The more ethanol content in gasoline, the less powerful it is (wikipedia tells me that E85, standardized to gasoline, produces 30-35% less power). Hence, the energy density of ethanol is lower than gasoline. Basically, you need to burn more of it to get the same power, meaning more throttle and more fuel do to the same thing with E10 than E15. For that reason, E85 might be cheaper per gallon, but will be more expensive per mile. I don't think that a percentage difference of only 5 will make a huge difference, but overall, people will see slightly lower fuel economy.
The VQ37 is 11:1 comp ratio for gasoline, which is actually pretty high (few cars have a compression ratio this high, although they're more common as fuel economy is being maximized in this country; consider Mazda's SkyActiv technology, with 14:1 comp ratio). If we run E85, where octane numbers are estimated to be approximately 100 or more, we'll have less knock, which I guess someone could modify their Z's to be run on E85.
But since E15 has been approved, we're going to pay the same price for worse gas. It has less fuel and more of the cheap, rather useless ethanol. There's not nearly enough ethanol in E15 to make a difference from E10, it just means we get less actual fuel.
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"Since one of my brake light bulbs just went out, the forum told me that my piston rings are about to blow."
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