Originally Posted by BetaDnB
Here's what it says on page 351 RE fuel ethanol/E85
During the summer season, fuel ethanol may contain a maximum of 85%
denatured ethanol (Ed85) and 15% unleaded gasoline. The fuel ethanol
has a higher octane rating than unleaded regular or premium gasoline
and this allows the design of engines with greater efficiency and power.
This basically says higher octane = greater efficiency and power.
Pg 351 is talking about flex fuel vehicles which i don't believe the 12 Focus is yet (mine isn't) so you can't even use E85. Typically flex fuel vehicles get about 25% less mileage compared to running it on gasoline and make less power too.
Yes, an engine designed to run on just E85 can have very high compression allowing it to make more power but because E85 has less energy content than gasoline will always use more. But a flex fuel vehicle is designed to run on both gasoline and E85 so it can't be designed to take advantage of the 100+ octane rating of E85, still needs to run on 87 octane gasoline.
So, "higher octane = greater efficiency and power." is wrong when it comes to the Focus.
My comment was in response to the first paragraph under "Octane recommendations" on pg 354. Where the sentence; "Premium fuel will provide improved performance." You can't take that out of context from the rest of the paragraph.