Why does an e85 tune offer more power?
 

If e85 has less energy density than e10 fuel (regular gas), then why do people get more power out if it?

I am moving to indiana, where e85 is cheap, so I was curious to know why this works. Most flex car owners day they get worse gas mileage due to less energy density so I would think worse performance too.

Also, is there anything I need to do differently in winter vs summer? I've heard that there are different blends.

Ethanol as a fuel is less prone to detonation than 93 octane fuel. You often see people quote ethanol's octane rating as 113, but this is misleading because they are not using the proper means of calculating octane to reach this figure. The actual octane rating is around 94-96. This resistance to detonation allows a tuner to run more aggressive timing while results in increased power.

While it is less prone to knock, it does have a lower energy content per volume of fuel compared to gasoline, which requires a tuner to provide more fuel to the engine to overcome this issue. This is why people see lower fuel economy while using E85. The lower price of E85 typically offsets this reduction in MPG.

There is a difference in formulation between winter and summer blends due to the fact that higher concentrations of ethanol have issues with cranking/running in lower temperatures, so a lower percentage is typically used in the winter months to combat this. This means that the percentage to ethanol from tank to tank can vary depending on the season and station you fill at. There are several methods to combat this irregularity, with a flex-fuel system being one way. A flex-fuel setup should automatically adjust the fueling to account for the variations in ethanol percentage with no action required by the end user.

I don't recall the exact percentage needed, but it's roughly 50% is all that is needed to get all the performance benefits of a ethanol based fuel while staying naturally aspirated, so there are tunes available that do not run a flex-fuel setup and they are typically just as safe to run as long as you only use E85 fuel. You will see a larger variation in fuel trims with this type of setup, but as long as the tuner has properly tuned the map, you should have issues as well. Depending on how cold it gets where you live, you may have issues cranking with this type of setup, but those issues typically only arise when you start getting into the low 30's and below. If you plan on swapping to 93 or 91 octane then you would have to reflash your ECU back to a normal gasoline map in those instances.

@Malt Great answer! Ive been doing research on E85 because I will be making the switch soon. Just to add a few things that I've seen or heard other users say. With the fuel economy, some have said they get 3-4 mpgs less per gallon while some have reported almost no change. In Cali, E85 is about a dollar cheaper per gallon, so even at 5mpgs less it would be worth the switch.

And for winter start ups, I've read that people will add a gallon or two of 93OCT to help the start ups.

If I where you, I would get that E85 option asap! Flex Fuel is an option as well. Ive been looking at the Open Flash Tablet because it will give me the ability to flash back and forth between the E85 tune and the 93OCT tune as there are only a few E85 pumps near me.

Timing, timing, and more timing.

e85 is WAY more knock resistant than 94 or 96 octane fuel.

Of course, but E85 also provides more of a cooling effect in the cylinder than gasoline does, which contributes to the knock resistance. I was merely pointing out that the claimed octane rating of E85 is typically grossly exaggerated. There is more to resistance of detonation than just octane. ;)

Ethanol specific energy at stoichiometric fuel air mixtures is actually higher than gasoline allowing a higher release of energy per lb of air burned than gasoline.

Typical gasoline Thermal energy 19,000 BTU/lb max power fuel air mixture 12.5:1
Typical E85 Thermal energy 13,475 BTU/lb max power fuel air mixture 6.975:1
Typical ethanol Thermal energy 12,500 BTU/lb 6.429:1

If you are consuming 100 lbs of air, lets see how much fuel energy you release for each of these fuels using gasoline as the base 100% reference.
100/12.5 = 8 lbs of gasoline @ 19,000 BTU/lb = 152,000 BTU = 100%
100/6.975 = 14.337 lbs of E85 @ 13,475 BTU/lb = 193,189.9 BTU = 127% more heat energy
100/6.429 = 15.555 lbs of Ethanol @ 12,500 BTU/lb = 194431.5 BTU = 128.9% more heat energy

Typical fuel energy contents:
gallon of gasoline = 125,000 Btu
1 gallon of ethanol = 84,400 Btu

So higher specific energy release of E85 at stoichiometric fuel air mixtures, Plus cooling effect, plus knock resitance is where you find all that power

Not disputing that at all! Just wanted to clarify that e85 will net way bigger gains than 94 octane gas, even if the effective octane is similar.

Keep in mind that even though you are going less miles on a full tank you are spending much less to fill up. For instance 93 is 4.15 a gal in louisville ky 4.15 x 11 gal 45.00 and you can get 330 miles to a tank. So that makes it cost you 13.6 cents a mile. E85 is 2.69 a gal x 11 gal 29.00 to fill up. You can get 250 miles to full tank of e85 so that puts you at 11.6 cents a mile. Just something to keep in mind, and the bump in power is nice.

Just don't trust the fuel computer for your consumption with E85 as they often read incorrectly. The way to accurately work out your consumption is set the trip gauge when you fill the tank, then when you re-fill it, divide the number of miles trraveled with the fuel it takes to fill the tank back to the top. In my experience I am using about 20-25% more E85 than regular pump gas. The fact that it is almost 25% cheaper for E85 down here means the cost is almost the same in real terms but I am getting more power, effectively free of charge :drool:

Not necessarily...

Say you have a vehicle with a well setup vehicle, such as JDL equal length headers, Airaid intake, full 2.5 inch exhaust system and custom tuned on 94 octane. I bet you would be hard pressed to make much more power on E85 because the ignition timing values will already be near the ideal maximum for the vehicle on this particular setup running 94 octane.

Now on a restrictive system, such as a completely stock vehicle then yes there is a lot of room for improvement because the timing values will need to be much lower in this configuration for 94 octane. This will allow the E85 to do its job and push the timing values to their ideal maximum for the engine and of course more power.

Cheers,
William Knose
Delicious Tuning

Little off topic but I don't want to make a thread.

Fuel injection cleaners:
Worth it?
Will I have any issues when mixing it with e85?

Thanks.

Unless people with well sorted 94 octane setups are hiding, the dyno plots don't seem to support that.

There's lots of people making well over 200whp on stock headers and intakes with e85, but I haven't seen anyone with 94 octane and full bolt ons matching the power.

Sure it isn't a 30whp+ gap, but it's still a gap.