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Originally Posted by DavidVizard-GFN
it appears that the point of greatest flow restriction is at the valve seat. This is actually the case
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I've done some flow testing where I
removed the valve and the flow did not increase. Usually this was on heads that had a fairly small (relative to valve throat) pushrod pinch. I bet the section of just the valve and seat would flow very good with the valve opened more. Most flow enters the cylinder when the valve is much more than 1/2 lift when the piston is moving fastest, why use such a low lift. Flow at low lifts may be important on street engines or restricted cam engines, but flow at low lift is a detriment in a serious racing engine IMO.
I agree that the valve seat is an important part of the port as is the short turn, but this test means very little at such a low lift. I think it is quite obvious the valve is the restriction when the valve is partly open. The valve would have to be open to ~ .23 L/d (~.480" on a 2.05 valve) to have the actual valve curtain area larger than the valve throat at 90%.
Rick