Quote:
Originally Posted by Rick360
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
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Perhaps another way of expressing the point that DV is making is that many novice head porters, and these are after all 'basics' articles, start by attacking the easy to reach bits of the port which do very little for flow until the important areas have been properly modified.
Dave