Pe,

I agree, but in this country we don't have any control over fuel quality or purity (which is all over the scale) so unless you want to buy some extremely expensive racing fuel octane ratings are a good general guide. Over here you never know what the EPA additive of the week will be. Most of the U.S. made and Chinese engines have lower compression ratios than those from Europe. Here in the U.S. using "premium" gas with octane ratings above 90 seem to work out ok for the European engines and using "regular unleaded" with octane ratings of 87 and above work out well for the rest. When it gets hot outside, say above 100f, the lower compression engines benefit from the use of premium fuel where the European engines need closer to 100 octane (our measure) to prevent pre-ignition. Which is why I said "generally".

VPL racing fuels are where most would have to go here for better octane ratings and vapor pressures. Expensive without even looking at HazMat shipping!! Avgas has so much lead in it that the stuff is more trouble than it's worth.

At least on this side of the water vapor pressure and flash points go a bit beyond what the average modeler is ever going to care about.