How to Increase Low End Torque by Porting Headsby Robert Bayly
Porting cylinder heads generally refers to the process of enlarging the intake and exhaust ports of an engines cylinder heads. Porting is usually done to increase airflow and horsepower at high RPM. Heads with smaller ports – un-ported – usually provide better low-end torque than ported heads. Still, there are some porting procedures that can be performed, without significantly enlarging the ports, that will result in better low-end torque.
Remove the rough casting surface of the intake ports with a tapered medium grit stone from a head porting kit, mounted in a Dumore flexible shaft grinder. Remove just enough material to remove the rough surface and leave a swirling pattern in the port.
Repeat this process with a fine sandpaper bit. Leave the marks the sandpaper makes in the port. Move the bit so the marks point into the port at about a 45-degree angle relative to the entrance of the port. This will prevent fuel pooling in the ports and impart a “swirl” effect in the incoming fuel charge.
Remove the rough casting marks in the exhaust port with a medium stone, using the Dumore flexible shaft grinder setup. Move to a fine stone. Remove as little material as possible. Polish the exhaust port with a felt wheel, mounted in the Dumore setup. Use jewelers rouge, starting with coarse – black – and moving to red, brown, and finishing with white. This will polish the port to a shiny, almost mirror finish. This will actually aid in the movement of exhaust gasses.
Place an old set of valves in the cylinder head. This is to protect the valve seats. Place masking tape on the surface of the cylinder head. Trim the tape with a razor blade so only the chambers are exposed. Use the Dumore flexible shaft grinder setup, felt wheel and rouge, to polish the combustion chamber. This will enhance combustion and prevent carbon buildup in the chamber.
- It would be a good idea to practice this on a junk cylinder head so you can get a feel for it. Remember, remove as little material as possible. Porting is an art.
- A bad porting job can actually decrease performance. If you are unsure about doing this, take the heads to a professional.