Porting and Polishing Explained: What It Does and If You Need It
Porting and polishing are modifications that are done on the intake and exhaust ports on an engine’s cylinder head or intake/exhaust tracts. Porting and polishing maximizes airflow to bring more power to the engine and adds up to 4 horsepower. Porting reshapes and enlarges the ports to improve airflow efficiency. Polishing smooths out the inside of the cylinder, reducing air resistance. Porting is more complex in 2-strokes because the ports are built into the cylinder and control the timing of fuel/air entry and exhaust exit. In a 2-stroke, the piston itself controls when the ports open and close. Thus, any change to the port affects when fuel/air enters, how long it stays in the cylinder, and when the exhaust leaves. Even the smallest changes in porting can drastically alter the powerband, engine responsiveness, and peak RPM. Because of these factors, precision is key when porting and polishing 2 strokes. The typical 2-stroke engine has 1 or 2 exhaust ports, multiple transfer ports, and one intake port. Each one of these must be precisely shaped, timed perfectly, and symmetrical in flow. If it is incorrectly ported and polished, then it can cause the dirtbike to lose power, or it can damage the parts. 4-strokes are slightly easier to port and polish because it does not affect the timing like a 2-stroke engine. The timing of when the intake and exhaust open and close is controlled by cams and valves, which are separate from the ports themselves. The ports in the cylinder are fixed to guide airflow, but do not open or close like in a 2-stroke engine.
