Compression is a relative question isnt it. How full is the cylinder, thats what you compress. How much exhaust residual is there supplying heat that you cant control or dont know about? How much wrecking of the atomization has been done to the fuel by the time it gets there? The thing that determines compression maximum is the amount of energy that has already been transferred to the fuel before its compressed and then also the droplet size that your compressing and how fast its gassing. vaporizing fuel removes energy from the atmosphere being compressed thus enabling more compression. I've seen street fuel lowest octane available engines with 240psi cranking pressure have no detonation issues and Ive seen engines with 165psi detonate on the highest octane available and be unfixable without a rebuild of the configuration.