Are there advantages to staying with small valves? What about polishing the ports?
There are many reasons to keep both intake and exhaust ports small. On the intake side, small ports with rough surfaces are more efficient. They increase the velocity and enhance the atomization of the air/fuel mixture for a more complete burn during the combustion cycle. While it may take more labor and skill to make a small port perform at peak efficiency, small ports of the correct shape can equal the CFMs of an inefficiently designed, large, hogged-out port. On the exhaust side, small ports are also more efficient in increasing velocity. However, these ports should be polished smooth rather than being left rough, to increase the scavenging flow of exhaust gases. In addition to flowing more CFMs, polished exhaust ports transfer less heat to the heads which helps prevent engine-damaging detonation.
