Which Intake manifold gasket

furrystump said

I’m just discussing the transition from intake to head. Not the runner size/shape etc. It is my understanding you never want the flow to impact a right angle surface. So an intake port ever so slightly smaller than the head port is the better way to go. It also helps with reversion because those pulses hit the right angle as the flow tries to reverse up the intake tract. Perfect being exactly the same.

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No, you need to think in terms of air flow (fluid really) and what it does when it encounters transitional changes.

If you make the port in the manifold smaller that the port in head you WILL induce turbulence right there as the air will try and get to the low pressure area made by that mismatch. You NEVER want to induce turbulence or swirl or any of that junk in a port, and that’s exactly what you are doing. Air is always looking for low pressure areas to get to, and that mismatch does just that.

If the manifold is bigger than the head, the air will pull away from the mismatch and form its own smooth transition. It’s not optimal, but it’s better than the other way around.

It is 100% a power killer and it makes tuning a PITA.

And I’m not sure how you look at a port and isolate out one part. It is a system. In fact, the valve job has a direct influence on the carb and how it behaves. So you can’t take a part out of the system and isolate it.

You never want the port in the manifold smaller than the port in the head. Ever. And if matching the ports makes an hourglass shape don’t do that. Better of leaving it alone.