Tuning For E85 Fuel

Steps to properly convert a car to ethanol


Written by: enginebasics.com

For an owner or tuner that has never tuned an E85 vehicle it can be a frustrating experience. First, if you don't know much about the background of E85, what it is, how much ethanol a fuel contains or any other basic facts, be sure to check out this article. If you are already familiar with the fuel then tuning a vehicle will be a cake walk.

Background to know before tuning

First remember that ethanol, like other alcohol-based fuels, is a corrosive fuel when compared to gasoline. Knowing this we need to remember to use appropriate fuel lines, fuel filters, and fuel pumps. Also take note that these types of fuels can be corrosive to aluminum. Before you panic. Most users have found that cars made after the year 2000 don't require an upgrade in the fuel lines, and that while the fuel is corrosive to aluminum, it has no wear effects on the motor. Some automotive owners have complained of problems when using E85, and other alcohol based fuels in aluminum fuel cells, while others have noted that as long as the fuel is not stored in the tank, there is no problem. Personally I run an aluminum fuel cell and have had no problems, but I drain my fuel cell for 8 months out of the year.

Next thing to focus on will be the fuel supply. Most engine set-ups will need a complete overhaul in this area being that E85 requires 30% more fuel to reach the same stoic conditions as gasoline. Meaning the fuel lines will need to be bigger, the pump will need to be upgraded, and the fuel injectors will need to grow as well. Many OEM vehicles stock fuel lines will be able to flow enough for 500-600 whp, but over that, growing the lines will probably be in order.

Tuning the ECU for E85

Ignition Timing

One of the great things about E85 is not only its higher octane rating, but also its ability to suppress detonation. Because of this, the timing map can be made to be more aggressive than when tuning with gasoline. Since everyone always wants numbers, I have always been safe in advancing the map 2 degrees everywhere to start with. From there I have been able to go as much as 6-7 degrees at times, and at other times I haven't been able to increase it at all after the initial 2 degree increase. Really it just depends on the set-up. ALSO, if playing with the timing of the vehicle, it is strongly encouraged that this be done on a dyno. Relying on just a knock sensor and a pair of det cans at times is not enough. For forced induction motors, E85 gives you the ability to run more boost without running into cylinder pressures that would normally cause the engine to knock. E85 seems to mainly be used on boosted applications for this purpose, but I have tuned several cars that were N/A, but running E-85, because of their 14:1 static compression ratio. If the motor is forced induced, many tuners and owners spend much of there time tuning the area of the map under boosted load. Remember though, tuning in the area outside of boost is just as important, and not for just drivability either. Many gains can be found in this area for performance since a proper timing curve will aid in turbo spool and boost torque output significantly.

Fuel Map

If starting from scratch, do as you would regularly by over doing the fuel and working backward. If starting with a fuel map that has already been mapped out for pump gas, calculate a 30% increase and apply it to the entire map. This will give you a good idea of wear to start. From here, tune the car just as you normally would. Most of the time a 30% increase will add more fuel than needed and the car will be overly rich. This is perfect as a safe starting point that you can then pull fuel from to tune the car safely.


Not only do most pump stations not pump an exact E85 mixture, they also will vary the mixture that they carry from summer to winter. Example: One local pump station here cares E90 all year round, while one just a few miles away cares E60 in the summer, and E70 in the winter. If tuning a vehicle TO THE LIMIT of its ability, be sure you know what your putting in the tank every time.


If you have access to E85 in your area and have a tunable ECU, then E-85 could be a GREAT alternative to race gas. Not only is it far cheaper, but for boosted applications its cooling properties are very desirable. As long as you follow the proper steps in upgrading the fuel system, and tuning the car properly, you will be hooked on this wonderful fuel.