fuel prices going thru the roof again

[Darlo]

The most they put in (In Canada) is 10%, and as far as I know, ethanol burns with 60% the output.

So you have 90% reg gas burning at 100% = 90%
Then you have 10% (eth) burning a 60% = 6%

This still gives you a total of 96% output, which means that you would only see an increase of 4.167 (100/96 - 1) if you were to run with no ethanol.

Now keep in mind this is power per volume (aka gas mileage)

[Pu241]

Click it, Darlo is correct in his calculations as BTU's are concerned.
But, I run 89 because I see about a 3 MPG difference in my MPG vs 87.
I agree with him in regards to the 91+ octane being as waste, unless you have maxed out the advance on the distributor, and even then I would question if you'd be able to take full advantage of the octane.
Darlo, also is in a unique position, as he has previously stated, that he rarely exceeds 50 MPH, which put him in the sweet spot for the 1.3 engine and he truly may not see any increase in MPG with higher octane fuel.
Much depends on your driving habits and driving environment.

[Darlo]

I did try buying 91 oct for a couple fills and did see an increase of about 1mpg (maybe 2), but the cost difference didnt make it worth it for me. (which is basically what you said)

[Pu241]

I did try buying 91 oct for a couple fills and did see an increase of about 1mpg (maybe 2), but the cost difference didnt make it worth it for me. (which is basically what you said)

If it wasn't for the 2-3 MPG increase the 87/89 price differential wouldn't be worth it for me either. Although I feel it sounds better when its running on 89 vs 87, that's subjective and prone to interpretation, were as the MPG increase is measurable and is documented. I do wonder if I didn't have to run 60 MPH, and more occasionally, if I might not be able to get by with the lower octane! Real gas would also net both of use a little more MPG, but that's not likely to be back anytime soon.