CR numbers we use everyday is the static CR, it’s only a reference number determined by the parts we use, dome, stroke, volume etc. dynamic CR (running CR) is determined by those same parts but adding in the number of degrees past BDC when the intake valve shuts and the cylinder starts making compression. The dynamic CR is what requires different levels of octane. The bigger the cam or the more valve timing overlap will reduce dynamic CR while the static CR remains the same. As you increase overlap you can increase static CR, in fact you should increase the static number or if you add too much overlap you will drop the dynamic CR too much and not make good power because you turned your engine into a low compression engine even though you didn’t change the static number. Yes I know I get long winded. Lol