When serious engine builders "blueprint" an engine, they'll "port" or smooth off rough head castings around the intake and exhaust ports for better air flow. This makes it easier for the engine to "breathe" resulting in greater power and efficiency. Using the Porting Kit, you can perform this professional technique at home. The Porting Kit contains 80 grit abrasive rolls: 20 tapers for reaching into tight spots and 20 cylinders for flatter areas, two 4" and two 6" mandrels, and complete illustrated instructions. For best results use a high speed grinder. To remove more, try carbide burrs.