I think the whole octane thing is pretty strait forward on the high compression engines 12.5 + but on the mid compression rigs 180 to 210 psi cyl pressure it gets tricky, too much octane leads to a lot of spark advance and the possibility of negative work, too little octane eats engines, I wish the 103 octane fuel was available here but haven't found it yet so the 100LL seems to fit the bill for my engine, I have run the best ETs on 93 and 110 race mix but cant seen to get a consistent mix