The EPA just approved E15 (15% ethanol blends) for cars built in 2007 or later.

http://news.pickuptrucks.com/2010/10...-vehicles.html

Will this have any affect on the stock or custom tunes? (i.e. causing the overly rich stock tune to run slightly leaner)

or

Will it be just business as usual?

 

Slightly worse mileage, and a bit less knock

Ethanol actually raises the octane rating..kind of.

 

Well, ethanol raises the octane, but the blend of gas it will be mixed with will likely still be presented as 87, 89, 91, 92, or 93 ... it just won't be as refined before they add the ethanol.

Most of the ethanol mixing sites say that the best fuel economy actually occurs at around 30% e, 70% gas... however I don't necessarily see how that is possible without timing / mechanical changes since ethanol contains ~30% less energy per volume than gasoline.... however the slower and more consistent burn may actually work in favor of that. It depends on quite a few factors though.

 

Each 10% of ethanol in the fuel requires approximately 3.5% more fuel. So 15% would be around 5% more. This would be enough to theoretically warrant a scale down of the injectors. However the real problem is going to be that the fuel retailers don't actually tell you what you are buying. You have to figure it out yourself.

The pump placards will say "May contain up to xx% ethanol", but it could contain zero, or anything in between. This is what is most annoying to me about the whole ethanol in fuel thing.

The short answer is yes, maybe. It would depend on how much cushion your custom tune has on its fueling. If it has a 4% cushion (ie 11.1 afr) then it likely won't matter. If it has a zero percent cushion, then it could.

In the Houston area, I have found from data logging, that Shell is the most likely to have alchohol in its gasoline, (of the "Name brand" retailers), and Cheveron the least. (I never had a noticeable fuel trim change from one tank of Chevron to the next, ever). Exxon seems comparable to Chevron, but I don't fuel as much there, so I don't have very much data.

Please note that the Shell gasoline always gave me close to the same trim correction vs. Chevron, so I am going to assume that their fuel blend is consistent, wich is good. (I don't want people to think I knocking Shell, because I am not)

It might be useful for people to log fuel trims before and after fueling, and see if there is an significant change from one brand to the next by region, and perhaps keep track of it here somewhere. (assuming it hasn't been done already)