Your Yamaha engine has been designed
to use regular unleaded gasoline
with a pump octane number
[(R+M)/2] of 86 or higher, or a research
octane number of 91 or higher.
R is for the Research Octane rating.
M is for the Motor Octane rating.
These are two methods of measuring octane. What's on the pump is usually (R+M)/2 which is the average of the two.
Octane is just resistance to detonation. Higher octane fuels have more xylene or toluene in them, both of which have extremely high octane ratings (117 and 114 if I remember right).
(As a sidenote, I tested out a gallon of xylene mixed into four gallons of 89 octane gas. The result performed like premium in my turbo bike, which does normally detonate on 89 octane fuel. I never tried a gallon into 91 or 93 octane, but the results would have been fun.)
Due to this detonation resistance, you can advance the timing, or increase the engine's compression ratio, or add a blower (another way to increase compression ratio) and not have the engine detonate.
The thing is, lower octane fuel actually produces more heat than high octane, which means more energy. So if you haven't got a knock sensor, racing engine or blower, the lower octane fuel can make more power than the premium stuff. The only way the high octane fuel makes more power is if you retune to take advantage of it.
Fred
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