E85 & Flex-Fuel

What is E85?

E85 is a type of fuel that consists of 85% ethanol and 15% normal petrol. As motoring enthusiasts we like this fuel for several reasons:

  • It is more environmentally friendly – E85 is a bio fuel as opposed to a fossil fuel, it is often made from crops such as corn or sugarcane and is a renewable energy source. E85 is also considered to have less harmful exhaust emissions than petrol.
  • It makes your engine more powerful – E85 produces more power and torque than petrol. Engines tuned to run E85 will produce 15-20% more power and torque.
  • Even though E85 makes more power, and puts engine parts under a little more load, the cooler burning fuel has a higher octane rating and is less prone to detonation. This is particularly important in turbocharged engines where piston failure can lead to expensive repair bills.

What is Flex Fuel?

Flex fuel vehicles can run on E85, normal 98-octane petrol or any mixture of the two. This really is the best of both worlds; combining the availability of normal petrol with the added power of the ethanol for a motorsport event or track day. Additional hardware is required for a flex fuel setup – typically a fuel system upgrade (injectors, fuel pump and hoses), an ethanol content analyser and either an aftermarket ECU or a modified program for the stock ECU. Vehicles are tuned first on normal petrol and then the fuel is changed to E85. The E85 tuning is then carried out before blending fuel at different mixtures to check correct operation.

At Tokyo Motorsports flex fuel is available for:

  • Any vehicle using a Link G4+ ECU: This uses a modelled multi-fuel equation allowing a seamless interpolation between the two fuels based on the output of the ethanol content analyser.
  • Any Subaru tuned with ECUTEK 2005 onward with drive by wire throttle. This uses one of the ECUTEK RaceROM features that allows the output of the ethanol content analyser to replace the rear oxygen sensor input to the ECU. Several tables then modify the petrol tune to allow additional fuel and ignition timing giving a seamless interpolation between the two fuels.
  • Any BRZ/FT86 tuned with ECUTEK. This works in the same way as the Subaru system, as above.
  • Any Evo 10 upgraded and tuned using the Tephra v3 open source ROM. This has two separate tunes (one for E85 and one for normal petrol); the output of the ethanol content analyser then drives several additional tables allowing the ECU to interpolate between the two.



The power graph showing the difference between a Supercharged BRZ running on BP98 and the same car running a flex fuel setup at approximately 80% ethanol content. Power is increased by 30Kw and torque by 40-50Nm across the rev range.


The power graph shows the difference between a 2008 WRX (fitted with a VF52 turbo + bolts on mods) running BP98 and the same car running a flex fuel setup at approximately 80% ethanol content. Power is increased by 30Kw and torque by 30-40Nm across the rev range with no increase in boost pressure.