Flow Data from Intake Valve Relocation

Earlie A said

I have never flown a port backwards. I’m not saying you are wrong, but I heard Darin Morgan say to fight reversion with velocity and cam timing, not seat angles. I do know this. The steeper top cuts fight reversion both on overlap and the short side reversion that occurs at high intake valve lift.

Seat is 0.050 wide. 65 cut is 0.110. Width of 75 degree cut varies as can be seen with the purple line length. As you can imagine, the undercuts hit much harder on the exhaust valve side than on the cyl wall side. I like the way this leads the air into the combustion chamber.

All cutters are Goodson 3D system. Angles are individual cutters since all this is experimental. It’s just easier that way. I did make a custom cutter for the top cut that is a 40 degree that transitions to a 90 degree with a 4mm radius. This cuts the 40 degree all the way out to the 90 degree at the 4.07 bore circle in one cut.

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That’s why following one man’s opinions as gospel is bad policy.

Larry Meaux says he flows his heads backwards. How do you know what the port will be like for reversion if you don’t flow the port backwards?

I’ve seen heads that flowed big numbers and they didn’t make power. I flowed them backwards and guess what? It flowed about 85% in reverse. That’s pretty high.

Once you see that you can fix it. And of course we aren’t working with the same heads he is. There is only so much you can do with the ports you are working on.

Just about anything that stops reverse flow even if it hurts forward flow will make more power.

If you don’t flow the port backwards how do you know?

Same with the exhaust. Some Chevy ports will flow in both directions at the same time. That hurts power.

Curtiss Boggs just did an interview and most of what he said aligns with my testing and not the orthodoxy I’ve heard for 40 plus years.