Originally Posted By: Kawiguy454
Originally Posted By: 440Magnum
Originally Posted By: MNgopher
. The non-oxy delivered better fuel mileage (as expected), but it appears it does not unlock better performance at the same time.
Absolutely no surprise there. Non-oxygenated fuels have a higher energy density, so miles/gallon is generally better.
Alcohol is a tremendously effective octane booster, so although it has low energy density requiring more to be injected on each cylinder firing, it delivers more power because the engine can set the timing with less regard for detonation. The most extreme example is a flex-fuel vehicle like my Ram. Mileage drops like a rock on E-85 (from ~16 in regular commuting to roughly 12 under the same conditions), but power and throttle response are both better because E85 is far higher octane than even E0 premium.
I think your idea of why alcohol makes more power is incorrect. 91 alcohol blend and 91 pure gas have the same octane/knock resistance so the ECU will use the same timing control settings. The reason alcohol makes more power especially on turbo applications is due to its cooling effect on incoming air charge as it is atomized.
Mayyyybeee.... alcohols have about 1.5x the latent heat of vaporization of hydrocarbons like kerosene and gasoline. I don't think that's enough to significantly change the "cooling effect" (which is entirely due to heat of vaporization) when it only accounts for 10% of the blend. The only thing that has a truly significant cooling effect on the incoming charge is water injection, since water has a much greater latent heat of vaporization than either alcohol (3x) or gasoline (4-5x), and also doesn't add heat to the combustion chamber by burning. Its an inert heat-buffer.
The octane ratings posted on the pump are a *minimum*. I think the E10 blends tend to over-shoot and have a higher real-world octane rating than the E0 blends, since its so much harder to boost the octane without ethanol now that MTBE is no longer available. When alcohol can be part of the blend, its a lot easier to bump the octane up without adding a lot of cost to the final product, so there's less motivation to hit the bare minimum requirement.