Which fuel do YOU use

[severous01]

ethanol burns at a 50% less ratio than gasoline. but, it will not detonate in the chamber. so, you're only 95% efficient running any gasoline other than 100% in the US.

second...the rating of octane is not how efficient it is but the burn rate or detonation prevention of the gasoline being used. 87 octane is 87% less likely to detonate at a specific compression than 91 octane which is 91% less likely to detonate. 91 octane burns slower allowing for higher compression or more advanced spark....hence the higher octane rating of performance cars and such. it has NOTHING to do with fuel economy...and actually 93 octane is cheaper to produce than 87.