Is there a calculator to do this? How do people know how much to advance/retard a cam?

Calculating the Dynamic Compression Ratio (DCR) is a good indicator.
The only real life "testing" that can be done is to assemble the engine enough to run some cranking compression checks, then try some different cam positions, to "dial-in" the cranking pressure (psi) reading into the 160-170 psi range.
DD

Thanks Doc.

After my own testing, my default "let's try this first" value is 100 deg centerline. This will get you close to optimum on 90+% of NA 225 cams.

Lou

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