Turbo Selection

[Libor]

Originally Posted by My5ABaby

I've been thinking about this... If I tune for E85 and actually get E70 in the tank, won't it just run a little rich? Also, most of today's pump gas varies in ethanol content. Presumably not 15% like E70 to E85, but it's still a variation.

I came to same conclusion. Engine tuned for E85 would run about 9% richer with E70.

Also, I have very recent study which examines effective octane number of ethanol and several blends with gasoline. What is awesome about this study is the fact, that it separates effects of evaporative cooling from true, so called effective octane, which is based purely on chemical antiknock properties of given fuel.

Simply said, ethanol-gasoline blends, even with very low octane gasoline as base, have peak chemical knock resistance at about 50% volumetric ethanol content and any more ethanol content just increases cooling effect.

This brings another phenomena, for given air temperature, lower ethanol content fuel realizes more of theoretical charge cooling effect and vica versa.

So effectively, as far as knock resistance goes, E85 is no better than E70 or E50, unless the intake temperatures are over 100°C.