E85 is one of the best-kept value secrets in the Mustang world. It is the cheapest path to real, meaningful power on a Coyote, which is why the go-fast crowd loves it. But it is not just fuel you pour in and forget. Here is what you actually need to know before you run E85 in your Mustang.
Quick answer: E85 is a high-octane, ethanol-heavy fuel that lets a properly tuned Coyote make noticeably more power for very little cost. But it requires a supporting tune, and often supporting fuel system parts, to run safely. Do not just dump it in a stock tune. Tune for it, and it is one of the best bang-for-buck upgrades you can make.
Why E85 makes more power
E85 has a much higher effective octane than pump gas, which means it resists knock and lets a tune run more aggressive timing and boost. It also cools the intake charge. On a Coyote, a tune written for E85 can make meaningfully more power than the same car on 93 octane, and the fuel itself is often cheaper per gallon. That combination, more power for less money, is why it is so popular. Our tuning basics guide explains why the tune is doing the heavy lifting.
What you need to run it
A proper tune
This is non-negotiable. E85 changes how much fuel the engine needs, so you need a tune built for it. Running E85 on a gas tune is how people get into trouble. A dedicated E85 tune or a flex-fuel setup is the safe path. Browse custom tunes and tuners.
Fuel system support
E85 requires more fuel volume than gasoline to make the same power, so as you push harder you often need supporting fuel system parts, higher-flow injectors and a pump, to keep the engine fed. Under-fueling is dangerous. Browse fuel system parts.
Flex-fuel flexibility
A flex-fuel setup lets the car adjust to whatever blend is in the tank, so you can mix pump gas and E85 without swapping tunes. It is the convenient way to run corn when you want it and pump gas when you do not.
The tradeoffs, honestly
- Fuel economy drops: ethanol has less energy per gallon, so expect worse mileage. You make up some of it on cost per gallon, but range shrinks.
- Availability varies: E85 is not on every corner. Know where your stations are.
- Blend inconsistency: pump E85 can vary in ethanol content, which is why flex-fuel or careful tuning matters.
- Cold starts and storage: ethanol behaves differently in cold weather and if the car sits, so factor that in.
Emissions and legality
Fuel and tuning choices touch emissions equipment and rules that vary by state. Keep your setup street-legal for where you drive, avoid emissions deletes on a street car, and check your local and state laws before making changes. Browse tuning options responsibly.
Frequently asked questions
Can I just put E85 in my stock Mustang?
No. A stock gas tune is not set up for E85. You need a tune built for E85 or a flex-fuel setup to run it safely. Dumping it in without tuning is risky.
How much more power does E85 make on a Coyote?
A properly tuned Coyote makes meaningfully more on E85 than on 93 octane, thanks to the higher octane and cooling effect. The exact gain depends on your mods and tune.
Do I need bigger injectors for E85?
E85 needs more fuel volume than gas, so as power climbs you often need supporting fuel system parts. Mild setups may get by, but plan for fueling as you push harder.
Does E85 hurt fuel economy?
Yes, ethanol has less energy per gallon, so mileage drops. The lower cost per gallon offsets some of it, but your range decreases.
Is E85 bad for the engine?
Run correctly with a proper tune and fueling, E85 is a proven, safe way to make power. Problems come from running it on the wrong tune or under-fueling.
Build your E85 setup
Everything filters to your exact car. Browse custom tunes, tuners, and fuel system parts. For where power fits in the build, see our complete S550 GT mod guide, and follow your local emissions laws.
