On our Pontiac heads or any head that has a push rod pinch point area reduction, that area does not become a restriction until the port area after it ( down stream from the pinch point) is saturated with air flow, unlike other parts of the Intake port.
This is because the push rod pinch is a mostly straight lenght of runner .
This ties in with the other cut in stone rule about high speed air, that being with anything sharper then a 15 degree change in flow path a large high speed air mass will just sheer way staying on the path of least restriction.
Also you just can't A/B our Pontiac heads in regards to the push rod pinch area with a SBC because our post 67 heads have a 14 degree valve inclination angle and the SBC has a 23 degree.
This factor greatly changes how much of a restriction the push rod pinch is from the bottom to top of the runner.
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I do stuff for reasons.
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