compression ratio to cylinder psi

if you knew when the intake valve closed couldnt you reverse calculate your way into a close guestimate? just thinking out loud here

Nope. How is that going to tell piston head volume, combustion chamber volume, deck clearance and a myriad of other variables? The only way for sure to be accurate with an unknown combination is to disassemble and measure. If it has strong cylinder pressure, that just means it's in good shape and a good combination. That's no indicator of static compression ratio whatsoever.