Porting and Polishing

I posted a video on YouTube awhile back about porting and polishing cylinder heads. I had many comments, mostly positive, but there were a couple that claimed polishing the head that much was not good and roughness was needed to create turbulent flow. While that may be true for a naturally aspirated engine, the engine for my Cobra is fuel injected. The only thing going through the intake will be air that will mix with fuel vapor right at the injector and dump right into the cylinder. The picture above is of a freshly machined cylinder head for a 2012 engine. As you can see the runners are very smooth because most engine parts are precision sand cast. Old sand casting for cast iron left very porous surfaces that allowed carbon and other contaminants to build up. New castings are very fine. Precision sand casting and lost foam technologies produce an intake runner that is very close to a final port and polish job. Laminar air flow is more efficient and is being used more and more on newer engine designs. Combined with direct injection, these new manufacturing processes are what give smaller engines more horsepower and better economy.