[hightower99]

Originally Posted by revetec

A good finish on an intake port is a slightly rough to feel finish that is not wavy. I have heard that bead blasting an intake port is the best because it creates small vortices that create a kind of an air ball bearing effect from the port to the intake charge. I'm trying to find more information on this.

A good finish is a relatively uniform roughness. The reason is because on the intake side you want to diminish the slow moving boundary layer to help keep the fuel airbourne (by making the boundary layer turbulent). For the exhaust ports and manifold you can actually get better performance (not necessarily more flow) by polishing the ports smooth because for the exhaust you should be more concerned with maintaining laminar flow. I would think that a uniform, one-way pattern would get the best performance through the intake manifold and ports. I always think of shark skin.

Originally Posted by revetec

One thing I can quote is the porting article on Wikipedia which states, "Flow bench testing shows that the difference between a mirror finished port and a rough textured port is typically less than 1%".

Yes and this is important for 2 reasons. One, getting your ports polished is expensive and it will only net roughly 1% more flow and two, polishing increases the boundary layer and you will end up having fueling problems and probably combustion problems as well.

Originally Posted by revetec

One thing that can be said is that when porting a head, it is easier to see the variations of port surface when polished. After you have completed a port and slight polish and inspect, a good practice would be then to rough up slightly the surface or bead blast the port. But then again it is stated as a 1% variation in performance between the two.

It stated a 1% difference in flow. Engine performance will be much more than 1% between and engine with smooth polished intake manifold and ports and the engine with uniform, one-way roughed manifold and ports.