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Fuel octane rating for petrol (or gasoline) engines is a crucial factor in maximising engine performance and efficiency. This seemingly simple number on the fuel pump is a key indicator of a fuel’s ability to resist knocking or pre-detonation during combustion, which is vital for maintaining engine health and achieving peak performance.

Understanding the octane rating is essential when tuning an engine, as it directly affects how the engine can be calibrated and how it will perform under various conditions.

Now, I’m going to guide you through the basics and the no-so basics of fuel octane ratings, exploring its chemistry, its impact on engine performance, and its critical role in engine tuning.

sweetcorn corn crop E85 Fuel
© Michael Fischer

How is E85 made?

In simple terms, E85 fuel is produced through a meticulous process that begins with selecting high-sugar or starch-rich crops like corn and sugarcane. These plants are harvested and ground to release their fermentable sugars. The ground material then undergoes fermentation, where yeast converts the sugars into ethanol and carbon dioxide. Following fermentation, the mixture is distilled to purify the ethanol, and further dehydrated to achieve the necessary concentration. The final step involves blending this pure ethanol with petrol to create E85, a fuel composed of 15% petrol and 85% ethanol.

Pump E85 vs Race Fuel E85

Not all fuels are created equal. There are notable differences between E85 from the pump at petrol stations and E85 sourced from race fuel manufacturers like Renegade and VP Fuels. Knowing these differences will help you spend your hard-earned cash in the right place.

Pump E85

The E85 available at petrol stations is ideal for all vehicles with the capability to use E85. It will still offer the same higher octane rating and performance benefits mentioned, but its composition can vary. Pump E85 typically contains a blend of 51% to 83% ethanol, depending on the region and season. To mitigate the issue of an inconsistent fuel blend, consider integrating "inferred flex fuel" capabilities, or a fuel composition sensor (commonly known as a “flex-fuel” sensor) to monitor ethanol content.

Did you notice that I said the maximum ethanol content is 83%, not 85% for pump E85?

This is because the "85%" refers to denatured ethanol. This denatured ethanol already includes about 2% hydrocarbons making it unsuitable for beverage consumption, avoiding the imposition of beverage alcohol tax. These regulatory measures ensure E85 remains classified as fuel rather than consumable alcohol.

Race Fuel E85

On the other hand, E85 from race fuel manufacturers like Renegade and VP Fuels is formulated specifically for high-performance applications. Race E85 usually has a more consistent ethanol content, often closer to the 85% mark, ensuring more reliable performance. These fuels are meticulously refined to remove impurities and reduce water content, providing a purer product. The result is a more stable and predictable fuel that can maximise the power and efficiency of high-performance engines. Race E85 also often includes additional additives to enhance combustion and protect engine components under extreme conditions.

For daily driving and general use, pump E85 is typically sufficient and more convenient. But for those of you seeking peak performance, race fuel E85 from reputable manufacturers such as Renegade or VP Fuels would be the best choice. It offers the consistency and highest ethanol content available for E85 fuels.

drift, drifting, car, nissan, 370z
© Leif Bergerson

What are the benefits of E85 fuel?

The high ethanol content of E85 gives it a higher octane rating (knock resistance) compared to regular petrol, usually between 100 and 105. The higher knock resistance properties allow engines with higher compression ratios to operate without knocking in conditions that regular petrol from the pump would. With some ECU tuning, this can result in increased horsepower and torque.

A benefit that is often missed when it comes to E85, is its ability to raise the dynamic compression of an engine. Due to the increased volume of fuel required in the combustion chamber, E85 naturally boosts the engine’s compression ratio. Higher compression ratios translate to more power, as they allow the engine to extract more energy from each combustion cycle. Additionally, E85’s high resistance to knocking, thanks to its higher octane rating, enables engines to safely operate at these elevated compression levels.

One of the standout benefits of using E85 is its ability to achieve Maximum Brake Torque (MBT) more effectively compared to regular gasoline. MBT represents the optimal ignition timing for peak engine torque. Due to E85’s higher octane rating and cooler combustion properties, engines can run with more advanced ignition timing without the risk of knocking.

