Attached is the spreadsheet zipped up for download. This uses the angle and width of the seat, top cut angle and widths and the valve face angle,width and backcut angle and width.
This pic shows pretty well why the actual curtain area is really less than normally calculated area. The one F1Fever posted uses the seat angle and width to calculate the inner diameter of the valve seat and calculates curtain area there but is still considerably larger than the real curtain area.
Using a 2.08 valve with 50º seat .060" wide shows area of .62"@ 0.100" lift on the one F1Fever posted. My spreadsheet shows .426" @ 0.100". The old standard formula (VlvDiam x PI x lift) = .653". You can see how far off these are in reality. Specs for VJ = 43º-.100",50ºseat .060" : valve backcut 35-.070"wide and 12º valve back angle.
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Lift Old Formula My Formula
.100" .653sqin .426sqin
.300" 1.960sqin 1.461sqin
.600" 3.920sqin 3.258
This is directly related to the low-lift flow thread in the advanced section from a couple weeks ago.
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