Upgrading Your Car to Run E85: The Basics

There is a lot of confusion about tuning around E85, and a lot of terminology is tossed around that adds to the confusion. Almost any car can run E85 with the proper tuning and fuel system, but there is a difference between tuning for E85 and an E85 tune. Let’s dive into this crazy, confusing mess.

First, whether you have a Honda Civic, a 5.7 Hemi RAM, or an Audi S6, you can upgrade your car to run E85. There are a few ways to get there, but the first question is always whether the car’s factory fuel system can handle the high fuel volume requirements of E85. Of course, if your vehicle has a flex fuel badge on it, then it is ready to go to the E85 pump from the factory, but if not, the factory fuel injectors and/or fuel pump may not have enough capacity to do the job. 

Performance Flex Fuel Systems: Understanding Capacity

When we make a performance flex fuel system at Advanced Fuel Dynamics, we always put the car on our lab quality dyno first, so we can test the factory fuel system for capacity. We only sell systems for vehicles that have enough fuel system, or we make sure customers know they need an upgrade. Your local dyno shop can do the same for you if your vehicle is not on our product list. Often, full builds will need bigger fuel delivery, and we can help you choose the right components to make your engine safe for E85.

Managing Fuel with E85: ProFlex Commander and FlexLink Sensor Kit

Once you’ve determined that the car can handle E85 from a fuel capacity standpoint, it’s time to choose how to manage the fuel. Essentially, E85 requires the engine management computer to command much more fuel per cycle of the injection system. 

The easiest way to manage flex fuel is to install a ProFlex Commander from Advanced Fuel Dynamics. This patented flex fuel management system is easy to install, does not require any tuning at all, and works in real time, so you can fill up with gas or E85 anytime and roll on the go pedal with no delays. If your car isn’t covered by our Commander line, then the next most popular way to run E85 is with our FlexLink sensor kit and a fixed map E85 tune. Unlike a flex fuel system, an E85 tune is for one fuel and one fuel only: 85% ethanol fuel. You won’t be able to run gas, but you will get good results from E85. 

Tuning for E85 vs. E85 Tune: What's the Difference?

But an E85 tune is not tuning for E85. That is a whole different ball of wax. Tuning for E85 entails putting your car on a dyno and fine-tuning the engine management computer to maximize results when running E85. It is a much more lengthy process and can be expensive.

If you have a fixed map E85 tune and will only run E85, tuning for E85 is not a bad thing. You can pick up a little horsepower and gain some fuel mileage from a well-oiled custom tune. But the story is much different if you have an adaptive flex fuel system from Advanced Fuel Dynamics or from the factory.

After logging thousands of hours on our dyno with every kind of car, and even some motorcycles, and playing with the tunes, we have surprisingly found that a pump gas tune is best for flex fuel-equipped rides. Here is why. Especially on naturally aspirated cars, the typical methods for tuning by advancing spark timing did not return much gain. E85 is very different from gas and makes additional power because of its unique burn properties, not because of advanced timing like high-octane gas. By running a stock or pump gas tune, you may leave 3–4 wheel horsepower on the table, but your car will still be "flexible,” meaning you can still run gas or E85 anytime without worrying about the tune.

Surprisingly, forced induction engines on our dyno have actually made more power on E85 by retarding spark a little bit, explained by the faster burn event of E85. Again, this is not the same as gas tuning at all.

The bottom line is that tuning for E85 can be mildly beneficial, and if you have a fixed map E85 tune, it might be worth a little horsepower, especially if you have a turbo or supercharger on board. But if you have a flex fuel system and natural aspiration, it is far better to save your time and money by running a stock tune or good 91/93 tune and keep your car fast, safe, and reliable with either fuel.