Originally Posted by AZfocus2012
This is where the MPG gains can be had. If you somewhat hypermile staying at the lower rpm's with premium the car will work well enough to see gains of 8-10%, at least that has been my experience. If you don't make attempts to short shift and stay in the lower rpm range, the gains from running premium will be negligible. I go back and forth with my driving style, but still run premium all the time.
My personal experience contradicts this finding. I've noted absolutely zero difference in terms of fuel efficiency when I try to drive reasonably in town with 87 octane vs 93 octane fuel as a result of the fuel itself. Certainly not 8-10%. Maybe not all the time, but generally when ever I was driving it manually I would especially tend to try to stay at or below 2000 rpm until 6th gear, and even with the car crawling along in 6th at 35 mph (1300 rpm or so) the car was fine.
It may well feel a touch more powerful (due to adjusting the variable camshaft timing in a more advanced/ aggressive manner), but it didn't seem to help the fuel efficiency any. The long term averages over close to 2000 miles on each fuel showed very little difference as an overall average per run.
That said I am experiementing with e10 93 octane again these last couple of tanks (blending in from 1/4th tank of e10 87) to see what the effects are in the cold, but it does cost a bit more per gallon.