Speaking of the cooling effects, ethanol has a cooling effect in an engine due to its high latent heat of vaporisation. This means that ethanol absorbs more heat from its surroundings when it changes from a liquid to a gas compared to petrol. When E85 fuel is injected into the combustion chamber, the ethanol absorbs a significant amount of heat as it vaporises, effectively lowering the intake air temperature.

Performance benefits aside, E85 is also valued for its environmental benefits. Ethanol burns cleaner than petrol, producing fewer greenhouse gases and reducing the carbon footprint of your vehicle.

E85’s ability to burn cleaner also means that engines can maintain optimal performance over longer periods, with less carbon buildup. Keeping your engine carbon-free will mean it can run smoother and healthier for longer and also reduces the frequency of your walnut blasting maintenance for those of you who have engines with direct injection.
Oh, and one more great addition to the list of benefits; ethanol’s biodegradable nature means that spills and leaks have a less detrimental impact on the environment.

Who would have thought that a change of fuel could be beneficial to petrolheads and the earth? I’ll dub this eco-friendly engine tuning.

Can I use E85 fuel in my car?

Before making the switch to E85, it’s crucial to determine if your car is compatible with this type of fuel. Flex-fuel vehicles are designed to run on E85, petrol, or any blend of the two. These vehicles come equipped from the factory with the necessary components to handle the corrosive nature of ethanol and the different fuel ratios.

For older vehicles not originally designed for E85, compatibility can be more challenging. You’ll need to check if your car’s materials, especially in the fuel system, can handle ethanol. Rubber and certain types of plastic components may degrade faster when exposed to high ethanol concentrations, necessitating upgrades.

Steps to prepare your car for E85 fuel

Fuel system upgrades

Switching to E85 requires specific fuel system modifications:

  • Upgrading Fuel Injectors: E85 has a lower energy content than petrol, so your engine will need more fuel to maintain the same power output. Larger fuel injectors will help deliver the increased fuel volume required. The air-to-fuel ratio for E85 is approximately 9.8:1 compared to petrol’s 14.7:1.
  • Replacing the Fuel Pump and Fuel Lines: Ensure your fuel pump can handle ethanol. Consider replacing rubber fuel lines with ethanol-compatible materials such as PTFE (Teflon) to prevent degradation.

ECU alterations

Proper engine tuning is vital for running E85:

  • Engine tuning: The ECU needs to be recalibrated to adjust the air/fuel mixture, ignition timing, and other parameters for optimal E85 performance.
  • Fit a Flex Fuel Sensor: If your ECU has the capability, add a flex fuel sensor, which can help determine the ethanol content in your fuel to adjust the tune if you want to be able to alternate between petrol and E85. If your ECU is unable to support the integration of a flex fuel sensor, some ECUs may support “Inferred Flex Fuel” which uses the oxygen sensors in the exhaust to estimate ethanol content based on the air/fuel mixture. The ECU interprets these readings to determine the fuel type and adjusts accordingly.

A flex-fuel sensor isn’t mandatory, but it is strongly recommended. If you are willing to use E85 only, and only E85, you could tune your ECU to suit that particular fuel. Just don’t get caught short and fill up on regular gasoline. Your car engine will not like it at all and risk fatal damage.

If you have the ability to load different engine tunes, you could drain your tank when you change fuels and switch the map to match the fuel. I created an Ethanol Fuel Calculator so you can determine how much fuel to add to reach the desired ethanol content without draining your full tank.

Checking and Replacing Components

Check the condition of your gaskets and seals.

  • Inspecting and Replacing Gaskets and Seals: Ethanol can degrade gaskets made from nitrile rubber or natural rubber. Replace these with ethanol-resistant alternatives like Viton (fluoroelastomer), PTFE (Teflon), or silicone to ensure durability and prevent leaks.
  • Upgrading Spark Plugs and Ignition Components: E85’s higher octane rating allows for advanced ignition timing and higher combustion pressures. Upgrading to colder spark plugs helps manage the increased heat, but avoid going too cold to prevent fouling during cruising. High-performance ignition components ensure a strong, consistent spark, and adjusting the spark plug gap can improve reliability with E85.
Nissan, r35, GTR, fuel, fuelling
© Erik Mclean

Cost Considerations

Converting your car to run on E85 involves upfront costs, including new parts and a session with your tuner. However, in some areas of the world, if you’re lucky enough to get E85 at the pump, these costs can be offset by the lower price of E85 compared to premium petrol. But as I mentioned previously, due to the lower energy content of E85, you use more fuel to maintain the same power output, so it’s hard to say how much more (or less) fuel you would use. If you have to buy E85 by the can, the performance gains and environmental benefits can make the extra spend worthwhile if that’s your jam.

