CNC Mill Mark Removal in Intake Port

Earlie A said

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.

Click to expand...

If you can (or if you even care to do it) go to Drag Boss Garage on YouTube and look through is Darin Morgan videos.

I can’t remember which one it was but the topic came up.

In that video he said for a wet (carb) intake it should have a rough finish everywhere. If it was injected you use a rough finish 3 inches above the injector to the manifold face.

Chad Spierer only does a burr finish on his intakes. And on some of his ports.

Larry Meaux was interviewed about 20 years ago. I’ve posted the link to it many times. He says he is doing a burr finish everywhere. The rougher the better. That’s the intake manifold, the intake port, chamber and exhaust port.

And he said he found power doing it every time.

What I found was when the step over got big enough the port would go so turbulent you couldn’t read the manometer.

When I was testing burr finishes I never could get it rough enough to duplicate that. And for the most part the burr marks run parallel to the port where the step over runs perpendicular.