Running E85 On Your Mazdaspeed

The Mazdaspeed 3 and 6 have been on the market since 2005 in the UK, Australia, and Japan, and since 2006 in the US and Canada. We are finally tapping in to the full potential that they have to offer. One of the ways we can tap that potential is through running E85 fuel. So whether you are daily driving a weekend warrior or building an all-out track monster, here is what you need to know about running ethanol in your direct injected Mazda.

Lets take a step back…

Don’t jump down the rabbit hole of E85 head first and go fill your tank expecting to make more power. It’s not that simple.  First, there is something you need to know about E85. It actually has a lower thermal energy rating (BTU) than gasoline. The reason it makes more power than gasoline is because of this deceptively low rating. Since it has less energy per molecule, you have to stuff a lot more molecules of ethanol into the cylinder to reach a stoichiometric burn, about 30% more to be precise.  With all those extra molecules, the average BTU ends up being higher than that of gasoline and therefore you can make more power.

Because of this, you will lose power if you can’t get more fuel in the cylinders. Therefore, the ability to tune is hugely important. Enter the Cobb Accessport. With the Cobb AP, you will be able to adjust your fuel accordingly in order to make more power with E85.

However there is still one more speed bump in the way. The dreaded HPFP internals. Without an upgraded high pressure fuel pump, you will run into fueling issues quick so it is highly recommended to upgrade before running E85. Either the CP-E replacement pump or some good ol’ Autotechs will do the job and get you staged for a big time power boost.

Now we can move forward…

Now that you have the necessary parts to begin your E85 journey, you need to decide exactly what that journey entails. Since E85 requires tuning, what all needs to be tuned? The answer to that question is quite simple, fuel and ignition timing.

We’ve already established that you need more fuel, so how do you get more fuel? You need to tell the car. A Protuner or an E-Tuner is the best option for this and you can find some highly recommended ECU tuners on our site.

Why more fuel?

Because Ethanol is less energetic, you will need to get more of it in the cylinder. Even if you are doing a light mix of E85, you will need to be able to get more into the cylinder.

Why more spark advance?

Ethanol burns slower and more controlled than gasoline and this is part of the reason we love it. This slower burn is more controlled and more resistant to detonation and allows you to make more power safely. But because it burns slower, you have to start the burn sooner in order to achieve peak cylinder pressure at the desired 15ish degrees after top dead center (ATDC). Reach peak cylinder pressure at this point is where the max brake torque (MBT) occurs and provides the best and most efficient power. In order to get the ignition spark to light off the fuel and air mixture at the right time, you need to advance the ignition timing through tuning.

To mix or not to mix, that is the question…

With a direct injection car like the Mazdaspeed 3 and 6, you have to be careful about running full E85 as the car was not intended to. Ask any of the OG’s in the platform about black death and you’ll learn real quick why it isn’t the best idea.

The “black death” is, as far as we understand, the result of ethanol mixing with oil at the High Pressure Fuel Pump (HPFP), and the oil breaking down as a result causing the HPFP to fail. This can be resolved by only running a mixture no greater than 50% E85 to 50% regular gasoline.

"Black Death" from internal component of a Mazdaspeed
high pressure fuel pump.  Photo courtesy of Mazdaspeedforums.org

While it is a pain at the pump to mix the two fuels, the results are very positive. You don’t have to break down and clean out your HPFP every month, while also gaining enough octane through the E85 to achieve MBT. This will get you loads of extra power for the cost of a little tuning.

However, there are some other issues you may run into. The Mazdaspeeds are direct injection with no fuel volume upgrades available through larger injectors.  So if you are running a bigger turbo and using the stock fuel system, which everyone is, you have to be careful how much E85 you use. As ethanol content goes up so does fuel demand and you are already limited with a larger turbo.  A small enough mixture to get you past the knock limit will suffice to increase power without overly increasing demand on the fuel system. Here is where it is important to find the balance point so you don’t run too lean. Typically, a 3 to 4 gallon mix of E85 will be all that is needed.

One last major curveball is the true ethanol content of E85 at the pump.  During the winter months, it’s extremely common for the fuel companies to blend less than 85% ethanol into the fuel.  Some pumps see as little as 60-70% ethanol even though it’s advertised as 85%.  So if you’re putting 4 gallons of E85 in your tank at every fillup, you might not be putting the exact same amount of ethanol in your tank depending on the time of year.  It is wise to use the same brand of gas and test the ethanol content in it from time to time with a simple ethanol content tester/analyzer.  This will allow you to know what is going in your tank and allow you to adjust your tuning needs accordingly. 

Direct Benefits

Running E85 and tuning properly for it will directly benefit you with more horsepower and torque throughout the entire powerband. You will notice better throttle response and faster turbo spool as well. Don’t be too disappointed in the slightly reduced fuel mileage, because, well you know… Because racecar!