Tuning for E85 Vs 91
 

Hey all,

Bear with me here, I'm VERY inexperienced in the car scene, everything I know thus far has been from forum perusing/limited hands on experience.

I was just curious about all of the tuning threads I've been perusing.

Basically, if you flash your ECU to a tune from a company such as ECUTEK, you can run E85 fuel from my understanding, correct?

So basically, run your tank dry, flash, and then you can run a completely different grade of fuel. E85 out here is about 3.50 a gallon I believe (unless I'm reading the wrong signs.)

This won't affect anything at all in your car from switching from 91 to E85? What's the difference between the two? What sort of gains would your vehicle expect to see from such a switch? MPG Gains? HP/TQ Gains? Is it worth the money in the long run? What about warranty voiding?

I'm really just looking for a straight up pros and cons selection from you guys. /Bash for my noobiness if you must, but I'm really interested in learning to see if this is something I should consider doing to my FR-S. I'm really getting into the aftermarket scene.

Take into consideration that I most likely will NOT be tracking this. My FR-S is a daily driver that's used about 70% city/30% highway. (I live in Las Vegas.) The only aftermarket performance mod I currently have installed is an Airaid Dry Filter CAI, and in a few days a HKS Spec L Cat back exhaust.

Thanks guys, I appreciate it.

-Ben

At 3.50 a gallon you're not going to save much money if any at all. Think of it as a cheap race fuel that you get power for free from.
The pro is if your car is tuned for it, you get some amount of power for free, no mods. The cons are you need to refuel more often and you'll probably spend a tiny bit more on fuel (hard to say how much).

Premium out here is over $4.00 at the moment. Do you lose MPG using E85 instead of 91?

"over 4.00" LOL man, I paid 4.59 a gallon for regular last week. Previous fill was 4.29. I saw premium going for over 5 dollars a gallon at a Chevron in the South Bay.

Yes you lose MPG, how much is hard to say. Figure 20% less mpg minimum, it's as bad as 29% in some cars but this motor is direct injected so it should fare a bit better. So it's almost certainly going to cost you more...just think of it as super cheap 100 octane race gas (except it's even better than 100 octane race gas) that's not much more expensive to run daily than premium. If E85 is 3.50 a gallon think of that as being equivalent to 4.70 a gallon normal gas. The rule for saving money on E85 usually is don't buy E85 unless the price is more than 30% cheaper.

I feel your pain with gas prices, I was simply making a comparison so I could see which would be economically feasible for everyday driving. So really, 91 is the best route to go unless I plan on tracking it very frequently, which I don't, correct?

Well the thing is, E85 gives a noticable power boost compared to normal gas, on the order of 5-10% (direct injection motor should see a bit more). So the car will be a little quicker if you use E85 all the time, you just pay a little more to have that fun.

Interesting. And that would be, let's say, a 5-10% gain on a purely STOCK car? What about a vehicle that's been aftermarket modded (Exhaust, intake, etc.) would you see bigger gains when using the E85? Thanks for your help man, it's appreciated. :respekt:

Yea, E85 will make 5-10% more power than gasoline all else equal, typically. For example, Formula SAE allows you to use either 100 octane gasoline with a 20mm restrictor or E85 with a 19mm restrictor, because E85 gives more power per unit air.

Interesting. Thank you for the insight bro! Much appreciated.

A short trip back to chemistry class will demystify the whole thing.

Gasoline is made up of 100% hydrocarbons. We'll ignore the impurities to keep it simple. These are long chains of hydrogen and carbon, and when you combine it with oxygen at high temperatures, it burns.

Ethanol is made of hydrogen, carbon, and oxygen (C2H6O). By weight, ethanol is almost 35% oxygen, leaving 65% for hydrogen and carbon, and all air/fuel mixtures are done by weight.

E85 is ~85% ethanol, and ~15% gasoline. (but it varies) 85% of 35% is close to 30%, so E85 is almost 30% oxygen. This leaves you with 70% of the hydrogen and carbon per unit you were injecting with pure gasoline.

What this means is, you have to inject more fuel (hydrogen and carbon) to get the same amount of power. The bonus is that you get more oxygen than air will provide on it's own, which means you can burn a bit more fuel, and make a bit more power.

Chemistry was never my strong point in high-school. Thank you for clarifying this though! I appreciate the insight. :respekt:

The downside is that there has been ZERO DURABILITY TESTING ON E85. NONE. A few people have been driving around for a couple months with it. I guess to most people on here, if it doesn't break immediately it must be fine. That being said, if you ran one or two tanks of E85 here and there I wouldn't be concerned, but sustained use is a big deal.

I know saying this ruffles feathers. I know vendors make money selling E85 tunes as having basically no downsides besides lower gas mileage. If you have a basic daily driver with a bolt on or two, do you really want to subject your high pressure fuel pump and direct injectors to a fuel it hasn't been designed for? Those are the two biggest failure points in a direct injection system. They cost a lot of money to fix.

Will it void your warranty? If they figure it out and the individual dealership cares enough, then hell yes it will.

If these cars were 6-7 years old, off warranty and with a lot of knowledge built up about them, I'd say it's not a big deal to go for it. It's just stupid for a daily driver to steadily use the stuff. A track toy is another situation.

The other side is, if no one is daring enough to try it, there will never be definitive long term testing.

Pay to play, as they say. If you have to know the answer before you start, then it's best to follow in the footsteps of braver and more curious souls. Just remember this when things do fail for those people, give them thanks for saving you rather than ridicule for failing. Failing is the fastest way to learn new things.

That's a good way to look at it. It's too bad that most people don't understand the risks, and vendors aren't helping. People think it's not a big deal because they read some guy on the internet doing it. You can't draw that conclusion when the vehicle has been in service for 6 months.