The rule of thumb for naturally aspirated stockish cam compression I've always heard is move the decimal point to the right for the octane.
9:1=91 octane
10:1=100 octane
Heard this would allow max spark advance in most motors.
Dunno how correct, but that's what I heard.
Most blower motors run lower compression, not higher.
That's a terrible rule of thumb, and there are tons of 10:1 engines running around on 93-94 pump gas w/o any issues. There is no "rule of thumb" because the amount of
variables that affect suitability are nearly endless. From head and block materials,design,cooling system quality & effectiveness, spark plug location & cooling, quench vs.
no quench vs squish vs the terrible zone in between, piston design, intake system fuel distribution variation,....................it doesn't end there but You get the idea.
