CNC Mill Mark Removal in Intake Port

Syleng1 said

So with multi port fuel injection and the injector just above the valve… there is no time for fuel atomization at high rpm. And anyone who wants to tell me the length of the runner and head port is enough at 4,000rpm to “mix” and properly atomize fuel and air… I don’t buy it. Will rough runners help? maybe, but explain sheet metal intakes? Manufactures trying to get more fuel miles from a gallon of gasoline do not polish or touch intakes - at all. If there were value they would.

SN: great work by Early A. I appreciate the energy.

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Here's my understanding from some Darin Morgan videos: Intake manifold for dry flow in a MPFI system would be smooth. Downstream of the injectors needs to be rough, 60 grit or rougher. The interesting thing is that upstream of the injectors (for some distance I can't remember) needs to be rough as well. This is because flow is not always in one direction.

For wet flow intake manifolds and runners, 36 grit. For heads, 60 grit or rougher. As velocity goes up, surfaces can be smoother. Since intake manifolds/runners are usually lower velocity than head ports, go with rougher texture.