Josha37

Ethanol has a higher octane rating but a lower amount of power potential. also takes more of it to have the right mixture. if you switch from gasoline to e85 you need 20% more fuel and will still make 10% or so less power if the engine is made for gas. if you run crazy race gas compressions e85 is street legal cheap race gas, in a stock engine it is a negative for performance. so as ethanol content goes up, power slowly creeps down.

the_duke

10% ethanol is going to make a marginal difference. Probably far less than what you gain by increasing the octane high enough to allow full spark advance. Of course full on E85 would require larger injectors and a different fuel map. And as you stated above no power gain on a naturally aspirated motor. Throw some boost into the mix and it's a different story. Probably why my turbo cars love the 93 octane with ethanol.

Josha37

I was just trying to answer your question. most 91 around here already has 10% ethanol in it. to mix enough in to correct octane I'd need to be around 30% ethanol which I have put in the audi before. (some stations have blue handles around here where you can get 30). and that is enough to take 2mpg off and make it start funny. it doesn't take much ethanol to change the way gasoline behaves.

Josha37

I'm a huge fan of e85, my last trans am I built a 12.2:1 383 lt1 to run e85 and throw 250 hp worth of nitrous at it on a regular basis. ethanol let me do some pretty crazy stuff to it. after 10-15% in stock-gasoline engineered engines it becomes a issue. my wife's 16 silverado with the new 5.3 makes a extra 40hp if you put e85 in it. but it has a ethanol content sensor, 2 different fuel/spark strategies, and enough compression to make use of it.