Quote: Thinking about it dynamically you would think lower lift should be tested at lower pressure because the piston is not moving very fast or forcefully compared to 1/3 to 1/2 way down the bore when the valve is open and piston speed is high. Also if the ex valve is open it is just scavenging depression causing the flow witch surely is not 36 inches.
I disagree, low lift is when it is moving the fastest during the overlap period and right after the exhaust valve closes, after that
Well, you're kind of(?) both wrong.
This graph from David Vizard's most recent porting book may help you understand what's going on w/ the in-cylinder pressures and seat / port velocities: 1. Highest is during overlap (at higher RPM, at least) due to exhaust-assisted low pressure 2. Lowest is as the intake cycle is closing; might even go in reverse as you get into reversion if the valve doesn't close soon enough 3. Peak after the overlap cycle has ended is shown around the 70-75* ATDC point where, in this particular graph, the pressure differential is bouncing around the 50" H20 mark
