E86 gas is a high-ethanol fuel blend containing approximately 86% ethanol and 14% gasoline. It falls within the broader family of flex fuels commonly sold as “E85,” which despite the name can range from 51% to 83% ethanol depending on the season and region. An E86 blend sits at the higher end of ethanol content, sometimes slightly above the official spec range, and is most often encountered in racing and performance applications where maximum octane and cooling benefits matter.
How E86 Relates to E85
The label “E85” is somewhat misleading. The ASTM D5798 standard, which governs ethanol flex fuels in the United States, allows blends ranging from 51% to 83% ethanol by volume. Gas stations selling E85 may pump anything within that window. In winter months, the ethanol percentage often drops closer to 51% to help with cold starting, while summer blends trend higher.
E86 sits just above that official ceiling. You’ll typically see it sold by specialty fuel suppliers or blended by enthusiasts targeting a specific ethanol percentage for engine tuning. In practice, the difference between E83 and E86 is small, but tuners care about precision because even a few percentage points of ethanol change the fuel’s octane rating, energy content, and the air-fuel ratio an engine needs to run correctly.
Octane Rating and Knock Resistance
The main reason people seek out high-ethanol blends like E86 is octane. Pure ethanol has a research octane number (RON) well above 100, and blends in the E85 range typically deliver a pump octane (the number posted at the gas station) of around 100 to 105. The higher the ethanol percentage, the higher the octane. An E86 blend lands near the top of that range.
High octane means the fuel resists knocking, which is premature detonation that can damage engines. This makes E86 attractive for turbocharged and supercharged setups, as well as engines with high compression ratios. Drivers running forced induction can push more boost pressure without the engine knocking, which translates directly to more horsepower. Compared to premium pump gasoline at 91 or 93 octane, E86 provides a substantial margin of safety against detonation.
One nuance worth knowing: ethanol’s motor octane number (MON), which measures knock resistance under more extreme conditions, is relatively low compared to dedicated racing gasolines with similar pump octane ratings. This means E86 performs best in applications tuned specifically for it rather than as a drop-in replacement for race gas.
The Cooling Effect
Beyond octane, E86 offers a significant thermal advantage. Ethanol has a much higher latent heat of vaporization than gasoline, meaning it absorbs more heat as it evaporates inside the engine. When E86 enters the combustion chamber and vaporizes, it pulls heat out of the incoming air charge, cooling it substantially. Research on pure ethanol shows cylinder charge temperatures roughly 60°C (108°F) lower than with gasoline at the end of compression.
Cooler intake temperatures do two things. First, cooler air is denser, so the engine packs more oxygen into each cylinder, improving volumetric efficiency and power output. Second, lower temperatures further reduce the risk of knock, compounding the benefit of the high octane rating. For turbocharged engines, which generate significant heat by compressing intake air, this cooling effect is one of the biggest practical advantages of running E86 over gasoline.
Energy Content and Fuel Economy
The tradeoff with high-ethanol fuels is energy density. Standard gasoline (E10) contains roughly 112,000 to 116,000 BTU per gallon. Ethanol contains about 76,000 BTU per gallon. An E86 blend falls much closer to ethanol’s lower figure, meaning you need to burn more fuel to produce the same energy as gasoline.
In real-world terms, expect to use 25% to 30% more fuel volume on E86 compared to regular gasoline for the same driving distance. Your fuel economy, measured in miles per gallon, will drop noticeably. For daily drivers, this is a meaningful cost consideration. For performance and racing applications, the power gains and knock resistance usually outweigh the higher fuel consumption.
Tuning Requirements
You cannot simply pour E86 into a vehicle tuned for gasoline and expect it to run well. The stoichiometric air-fuel ratio for E85-range fuels is about 9.7:1, compared to 14.7:1 for gasoline. That means the engine needs roughly 30% to 40% more fuel injected per combustion cycle to maintain the correct mixture. Without a tune that accounts for this, the engine will run dangerously lean.
Flex-fuel vehicles (FFVs) handle this automatically. They have sensors that detect the ethanol percentage in the fuel and adjust injection and timing on the fly. Non-flex-fuel vehicles need either a standalone ethanol content sensor paired with a compatible engine management system, or a custom tune built specifically for E86. Many aftermarket tuning platforms support ethanol blends, and the conversion is common in the performance community. Fuel system upgrades, including larger injectors and a higher-capacity fuel pump, are often necessary to deliver the increased volume of fuel the engine demands.
Storage and Shelf Life
E86 is hygroscopic, meaning the ethanol absorbs moisture from the surrounding air. Over time, this water absorption degrades the fuel. While gasoline can sit for months or even a year with a stabilizer, high-ethanol blends are less forgiving. Depending on storage conditions, E86 can go bad in as little as three months, though well-sealed fuel in a cool, dry environment may last considerably longer.
If you store E86 outside the vehicle for more than about six weeks, use a sealed metal container. Ethanol degrades many plastics over time, so standard plastic gas cans are not suitable for long-term storage. Inside the vehicle, ethanol can also cause corrosion in fuel systems not designed for it. Rubber seals, certain fuel line materials, and older fuel tank coatings may deteriorate with prolonged ethanol exposure, which is another reason factory flex-fuel vehicles use ethanol-compatible materials throughout the fuel system.
Who Uses E86
E86 is most popular in drag racing, time attack, and street performance builds where the combination of high octane, intake cooling, and relatively low cost (compared to race gasoline) makes it an ideal fuel. A gallon of E85-range fuel at the pump typically costs less than premium gasoline, though the higher consumption partially offsets that savings. For dedicated race vehicles that only care about power, the economics are straightforward: E86 delivers performance closer to expensive race fuels at a fraction of the price.
Some daily drivers with flex-fuel vehicles also run high-ethanol blends year-round, especially in areas where E85 is widely available. The lower cost per gallon, combined with the satisfaction of running a renewable fuel (ethanol is typically produced from corn or sugarcane), appeals to a subset of drivers willing to accept the fuel economy penalty. For everyone else, E86 remains a niche fuel, valued primarily for its ability to safely extract more power from high-performance engines.