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E85 and what you need to know about flex fuel

Created on Wednesday, 09 January 2013 18:01


Over the last several years, we've been tuning more and more E85 powered cars for both the street and race track.  E85 has a number of benefits and we are going to review them, as well as compare them to pump gas, conventional race gas, and methanol injection.

The first thing you need to know about E85 is it makes tremendous power.  Without getting into the chemistry of it all, here are the basics:  It runs cooler than regular pump gas or race gas.  It burns cleaner and you get less soot out of your tail pipe.  It cools down the air charge (air going into your cylinder) because of its evaporative properties and the fact that about 30% more fuel is injected to maintain the same air fuel as with gasoline. That extra volume also make turbocharged cars build their torque and spool quicker; often about 500RPM quicker!  Lastly, and most importantly, people argue about the effective octane of E85, but the answer is right there on the dyno sheet.  E85 makes very similar power to C16 or 117octane fuels safely!


So to review:  E85 makes the same power and allows the same boost and aggressive timing just like race gas.  It costs less, spools quicker, and runs the engine cooler.

Pump gas has us very limited on turbocharged and high compression cars.  The low effective octane of pump gas means that we can't run much boost or timing before detonation occurs.  A higher octane fuel (such as E85 octane or 117 octane) resists detonation so you can run more boost or more timing and make more power without hurting the engine.

Methanol injection is one way to add more octane, but we find it generally tunes similar to 100 octane, so while it is a big help, it makes nowhere near the power of E85.  It also requires the addition of a methanol injection system, and some are much better than others.  We'll discuss methanol injection more in a future article.  Just know that methanol injection leaves a lot of power on the table compared to E85.

The main reason many shops and tuning companies have not pushed E85 is because they do not have a flex fuel ECU solution that supports automatic tuning with any variation of pump gas or Ethanol.  For example, the stock ECU of any non flex fuel car was designed to run on gasoline and therefore does not have the equipment or logic to understand ethanol content and make the tuning changes necessary to run the car with E85.  Sure, you can, we and do tune some stock ECU's to run on E85, such as a Subaru with a Cobb Accessport.  However, the customer must run E85 all the time or switch maps when switching fuel.  Since ethanol content varies depending on the station, time of year, etc, the tune will be inaccurate if we tune it on E85 and the customer happens to fill up at a station pumping E70.  The gas station does not need to advertise their ethanol content, and it varies wildly.

Our customers do not want to plug in a laptop and load in a different tune depending on their ethanol content.  They don't want to worry about forgetting to turn down their boost controller because they're running pump gas instead of E85, which will blow their motor.  Our customers want an ECU solution that does everything by itself.

Both the ProEFI 128 and Infinity ECU for their applications offer this.  Say a car makes 500whp on pump gas and 1000whp on E85, which is a very real possibility and demonstrates the potential power of E85.  For pump gas we'd be running 20 psi and on E85 we'd be running 30psi.  So say this customer is driving around on pump gas on a day to day basis.  He wants to go for a night out on the streets of Mexico so he drives over to the E85 station and fills up with E85 which is $18/gal less expensive than race gas.  Now he has E85 in the tank instead of pump gas.  The computer will automatically turn his boost up to 30psi, adjust his timing maps to the aggressive E85 timing maps, and adjust his fuel delivery according to the E85's different stoichometric value.  Just like that, his car is set to 1000whp before he gets out of the gas station parking lot.

Now, say that same customer is done having fun in Mexico and has used up 1/2 of his E85 tank.  He stops at another gas station to grab a drink and decides to top off the tank with pump gas.  So he has a 1/2 tank of E85 and a 1/2 tank of pump fuel.  His ECU will detect the change, set his boost to 25psi, adjust his timing maps to blend between the pump gas and E85 timing maps, and will adjust the fuel delivery to account for the ethanol content.  He will be running about 750whp, which is halfway between his pump gas and E85 tunes.  This is all done automatically; no switches, no buttons, no boost controllers, and certainly  no laptops.

How is this done?  Easy, we install a flex fuel sender which detects the amount of ethanol in the fuel rail.  In real time, this flex fuel sender (which is an OEM parts) tells the ECU what the ethanol content is so it can make the above changes real time and without any tuners' help.

Things you also need to know:

E85 requires about 30% more fuel by volume to make the same horsepower.  That means we upsize injectors, pumps, and lines accordingly.  All of our fuel systems that are E85 compatible have taken that into consideration.  So if you buy your turbo kit, fuel system, and ECU from us, they're all designed to work together.

Some injectors aren't happy on E85.  The injectors we sell will work with E85.  Call for application specific help.

Your E85 fuel system will be more expensive because it needs bigger components.  However, if you consider the costs of filling the average sports car up with C16, you'd only need to fill up about 6 times to cover the cost increase of an E85 fuel system.  From there on out, you'll enjoy $3.xx per gallon E85 with racegas or better performance.

Your exhaust system can't be undersized:  we've seen E85 make a restrictive exhaust more restrictive.  In order to get the maximum torque and spool up benefits E85 has to offer, it needs to breath.

E85 has a different air fuel and stoich ratio than gasoline. That means that it is best to tune using lambda, just like a stock ECU.  Both fuels like similar lambda ratio's for target horsepower, but the actual air fuel of each is different.

Be wary of any tuner/vender who tries to run E85 with out a flex fuel based computer.  We have done it before, and it works, but for an every day street car, you want flex fuel.  The options we offer that have very sophisticated and capable flex fuel systems are the ProEFI and Infinity ECU's.  Both are excellent options.

Here's is an excellent video that ProEFI and Saad put together on the flex fuel working on the 128 ECU in a Supra.  It works the same way in other applications.