driver, weekend only racer or a track machine.
Could you precisely explain the difference between street porting your engine and race porting engine. If so could you also explain how they add an extra rotor the 26B to make the quad rotor.
Sorry for the late response Trentc, The degree and type of porting is the difference between street and race. The big deal in extending (adding more Rotors) Rotary engines is how to make the eccentric shaft longer and how supporting bearings and stationary gears are constructed.