as im seeing a lot of info here that seems misleading to my knowledge i would like share my 2 cents on this..
octane = higher octane is less likely to prematurely combust under pressure than lower octane.
to my knowledge adding oil to the fuel acts more as a octane booster than a reduction since it has a higher flame point than the gasoline itself.
higher octane fuel will combust at a higher temperature and require higher compression to be used effectivly.
the reason higher octane helps some vehicles and not others is simply a matter of compression and engine design itself
a high octane fuel will explode more slowly in a low compression engine because the compression was not causing enough pressure to cause the fuel to almost spontaniously combust.
the fuel explodes in the cyl more eaisly when the fuel is closest to spontanious combustion but not actually reaching the point of it.
with too high of an octane the fuel will explode too slowly when the engine has too low of a compression to put the fuel near its spontanious combustion point. when this happens the fuel explodes with less energy. and a good portion sometimes even goes unburned/partially burned and creates buildup (the above condition also causes loss of power and higher exhaust temperatures due to fuel still being lit as the exhaust port opens in extreme cases)
with too low of an octane you will hear Ping this is because the fuel combusted before the spark plug even fired or because the fuel exploded so rapidly compared to what it was designed for/timed at.
the ping sound is actually the sound of the explosion happening before the piston reaches the top of its stroke (TDC) it actually trys to force the piston to go back down but in reverse, because the crank isnt past the top dead center.
But because the engine has so much centrifigul force already moving while running this causes the top of the piston to take extreme forces and the crank as well because it actually has to compress the explosion instead of using the explosion to move you. ping can blow holes directly through pistons just from the shockwave alone of trying to compress an explosion.
its hard to explain these things so i can understand why there is confusion on this subject.
if anyone has any corrections to my statements feel free i would rather be wrong and know it than be wrong and never learn.