E85 is a fuel blend consisting of 85% ethanol and 15% gasoline, though the exact ethanol content can vary regionally and seasonally. This fuel has gained popularity among performance enthusiasts because it offers significant power-boosting potential, but only when paired with necessary engine modifications. The ability to increase horsepower comes from ethanol’s unique chemical properties, which permit an engine to operate under more aggressive conditions than traditional gasoline allows.
How E85 Boosts Performance
The performance advantage of E85 stems primarily from two distinct chemical characteristics that allow a tuner to safely increase the engine’s output. The most widely recognized property is its high octane rating, which typically falls between 100 and 105. This high rating indicates a strong resistance to pre-ignition, often called knock or detonation, which is the self-ignition of the fuel-air mixture before the spark plug fires.
This stability permits the engine control unit (ECU) to be calibrated with a much more aggressive ignition timing curve, advancing the spark to extract more energy from each combustion event. For engines utilizing forced induction, such as turbochargers or superchargers, the higher octane allows for a safe increase in boost pressure. This ability to run higher compression, more boost, and more advanced timing is the direct mechanism that translates to a measurable increase in horsepower and torque output.
The second performance-enhancing property is ethanol’s high latent heat of vaporization. This refers to the substantial amount of heat energy the fuel absorbs from its surroundings as it changes from a liquid to a vapor state. When E85 is injected into the intake manifold or directly into the cylinder, this process draws heat out of the incoming air charge.
Cooler air is denser, meaning a greater mass of oxygen can be packed into the cylinder for combustion. This cooling effect also lowers the combustion chamber temperature, further increasing the engine’s resistance to knock. This mechanism acts like a built-in cooling system, enabling the engine to safely handle the stress of higher power output.
Necessary Engine and Fuel System Upgrades
A standard gasoline engine cannot simply run E85 because the fuel has a lower energy density than gasoline, requiring a much greater volume for proper combustion. To maintain the correct air-fuel ratio, E85 requires an increase in fuel flow of approximately 30% to 40% compared to gasoline. This necessitates mandatory upgrades to the vehicle’s fuel delivery system.
The fuel injectors must be upsized, often by 30% to 50% larger than the factory units, to handle this increased flow. Simultaneously, the factory fuel pump must be replaced with a high-flow, E85-compatible unit designed to deliver the higher volume of fuel demanded by the engine. Since ethanol is corrosive, these components must feature materials like stainless steel internals to prevent degradation and failure over time.
Engine tuning is required, where the stock Engine Control Unit must be recalibrated. The tuner adjusts the fuel delivery tables to ensure the correct volume of E85 is injected and modifies the ignition timing map to exploit the fuel’s high-octane rating. Without this specialized calibration, the engine would run dangerously lean on E85, leading to poor performance or catastrophic engine failure.
Many performance enthusiasts install a flex-fuel sensor, which measures the ethanol content in the fuel line (ranging from E51 to E85). This sensor allows the ECU to automatically adjust the fuel and ignition maps in real-time based on the exact ethanol percentage. This is crucial due to the seasonal and regional variations in pump E85 blends.
Practical Considerations for E85 Use
While E85 offers performance gains, the fuel’s lower energy density means that a higher volume is consumed to travel the same distance, resulting in a reduction in fuel economy. Vehicles running E85 typically see a reduction in miles per gallon of around 20% to 30% compared to gasoline.
The availability of E85 fueling stations is significantly lower than that of gasoline, making long-distance travel difficult and requiring careful route planning. Furthermore, pump E85 has seasonal variations, as it is blended with more gasoline in winter months to aid in starting. This fluctuation means a fixed tune calibrated for E85 in the summer can be unsafe or suboptimal in the winter without a flex-fuel sensor.
Cold-weather starting presents another challenge due as ethanol does not vaporize as easily as gasoline in low temperatures. This leads to a poor air-fuel mixture that is difficult to ignite. This often results in extended cranking times or the engine failing to start below approximately 40°F, requiring the ECU tune to be calibrated with fuel enrichment during the cold-start sequence.