Quote: "Pat I agree with you about the variables described. However if you look at the published cr ratio from the major automobile manufacturers designed for 87 octane fuel they all fall within half a point of 9:1."
Don't use manufacturer's published recommendations for anything but toilet paper.
Take for instance a traditional small block chevy, flat-top pistons, large-chamber smog heads, 8.5:1. You can run 87 octane all day every day. Swap to modern Vortec heads with smaller chambers, 9.5:1 compression, and still you can run 87 octane all day every day. The simple re-design of the chamber shape makes flame speeds much faster and you can use much less total ignition.
Factor in head alloy, piston configuration, EFI or carb, or any of the factors listed in patprimmer's post and the possibilities are endless. I recall reading an article about a high school shop class that built a chevy 502 with 12.5:1 compression, a 16:1 A/F ratio, and ran 87 octane with no detonation. It was all using a careful manipulation of the factors listed in patprimmer's post.
Sorry to be so vague, but there are just so many factors invovled that its hard to pinpoint. Give two builders the exact same set of parts and they will build two engines that have different detonation thresholds; cam ICL, ignition timing, quench height from the machine work involved, radiator efficiency... too much to predict