Question on port matching

rumblefish360 said

Sorry man, your just confusing me. I feel like your flipping back and forth. You said you said it before, I must have missed it. Now your saying none but earlier you were saying there has to be some because of the gain you say when there is with a larger port intake on a smaller head port.

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Show me where I said to, on purpose make the manifold bigger than the head? This all got wonky because I told the OP to NOT port match his stuff. And this is exactly why.

It’s not what it really looks like. Changes in section are a big deal. In most cases, you want some taper in the port, from the carb flange to the valve seat. If you port match and don’t account for that and literally put a bulge in the port at the flange it will lose power. Every time.

Go back and look at the first video I posted. Watch what happens when the flow goes past the square edge. The flow tries to fill in behind that square edge and vortices happen. Increasing flow speed only makes it worse. That video makes it very clear.

One more time. IF and only IF you have to have a mismatch at the flange, make the manifold bigger than the head. Not the other way around.

Don’t get hung up on which will flow more air, which one will keep the fuel suspended in the air or anything else. It’s about not disrupting the flow AFTER the mismatch. The smaller intake port will cause unwanted turbulence AFTER the mismatch, the bigger intake port will not.