Octane

[bobcowan]

Octane is predominantly used to control detonation. Detonation comes when the pressure or tempe is high enough to ignite the mixture before the spark plug can.

9:1 comprssion is pretty low, even at 1,000' ASL. The SBF generally can't make use of more than 35* or so of timing. Even with iron heads, the only time you might have problems is when it's really getting hot; like 220*+.

What's your cylinder pressure? Have you done a compression test? If you have a big cam you might be giving away a lot of power. 9:1 is stock engine range.