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E85

Car culture term

E85
Photo: Mariordo Mario Roberto Duran Ortiz / Wikimedia Commons · CC BY-SA 3.0

What is E85?

A fuel blend of 85% ethanol and 15% gasoline. Higher effective octane than gasoline. Common in performance tuning for additional power.

E85 is a fuel blend of 85 percent ethanol and 15 percent gasoline. The high ethanol content provides several performance advantages: higher effective octane (105-115 RON equivalent), greater cooling effect on the intake charge (ethanol has higher latent heat of vaporization), and lower combustion temperatures than gasoline. The result is significantly more power potential when the engine is properly tuned for E85.

The downsides of E85 include lower energy density (ethanol contains less energy per gallon than gasoline, so the engine consumes more fuel volume) and corrosion concerns with older fuel system components. Modern Flex-Fuel vehicles are designed to handle E85 directly. Other vehicles require fuel system modifications (E85-compatible injectors, fuel pump, fuel lines) before reliable E85 operation.

E85 availability varies by region. The Midwest (Iowa, Illinois, Minnesota) has the most extensive E85 station network due to ethanol production. Coastal regions have less availability. Some racing and performance tuners blend their own E85 from pure ethanol and gasoline at the pump for more consistent ethanol percentage (pump E85 can vary from 51 to 83 percent ethanol depending on season and station).

What octane is E85?

E85 has an effective octane rating of roughly 100 to 105, well above premium pump gas. The high ethanol content resists knock, which is why tuners use it to run more boost and timing for extra power.

How is E85 made?

The ethanol in E85 is produced by fermenting and distilling plant sugars, usually from corn in the United States. That ethanol is then blended with about 15 percent gasoline, which adds the volatility needed for cold starts.

Related terms

OctaneKnockECU tune

Frequently asked questions

How much more power does E85 add?
On a properly tuned car, typically 20-50 horsepower over the same car on premium gasoline (depending on the engine and tune). The benefit is largest in turbocharged engines where E85 cooling effect on the intake charge allows more boost. Naturally aspirated cars see smaller gains from E85.
What modifications are needed for E85?
For Flex-Fuel cars (badged with the Flex-Fuel emblem), no modifications. For non-Flex-Fuel cars, typical upgrades include larger fuel injectors (E85 requires 30-40% more fuel volume than gasoline), upgraded fuel pump capacity, E85-compatible fuel lines, and an ECU tune for E85 operation. Cost typically $1,000-$3,000 for the conversion.
Does E85 hurt fuel economy?
Yes. Ethanol has lower energy density (about 30% less than gasoline). A car running E85 consumes 30-35% more fuel by volume than the same car on gasoline. The cost per mile is similar to gasoline if E85 is priced 25-30% lower than gasoline; E85 typically retails 15-25% lower than premium gasoline.
Can I run E85 in cold weather?
Cold-weather E85 has special blends (sometimes called E70 in winter months) with reduced ethanol content for better starting. Pure E85 can have cold-start issues below freezing. Modern Flex-Fuel cars handle this transparently. Aftermarket E85 conversions may need cold-weather considerations or fuel additives.
Is E85 corrosive?
Ethanol is hygroscopic (attracts water) and can corrode some metals and rubber components. Modern fuel systems (post-2000) are typically E85-compatible. Older cars with rubber fuel lines, certain metal components, or original fuel pumps may experience corrosion or failure with E85 use. Conversion to E85 requires verification of component compatibility.

E85 on the blog

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