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Bingo, the porting stone pattern trips the boundary layer into a turbulent layer, allowing larger scale patterns to develop, the 'swirl'. It's the tripping of the boundary layer to turbulent that allows the increase in air speed. As an aside, the opposite occurs in boats. Racers used to wax the hull to allow water to bead up. It actually takes more energy to force the water to bead up than it does to allow it to 'wet' out against the hull. Racers use a smooth, but not waxed surface now. They want to encourage a smooth transition between moving hull and stationary water, it's more efficient. Jeff '67 Sqbk * * * * * * * * * * * * Oh boy, finally a topic I can offer my two cents. Polishing the intake manifold, does offer an advantage, over a non-polished manifold. I'm not sure, if you would see any gains with a stock engine. Once we port and polished the heads, the manifolds had become a restriction. And you must match port the manifold with the head (gasket included). We've also found out that, if the manifold gasket projects just the slightest amount into the port, flow is reduced. Today polishing the manifold thinking has changed. We port the manifolds, but don't polish them, like we used to. The porting stone leaves a fine pattern, that improves flow by creating a swirl pattern in the air. This also increases the air speed. Hopes this helps you.