Ok yall,
I have found it to be generally agreed that a cranking pressure under 180psi will keep you on pump gas. There is a very good article in “Hot Rod” Aug 2005 on all of these issues which continues to back up all of the data.
With modern high swirl closed chamber heads with a tight quench you can easily approach 200 psi or a little above and still run on pump gas if everything else is dialed in. With coatings and polishing of the chambers over 200 psi is not an issue.
I have a 360 with magnum heads that that has a tight 0.039" quench, has between 180-190 psi cranking pressure and a static compression ratio of 10.6:1. No special coatings on the pistons and no polishing of the chambers and I run the engine on 89 octane and can use 87 in a pinch if I am careful how I drive.
The particulars of the actual design of the engine has as much to do with octane requirements as anything.