If you own a new car, it’s likely that you won’t have to do as much (if anything at all) to your car to run E85. If your car does require modifications, it’s worth checking how the modifications might affect your vehicle warranty, as some manufacturers may void the warranty if aftermarket parts are used or if non-approved modifications are made.

Real-World Experiences and Tips

E85 has a different chemical structure from petrol, so it’s worth mentioning some usage and safety advice that I picked up while handling Renegade race fuel at JBM Performance.

E85 fuel has a shorter shelf life compared to regular petrol due to its high ethanol content. Generally, E85 can be safely stored in a vehicle’s fuel tank for about 3 months under normal conditions. Ethanol is hygroscopic, meaning it absorbs moisture from the air, which can lead to phase separation and reduced fuel quality over time. It’s best to use E85 within 1-2 months of purchase. To extend its lifespan, keep the fuel tank sealed and store the vehicle in a cool, dry environment to minimise moisture absorption.

It’s not only the fuel in the tank you need to think about, Injector Dynamics stated the following:

“in hot, humid weather, the ethanol can absorb enough moisture to cause rust in the fuel injectors in less than a week.”

If you aren’t going to use your car for a while, empty the fuel tank of E85 (or whatever high-alcohol content fuel you have), replace it with petrol and run it for a few minutes to get it through the entire fuel system.

The moisture-related issues don’t end there. You’ll want to be changing your oil more frequently. E85 can lead to increased blow-by, where fuel passes the piston rings and mixes with the oil, diluting it and reducing its lubricating properties. This can result in increased engine wear and corrosion over time.

I’m sure you’re aware by now reading this far that E85 primarily consists of ethanol, and for the chemists reading this, you may know that ethanol has a limited isomerism. Whereas petrol is a complex mixture of many hydrocarbons, each with multiple isomers. This results in petrol having a richer variety of chemical properties compared to the simpler composition of E85.

Therefore, due to the differences, E85 requires careful handling due to its specific properties. E85 and petrol both have significant flammability risks. However, the higher ethanol content makes E85 more volatile and allows it to evaporate faster than petrol. This can increase the risk of vapour buildup, especially in confined spaces, making it crucial to handle E85 in well-ventilated areas. While the flash point of ethanol is lower than that of petrol, (meaning it can ignite at lower temperatures), it is also more conductive than petrol, which can pose a risk of static electricity build-up during fueling operations.

To ensure safety, handle E85 away from open flames, sparks, or sources of ignition. In case of spills, clean them up immediately using absorbent materials and dispose of them according to local regulations. If you are storing cans or containers of fuel, store them in a cool, dry place away from direct sunlight and extreme temperatures, ensuring the area is well-ventilated to prevent vapour buildup. Always have a fire extinguisher rated for flammable liquids nearby.

Prolonged exposure to E85 vapours or direct skin contact can be harmful, so wearing protective gloves and safety goggles is highly recommended.

To Corn-clude - Is E85 worth it?

Switching to E85 offers a multitude of benefits that everyone with a petrol-powered engine can benefit from; its higher-octane rating, ability to raise dynamic compression, and cooling effects can significantly increase engine performance, while its cleaner burning properties help reduce greenhouse gas emissions and engine wear. However, making the transition requires careful consideration of your vehicle’s compatibility and potential modifications to the fuel system, the engine’s tune and ECU-related components.

While most of you on here are likely looking to extract more power from your engine using E85, it’s worth remembering that E85 presents a viable, eco-friendly alternative to traditional petrol. Something that the government don’t seem to be paying attention to because they’re spending so much time on the decreasing demand for electric vehicles.

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