Using E85 Ethanol Blends in BMW’s: Should You Do It?
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/
Well what are the proper specifications to run e85??
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.
Regards,
BMW Tuning