​Ethanol (E85): Should You Use Ethanol Blends in Your BMW?

A quick Google search will reveal that there is no shortage of debates regarding the use of ethanol fuel. However, most articles focus on the sustainability and feasibility of ethanol fuels. Although sustainability is important to consider, the real question is whether or not higher ethanol mixtures increase engine longevity and performance in the long-term.

What is E85 Ethanol Fuel?

Before diving into the real question, I will start by giving some background on ethanol (e85) fuel. E85 refers to an 85% ethanol to 15% gasoline mix; most ethanol fuels are corn-based, and as such, E85 is considered to be a renewable fuel. As the impending consequences of global-warming loom around the corner, the United States government passed a mandate to require increasing amounts of ethanol in gasoline. Gas in the U.S. contains roughly 10% ethanol, and 90% gasoline; in other words, the gas that you fill up with at the pump is E10. Although ethanol is considered a renewable fuel the argument against e85 is the heavy demand it puts on water, soil, and food-supply.

E85 Ethanol Effects on Fuel Economy

BMW is one of the most sustainable and environmentally friendly automotive manufacturers in the world. However, for the true car enthusiast, this is only an additional benefit as most enthusiasts buy a BMW for one reason, to own the “Ultimate Driving Machine”. At first glance, it would appear as if ethanol would decrease power output because the British Thermal Units (BTU) rating is less than that of gasoline. A higher BTU rating indicates that gasoline creates more energy per molecule as compared to ethanol. However, e85 requires a higher amount of fuel (more molecules) to reach stoichiometric combustion, which means the overall BTU rating for each burn cycle is higher than that of gasoline. To put this simply, e85 has a higher octane rating than gasoline. On the downside, more fuel is required for each burn cycle, so e85 will actually lower your fuel economy.

E85 Ethanol Effects on Horsepower and Engine Longevity

Enough with the technical gibberish; what does this mean in terms of engine performance and longevity? E85 requires about 30% more fuel for combustion, which means internal cylinder temperatures will be reduced. Because air is denser at cooler temperatures e85 will allow for more air molecules in each cylinder, leading to an increase in horsepower. However, this is only one benefit of cooler cylinder burning temperatures. Heat is what puts stress on engine internals, so less heat will reduce the stress inside the cylinder. In addition, since e85 is harder to burn it will actually reduce the likelihood of engine knocks, pings, and misfires. This allows you to target more aggressive cylinder timing, which will also increase engine performance.

What You Need to Know Before Running E85 on Your BMW

Before running e85 mixtures here are a few things to consider:

-Does your BMW have direct injection? Since e85 requires 30% more fuel for each burn cycle, your fueling system must be capable of delivering enough fuel. Direct Injection is capable of supplying more fuel. The alternative option here is opting for a stage 2 or stage 3 LPFP. On your stock N54 LPFP, you can handle up to about 40% E85 blended with 60% of 93 octane pump gas. With a stage 2 or 3 LPFP, you can run 100% E85 which creates even more power and is actually cheaper!

-Does your BMW have stainless steel fuel lines? There are also debates on whether or not e85 will degrade fuel lines, seals, etc. To be on the safe side, I would recommend having stainless steel lines and injectors. Most newer, turbocharged, direct-injected BMW engines feature stainless steel lines and injectors that will not be affected by ethanol.

-Do you have aftermarket software? Your ECU/DME will also need to be able to flow more fuel. A stock BMW DME will be able to run mixtures around E20 without any issues. Aftermarket software and tuning will allow most direct injected BMW’s to run around E40 fuel before the low-pressure fuel pump cannot flow any more fuel.

As a fair warning, once you start running e85 there is almost no going back! Within months of using E85 I could tell my engine was running stronger, healthier, and cooler. Although E85 has great performance benefits, there is much more to it than simply putting E85 in the tank and expecting your car to perform better. To anyone interested in running E85 I would suggest doing a lot more research and ensuring you have the proper fueling system, modifications, etc. before fueling up with e85.

Stage 2 and Stage 3 LPFP's

There is no doubt Fuel-It! is the best in the game. Take a look at their stage 2 and 3 N54 offerings:

Stage 2: https://www.fuel-it.com/bmw-e-series-walbro-stage-2-lpfp-upgrade/

Stage 3: https://www.fuel-it.com/bmw-e-series-dual-walbro-stage-3-lpfp-upgrade/


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21 thoughts shared

  1. I have a 08 bmw 335i with a stage 2 fuel pump. And im getting tuned in a couple of days I wanted to know if I can run full e85 without putting bigger injectors?

  2. Hi,
    I have a tuned (to 760 hp but no dyno) 2018 M5. Is there anything that needs to be done before I start testing E20 up to E30? You know, I don’t what to ruin my engine or cause any new problems.

  3. I have a e90 328xi with the n52 and a stock fuel system. Would it be capable of running e85 as long as I have it tuned for it?

  4. Hi there !

    I am in France, here , E85 Is 0,60 cents of euro / liter , whereas 98 gaz Is 1,20 euro ( 1,6 euros /liter not so long ago )

    Car Is 435 i N55 , Can I run full 100 % E85 with a map and walbro lpfp ?

