It is my understanding that optimum design dynamic compression ratio for 91 octane is from 7.5 to 8.5 with the sweet spot at 8.2:1.

What is the optimum dynamic compression ratio for 87 octane?

There are so many factors that go into this.
I am running 91 with a 9.5 ratio with no problems at all.

Here are all the calculations you may need http://www.smokemup.com/auto_math/index.php

have to subscribe for the advanced stuff

Good info http://e30m3performance.com/myths/mo...comp_ratio.htm

and here
http://www.popularhotrodding.com/tec...on_ratio_tech/

there is no single answer. the fuel you can get away with is directly and specifically related to the ability of the combustion chamber to not develop hot spots that cause detonation. the ability to do that is a combination of the design of the cumbustion chamber itself as well as about 500 other variables... an 8 : 1 motor w/ a bad piston shape and cumbustion chamber will eat itself on 91 and a 10 :1 with a proper shape and design will live just fine...

there is NO single magic bean answer. it is all combination and design. for example.... most of the good bike motors are running 11.5 to 1 on pump gas... and i THINK the new kawasaki is higher than that... how do they do that ? easy... they know what they are doing.

a properly configured 9.4 :1 motor should run 91 all day... IF thats really what you are buying and IF the rest of the motor is configured properly.... a significant mistake in any one area , renders all your and calculations assumptions meaningless .

All are excellent resources. Thanks. The last article answered my question, not with CR but with combustion chamber psi numbers versus octane. Based on that information I feel that I am where I need to be for 87 octane I run. Thanks again to you and everyone else that provided input.