E85 is a high-ethanol fuel blend for spark-ignition engines, sold at around 4,900 public stations across the United States. Despite the name it contains between 51% and 83% ethanol by volume, with the balance made up of gasoline. Why it is not 85% →
Who can run it
Flex-fuel vehicles are designed for it. They carry fuel-system components rated for ethanol and either a content sensor or an adaptive strategy that lets the ECU adjust fuelling to whatever is in the tank. If your vehicle is flex-fuel, E85 needs no modification.
A non-flex-fuel vehicle needs both a calibration and, usually, fuel-system hardware. This is not optional. Ethanol requires roughly 30% more fuel volume than gasoline for the same air mass, and running it on a gasoline calibration produces a lean condition that damages engines.
Why performance engines like it
Two properties, mostly. Ethanol has a high heat of vaporisation, so it cools the intake charge substantially as it evaporates — denser charge, lower combustion temperatures. And it is highly knock resistant, which lets a calibration run more timing or more boost before detonation becomes the limit. On a boosted engine the combination is worth real power.
The trade-offs
- Lower energy density. Expect meaningfully worse fuel economy, and a fuel system that has to flow more.
- Availability. Roughly 4,900 public stations nationwide, unevenly distributed.
- Variable content. The reason this site exists.
- Material compatibility. Older fuel-system components may not be rated for high ethanol concentrations.
Blends between
You are not limited to straight E85. Mixing it with pump gasoline gives you any blend in between — E30, E50, E60 — which is how most tuned street cars actually run: enough ethanol to be worth having, within what the fuel system can deliver. That is what the calculator is for.
Written by the Palm Beach Dyno team — a Ford performance shop running dyno and remote calibration on gasoline, ethanol blends and E85. Last reviewed 4 August 2026.