Mailbag: What Do I Need to Run E85 Fuel?

This E85-specific carburetor from Quick Fuel is one example of how chemical differences between gasoline and E85 fuel require certain parts upgrades in order for ethanol to perform at its best, and to prevent damage to parts designed for gas engines. (Image/Holley)

Q: I want to run E85 in my car. What should I know before changing fuels?

A: Many of us have seen the cars making huge power on E85 and naturally want to know more.

First, you can’t just switch fuels from gasoline to E85. Your performance will suffer, and you can damage parts by doing it.

Does E85 make more power than gasoline?

It can.

E85 contains less energy per gallon than gasoline.

But, an engine designed specifically for E85 can make more power. The trade-off is that it requires more fuel.

More fuel volume and the chemical makeup of E85 keep the air/fuel mix cooler. E85 also has a higher octane rating than gasoline, which increases:

  • Ignition timing advance
  • Compression
  • Boost

How can E85 damage parts?

E85 has a different chemical makeup than gasoline, and some of those differences can damage rubber parts.

Also, hot spots in the combustion chamber can cause pre-ignition.

The Basics of Switching to Ethanol​​​​​​​

The fuel system must be designed to deliver more fuel for E85 to be effective.

Every part of the system needs to be alcohol compatible. Parts to consider include:

E85-ready carburetors are available. Some are coated to prevent corrosion. They have updated floats and larger jets. The internal passages are also enlarged to handle more fuel. E85 conversion kits are available for some carbs.

E85-ready fuel injection kits are also available. The ECUs are programmed to work with E85. They have the right seals and O-rings. More good news—they also work with gasoline. If you upgrade to fuel injection and you might ever run E85, just buy a compatible kit from the start.


  • Some fuel injection kits can be ‘tricked’ into providing enough extra fuel to work with E85. This must be researched on a case-by-case basis.
  • Fuel injection kit max horsepower ratings are based on gasoline. The horsepower capacity of the kit will drop 30 percent when used with E85.

This is another in a series of weekly Q&A Mailbag sessions with Summit Racings tech department, in which there are hundreds more. Click here to see them all.

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  1. To make the question simpler, If I found myself in a ‘pinch’ needing gas in the middle of nowhere and E85 was the only thing available, would topping off my tank with E85 on a one-time basis get me back on the road? Would the car run OK?….Any short or long term damage? I have a bone stock 1994 5.0 Cobra Mustang with 75,000 t5ouble-free miles. Despite the Owner’s Manual recommendation, I’ve been running 87 octane regular for 20+ years.

    • This would depend upon how much E85 you are mixing with pump gas. For example, if you had a half-tank of fuel asn was “forced” to mix with E85, the mixture would be closer to E50, which you might get by with for a short-term solution. The engine will require richer air-fuel ratio but a good EFI system will be able to respond to that – there are many factors that ocmeinto play – too many to discuss here. One advantage to mixing is an incerase in octane rating. An E30 blend of ethanol and 91 octane gasoline will deliver an honest 93 fuel and it will cost less. In certain applications some new car testing has uncovered that tan E30 blend will improve mileage because the engine is no longer retarding timing from the detonation sensors. I would start by trying an E20 blend with a small amont of fuel like 4-5 gallons and see what happens. You may discover the engine positively responds to the higher octane – and you’ll find the price for that octane fuel is less than regular pump premium.

    • My question is also simple. If you were “in a pinch”, why would you be topping off? If you had that much gas in the tank, then you wouldnt be in a pinch. To interpret what you are saying, you would be putting the e85 in full mix to get to another place, then putting gas in after the fact. So the basis of your question becomes, not so simple

  2. Go on run E85 and you will never make 75,005 trouble free miles. You refuse to follow the manufactures recommendations on fuel for the vehicle so why ask the question here. You have already shown you believe you are smarter than Ford Motor Engineering, and if you don’t like the answer you get on here you will do what you want once more.

    A Retired FoMoCo Engineer

    • Daniel Wilson says:

      I have to fully agree with Sam’s comments about the’94 Mustang Cobra owners blatant disregard of Fords recommendation to use a higher octane fuel. Even if there’s not any obvious signs of engine damage from using the wrong fuel, there’s probably a substantial amount of power being left on the table because the EEC has altered the engines tune to compensate for the cheap fuel being used. There’s no point in owning any type of performance vehicle if everything to optimize the output isn’t being done.

      I have a 1987 Thunderbird Turbo Coupe that I’ve owned since it was new. It has a dash mounted switch that can be used to select between regular and premium fuel. I leave it set for premium because 93 octane is readily available in the Atlanta area. In the regular fuel mode, it drastically alters the EEC-4 tuning parameters by limiting the timing advance and maximum turbo boost level. The performance drops off noticeably and with only 140 cubic inches in a heavy car like the T-Bird, it needs all of the power it can spool up. The EEC-4 power train computer can compensate for several variables but I don’t know how it would handle higher levels of ethanol fuel. I’m sure E-85 would be a bad idea in stock trim.

  3. Ethanol does not damage parts. Ethanol is compatible with more types of rubbers, plastics, and metals than gasoline and aromatics.

    The energy content of ethanol vs. gasoline is irrelevant. Performance of a gasoline-optimized engine MAY suffer when using an ethanol-gasoline blend, but it’s because the engine is optimized to run on the burn/ignition characteristics of gasoline, not because of energy content. Some ethanol-gasoline blends can provide better performance than gasoline even in gasoline-optimized engines.

    Why Do Small Engines Suffer From Ethanol Problems?

    The Irrelevance Of BTU Rating – Big Oil’s Gimmick To Hoodwink The Public

    The Irrelevance Of BTU Rating – Revisited

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