How much does ethanol gas effect your tunes?

[COBESGT]

So I took the Mustang on a 450 mile trip yesterday and the place that stopped for gas only had ethanol gas, 89, 91, and 93 octane. I always run 91 non-ethanol gas in my car as I have the 91 octane tune. To be safe I used the 93 octane, figuring if the ethanol did any strange things I'd still have 2 points to spare and I'd still be safe. So, does anyone have any ideas of how ethanol effects tunes?

 

[jpplaw]

Chandler at Brenspeed told me once that their tunes normally take the 10% ethanol fuel into account. I have also heard that ethanol lowers octane and leans out the mixture. I used to race at a track that had a supermodified class and they ran super-rich on methanol.

Not sure if the octane numbers on the gas pumps are pre or post ethanol addition though.

 

[DarkFireGT]

Doesn't change it enough to harm it. And Brenspeed, being in the heartland, definitely takes that into consideration. You do not need to run a higher octane. The difference in MPG is also usually less than 1 MPG.

 

[ski]

Pure ethanol has an octane rating of 113, and less BTU/gallon than pure gasoline. E10(10% ethanol) fuel has the octane rating that's posted at the pump. E10 fuel reduces mpg.
(Note: Ethanol is prone to absorbing moisture, which will reduce the octane rating. So it's suggested to replace E10 with fresh fuel at least every 2-3 weeks.)