Why so much inital timing???

mopowers said

I understand that. I'm just wondering what the calculators use. If they don't say, is it safe to assume they are using the "at the seat" IVC event?

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Most calculators use the IVC-at-the-seat, but I see 1 or 2 use 15* beyond the .050" angle on the intake closure cycle. The latter will estimate an 'effective' IVC that is 5 to 10 degrees earlier than actual IVC-at-the-seat (which is a smaller ABDC number), and will give you a higher DCR computation.