    I don’t necessarly need power upgrade , but in France, due to the price , éven if 25 % more consumption, this Is a good deal

    Manu thanks for your time

  5. what fuel mixture should i be using when going to e85 with 93 octane can not figure out the amount of gallons to use … bmw 2012 335i e93 n55 upgrades chargepipe fmic downpipes intake mhd ..exhuast . stock turbos how much e85 should i be mixing with 93 ocatane to get e30 for mhd stage 2 plus

    thanks bob

    1. Hi Bob,

      E30 will be just over 25% E85 and just under 75% 93 octane. Most normal pump gas contains about E10 fuel. As such, the calculation is:
      (.25 x 85) + (.75 x 10) = E28.75

      If you’re filling your tank from empty it would be about 4 gallons of E85 and 12 gallons of 93 octane. The exact mix will never be perfect, but if you stick right around 25% E85 and 75% 93oct you’ll be good. Also, E85 isn’t always exactly E85. I believe the standards are around E51 to E83 when you fill up at an E85 pump in the US.

      You can buy a cheap E85 test kit to read the exact E85 amount at the specific pump. I’ve personally never bothered since I stick with conservative tuning. You should be fine as well especially if you’re on the stock N55 turbo.

      Best Regards,

  6. So, I have a fully upgraded N54, including a Stage 2 Walbro 450 LPFP. I also have a custom MHD tune on the car, but I don’t know the specifics of that tune. Does that mean I can run up to 40% E85 now???

    1. Hmm that’s a tough one if you’re not sure what the tune was set up for. I don’t know if MOTIV can help you out, but I would try to get to the bottom of what the tune was setup for.

      If the custom tune is dialed in for E50 fuel you probably don’t want to be running straight pump gas or E30 mixes, for example. In that case the timing may be too aggressive for what you’re running fuel wise. On the other hand, if the tune is dialed in for pump gas then ~E40 may be too much. At the least you’d be leaving power on the table.

  7. Hi,

    great write up! But you did not mention S65 engine.. What mixture is it capable running with e85? I am also contemplating some buying Perflex Commander stuff, but now little confused how that will work. They advertise that you can run pure e85 with 85 percent ethanol, but if fuelling system is not capable handling that, so how it works then..

  8. Hi,

    Do you have any idea about the capabilities of n53 engine running mixtures of e85? Have you come across any n53s using e85, is it possible with a tune or do you have to change the injectors and hpfp?

  9. Comment author image

    Jeffrey J Wisuri


    So i have a f30 2016 340ix with Dinan v2, mpe, xph stage 3 tranny flash, catted DP and resonator delete. What % e can i safely use to start?

  10. Hi,
    What do you think about running an m135i (N55) with 100% E85 ? I am looking for fuel price economies, not additional power, but I don’t want to have issues with the engine. Is reprogramming the ECU enough to handle 100% E85? Do you think there are risks of damaging the engine on the long run (valve seats /corrosion etc… ?)

    1. Hi Garry,

      E85 would not have much benefit if you’re not doing it for performance reasons. 100% E85 would result in roughly 25-33% fewer miles per gallon. If you average 20mpg in the city on 91/93 octane then expect about 14-15mpg on E85. That just about wipes out the difference in price between the fuels.

      The stock fueling will not be able to keep up with 100% E85. You would need fuel pump upgrades to handle that much E85. All in all, we wouldn’t recommend heavy E85 mixes unless it’s for performance benefits.

      BMW Tuning

    2. Hi,

      I also own a BMW M135I N55 and I am looking for feedback on the conversion to ethanol. Have you reprogrammed your vehicle? If so, what is your feedback?

      Thank you

      1. Hi Severin,

        When it comes to running higher ethanol mixes on the N55 you will need a tune. The stock DME tuning should make the necessary adjustments to fuel flow, but you won’t see any real performance or power benefits without a tune.

        PWG N55 engines can generally handle about E30 on the stock fueling system. The newer EWG N55 is generally limited around E20 to E25. Both may handle a bit more on healthy fueling systems. We have a guide for N55 fueling mods, so feel free to check it out for more info on E85 blends in the N55 engine. https://bmwtuning.co/bmw-n55-fueling-mods-guide/

        Best Regards,

    1. Hi Diaz2k,

      Proper specs to run E85 depend on each specific engine in question. Most modern turbo BMW engines are capable of running 30% E85 mixtures with a tune only. However, for example, fuel trims become an issue on the S63tu engine. I’m blanking on the exact part that is needed but I believe there is an additional sensor that can be run with the JB4 tune on the S63tu engine to assist in running up to 30% E85. The S55 powered M3 is capable of running well over 50% E85 on stock fueling with a tune.

      On the N54 you can dump in 30-40% E85 mixes with a JB4 tune only. No other mods required. In order to run over 40% you will need an upgraded LPFP. You might be able to run 100% E85 with a proper low pressure fuel pump. However, horsepower also comes into play. If you’re on upgraded turbos pushing 550+whp you will cap out the direct injection running full E85. As such, you will need port injection to support heavy E85 mixes.

      Unfortunately, the answer is not so straight forward. There are tons of factors. Ultimately, we recommend starting with a small mixture (say 20-25% E85) and running some data-logs. If fuel pressures and fuel trims check out then test 30% on the next fill up. You can keep going until you find the limit. We don’t advise just showing up and dumping 40% E85 in the tank if you have never experimented with E85 before.

      On our N54 335i, for example, we initially started running 20% E85. After a few tanks we bumped up to 30%, 35%, 40%, and eventually 45%. It became clear that our specific N54 was completely maxing out the LPFP on 45% E85. As such, ever since then for the last 3-4 years, we’ve opted to run ~35% E85. It’s plenty to reap the benefits of E85 while keeping the fueling system a decent bit under it’s maximum.

      BMW Tuning