Dynamic compression is calculated by....
the static compression built into the motor and the closing point of the intake lobe on the cam. Example: 13 to 1 compression and Crane's 308 adv. duration solid cam with a closing intake point of 80 degrees gives you a dynamic compression of 8.97. For that combo you're going to need 100 plus octane. Also, if the heads are aluminum or cast iron will effect the octane requirements as well as the quench action taking place in the chamber during combustion. Give us your engine combination to ballpark the estimation.