The Core Chemical Advantages of Ethanol
Two primary chemical properties allow high-ethanol content fuel like E85 to produce more power in performance applications: its high octane rating and its high heat of vaporization.
High Octane Rating
Octane is a measure of a fuel's resistance to premature ignition, also known as engine 'knock' or detonation. The higher the octane number, the more compression and heat the fuel can withstand before spontaneously combusting. Standard pump gasoline typically has an octane rating of 87-93 (AKI), while E85 can rate around 100-105 AKI. This allows a tuner to increase an engine's compression ratio or boost pressure without risking damage from uncontrolled explosions in the cylinders. For high-performance vehicles, this increased resistance to knock is a primary reason for using E85.
Significant Cooling Effect
Ethanol has a much higher heat of vaporization than gasoline. This means that as it evaporates from a liquid into a gas, it absorbs a substantial amount of heat from its surroundings. When E85 is injected into the engine's intake manifold and cylinders, this evaporation process significantly cools the incoming air charge. Colder air is denser, allowing more oxygen molecules to be packed into each cylinder. The result is a denser air-fuel mixture, which produces a more powerful combustion event and increases overall horsepower. For a turbocharged or supercharged engine, this cooling effect is especially beneficial as it allows for higher boost pressures without the risk of detonation associated with high intake temperatures.
Performance Differences Between Naturally Aspirated and Forced Induction Engines
It is crucial to understand that the power benefits of ethanol are not universal across all engine types.
Forced Induction Engines
More Power For turbocharged and supercharged engines, the high octane and cooling effect of E85 are a game-changer. The higher octane allows for more aggressive timing and increased boost without causing knock. The cooling effect further enhances performance by creating a denser, more oxygen-rich intake charge. In a properly tuned forced induction vehicle, switching to E85 can unlock significant and dramatic power gains.
Naturally Aspirated (N/A) Engines
Less Power (Untuned) For a stock, naturally aspirated engine, simply running E85 will likely result in a power loss and reduced fuel economy. A stock engine's computer is calibrated for gasoline's stoichiometric air-fuel ratio (around 14.7:1). Because ethanol has a lower energy density and requires a richer air-fuel ratio (around 9.8:1 for E85), the engine will run very lean on E85, leading to reduced power and potential damage if not corrected with a proper tune. With significant modification and a dedicated tune, an N/A engine could see power benefits by running a higher compression ratio, but the gains are far less dramatic than in a boosted setup.
The Necessary Upgrades for Running E85
To safely and effectively use E85 for power gains, particularly in performance applications, specific engine modifications are required.
Fuel System Upgrades
Due to ethanol's lower energy density, an engine requires a significantly higher volume of E85 compared to gasoline to produce the same amount of power. This necessitates upgrades to handle the increased fuel flow.
- Larger Fuel Injectors: Stock injectors often cannot flow enough fuel to meet the demands of E85, especially under high load.
- High-Capacity Fuel Pump: The factory fuel pump is typically not designed to deliver the volume of fuel required for E85, especially in high-performance engines.
- Ethanol-Compatible Components: Ethanol is corrosive and can degrade older rubber and plastic fuel lines, seals, and o-rings. A proper E85 conversion requires fuel system components made from compatible materials.
Engine Calibration and Tuning
An engine's computer must be reprogrammed to take advantage of E85's properties. This involves adjusting the fuel maps to deliver the correct richer mixture and advancing ignition timing to exploit the higher octane rating. A flex-fuel conversion kit can be used to automatically adjust the tune based on the fuel's ethanol content.
E85 vs. Gasoline: Key Differences for Performance
| Feature | E85 (85% Ethanol) | Gasoline (E10) |
|---|---|---|
| Energy Content | Lower (approx. 27% less per gallon) | Higher |
| Fuel Economy | Lower (requires more fuel volume) | Higher |
| Octane Rating | Higher (typically 100-105 AKI) | Lower (typically 87-93 AKI) |
| Detonation Resistance | High (allows for more boost/timing) | Lower (more susceptible to knock) |
| Cooling Effect | Higher (reduces intake air temps) | Lower |
| Performance Potential | High (especially in forced induction) | Limited for performance modifications |
| Engine Compatibility | Requires flex-fuel compatible components and tune | Standard for most modern vehicles |
| Moisture Absorption | Hygroscopic (absorbs water, can lead to corrosion) | Non-hygroscopic |
Conclusion: More Power with a Catch
To definitively answer the question, "Does ethanol give you more power?", the answer is yes, but only under specific circumstances. For a stock, non-flex-fuel vehicle, running E85 is not recommended and will likely result in a decrease in power and fuel efficiency. However, in a performance-oriented engine, particularly one with forced induction, ethanol's high octane and significant cooling effect can be leveraged through proper tuning and fuel system upgrades to achieve substantial horsepower and torque gains. The key is understanding that ethanol is not a simple 'drop-in' power adder but rather a high-performance fuel that requires an engine and fuel system specifically configured to take full advantage of its unique properties. For the average driver, the trade-off of reduced fuel economy and potential long-term component issues means sticking with standard gasoline is the practical choice. For the enthusiast seeking maximum performance, however, ethanol can be a rewarding path to unlocking an engine's true potential. To learn more about how flex-fuel systems work, refer to the eFlexFuel blog.
