Originally Posted by someguy
last year around the same time i did a comparison on gas mileage, and as with this time, I tried to make sure my variables were constant...except for the station I filled up at. The results:
sunoco 94 (well duh) > shell 91 > esso 91 > sunoco 91 > petro canada 91 > olco "supreme"
of course these are not scientifically accurate or anything, but I made the effort, mainly because I was curious, but also because I was bored.
That actually doesn't make much sense, unless the motor was so highly tuned that it detonates on anything less than 94 (which would have to be a seriously aggressive map/compression ratio). The Sunoco 94 is 10% ethanol (as well as the 91 in most other stations) while the Shell 91 has none. This tells you right away that the Shell 91 will be more efficient.
And for the record, I did the same test in back to back tanks in my M3. The Shell 91 consistently averaged around 50km more per tank than Sunoco 94.