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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I would think so. That will always give the best and most accurate result. IVC can be a lot different on two different cams from seat to .050. They might have the same at .050 but be different at seat. Depending on lobe shape, style, ramp rates, roller vs flat, etc etc. The cylinder starts building pressure at seat, not .050, so that's the best. Personally I use:

Wallace Racing: Dynamic Compression Ratio Calculator

And it even mentions at the top, use seat value.