Let's see if I've got this right.....the reason that most people get better gas milage with 89 or 87 octane is that the car's computer adjusts for the lower octane gas and by doing so lessens the performance of the car. So you end up with a trade off; better milage but less performance. I know this is probably an over-simplification but can anyone explain it better than this? Then my next question is, is the drop in performance small enough to justifiy saving the 5-10 cents per gallon difference in the price between mid-grade and premium?

 

last weekend I took a trip...

Going to the beach I got 22.1mpg with Sonoco 94 octane. Going back in similar driving conditions I got 25.4mpg with Exxon 89 octane. There is no way I'm ever using premium octane again

 

how fast were you going? Wind direction? road condition? everything was the exact same way ?

 

ummm...

a) between 65-75mph depending on the speed limit... actually on the ride home I did 30 miles at 85mph because traffic was going quite quickly
b) relative to the car, the wind was going 65-75mpg the other way
c) drove on the same roads
d) well because of the curvature of the earth I guess going north on my way home was more downhill then going south

 

pretty funny ! i just got back from a trip from Mtl to the coast of Maine and back. I drove at about 65 mph average on my way down, took a smaller road through NH and at about 85 mph average on my way back. mixed up a bit of 89 and 91 octane gaz all the way and managed close to 23 mph , my best ever. I had just the day before my car reflash to the M version. Maybe it helped...