A few months ago I ordered a Holley 300-66 Intake Manifold. I am just getting around to installing it. I got it out last weekend and looked at it. The inside of the manifold has a rough (although uniform) texture to it. My original thought was that it should be as smooth and polished as possible. But before I took it to a machine shop I decided to ask some questions about. First, I emailed Holley; but I have yet to get a response from them. Next, I asked a couple of people that I know that do a lot of engine rebuilds. The first guy I talked to said that it was textured like that on purpose. His explanation was that the texture caused the air coming in to 'tumble' therefore effectively cooling the air. The other guy said that was total B.S. and that it should be polished. I don't know who to believe. Both are credible and experienced mechanics. Does anyone here have any suggestions? Thank you for any and all of your help.

 

intake runners should not be polished smooth. The little bit of turbulence helps keep the gas in suspension and off the walls.