General Concept:

The E85 calculator helps you design your E85 fuel conversion. There are at least three applicable aspects to doing an E85 conversion and the calculator does all three superbly:

1- Upsizing your fuel delivery system to allow for the higher volumetric flow rate required to run Ethanol or E85 for the same power level (compared to gasoline).

2- The ability to run higher static compression ratios due to the higher octane capacity of an alcoholic fuel.

3- The lowered boost requirement to reach your power goal (for turbocharged and supercharged cars) due to the increased latent energy stored in Ethanol compared to gasoline (Which means you will make more horsepower per the same amount of airflow which is great when you have a setup where your rpm range, boost range, or some aspect of your engine design is already maxed out- yet your are still looking to find a little more power out of your current combination).

The article below details the process of how our horsepower calculator and more specifically the E85 calculator module in the power calculator works:


I had a question over email the other day about an E85 converted, supercharged BMW 3-Series. After answering the question, I thought it would be helpful and interesting to demonstrate to all my readers here and followers (on facebook and twitter) the advantage of using E85 on a supercharged set-up and the possibilities it opens up during your build up.

As an introduction, E85 is an alcoholic fuel that is 85% Ethanol and 15% Gasoline. E85 is a high octane fuel with an Octane rating of around 102 Octane points which, when compared to gasoline and it’s 92 Octane points rating, has an additional 10 points of Octane.


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The advantage of using a higher octane fuel is that the in-cylinder flame front travel rate of a higher octane mixture is slower than that of a lower octane mixture. If you had watched my video series on tuning your timing and timing trends (here), then you may remember that the flame front travel speed is affected by many factors including mixture density and in cylinder pressure.

Having a higher octane mixture, slows down the burn rate. This means that we can increase our boost level, our compression ratio, or our timing advance and return the mixture to a normal burn rate similar to that of gasoline, having a similar level of ‘safety’ in the cylinder, a similar mixture volatility, but albeit at a higher power level.

To put some exact figures to this phenomenon, switching from 92 Octane premium gasoline to 102 Octane E85 allows you ONE of the following options:

  • Increasing your boost level by 6psi of boost above your gasoline maximum boost level.
  • Increasing your static compression ratio by 2.5 compression points above your gasoline maximum safe compression level.
  • Increasing your timing advance by 13 degrees of timing above what you would use for a gasoline tune.

(Or some combination of the three such as a 3psi boost increase with a 1 point compression hike, resulting in a similar overall increase in compression pressure and flame front travel speed).

Now the advantage of this high octane feature of E85 is that it allows you to build a more aggressive set-up, to reach a higher power goal, while having a similar margin of safety to that of gasoline. The real world benefit of this kind of set-up, is that you have two new possibilities opening up for you in your power build:

  1. You can now reach higher power goals, on E85 at the same red-line, and with the same static compression ratio, by being able to run more boost on the same motor, safely.
  2. You can now build high compression supercharged set-ups, because you will no longer need to take apart your engine to replace your pistons, to lower your compression ratio, or severely retard your timing to be able to boost a factory high compression motor.

The second interesting fact about E85 ethanol based fuels is that it reaches stoichiometry at an air:fuel ratio of 9.7:1 compared to an air:fuel ratio of 14.7:1 for gasoline.


By dividing those two figures into each-other it becomes apparent that an engine running on E85 needs 48% more fuel flow compared to the exact same engine running on Gasoline. For example, a 400hp 6 cylinder engine will require about 400cc/min injectors for a gasoline setup, but it would need almost 600cc/min injectors to be converted to Ethanol.

The advantage of this information, is that a car that is built to run on E85, has enough injector to also run on gasoline. The benefit of this kind of set-up is that having a dual-map ECU, with large injectors designed for E85, can be ‘detuned’ to reduce it’s injector duty cycle by 48% to run on gasoline. This is essentially how ‘flex fuel’ cars are mapped to run on either fuel, namely because their factory fuel system is oversized (for gasoline) allowing them to run either E85 or Gasoline.

The third interesting fact about E85 is that it has a LOWER energy output than gasoline.

E85 has can produce 25.2 Mega Joules of Energy per Liter of fuel, while Gasoline can produce a more potent 33.7 Mega Joules of Energy per Liter.

Your first thought, might be that gasoline is thus able to produce about 30% more horsepower on the same engine (because gasoline is a more potent fuel chemically speaking), however when you factor in that we are injecting 48% more fuel with E85 to reach a complete combustion and stoichiometery, then the net result of those two figures is that E85 has the potential to deliver 11% more horsepower on the same exact engine, when compared to Gaslone.

This 11% boost in power, is based on a straight gasoline to E85 conversion. More power can be found using E85 by taking advantage of the higher octane rating and tuning specifically for E85 or adding more boost and compression into the mix.

The advantage of this 11% power boost is that you can make more power with the same amount of airflow. The benefit here, is that if you have an engine that is maxed out at say 450hp because that is the maximum amount of air your supercharger can flow, you can add in another 11% (or 50hp!) by converting from gasoline to E85, without having to upgrade your airflow side of the equation (blower included).

So to illustrate how you can use the Power Calculator to plan your E85 fuel conversion, I have prepared a short video showing the process. This video includes 3 main differences from using the calculator for a gasoline setup as follows:

  1. The target power level you enter into the power calculator should be 11% lower than your actual power level. For example, if you are shooting for 450hp, then entering a target of 450/1.11 = 405hp will give you the right airflow side of the equation, including your intake, exhaust, and supercharger systems.
  2. Once the calculator has given you the results of your airflow side of your build-up as described in step #1, you can add 2.5points of compression ratio to your maximum safe compression level. That is to say, that if the calculator recommends an 8:1 compression level as the maximum static compression ratio, then on E85, you can run up to 8+2.5 = 10.5:1 points of static compression and still have a safe set-up.This makes E85 an amazing option for supercharging cars that come from the factory with a higher compression ratio such as 10.5:1 or higher because E85 will allow you to boost this engine WITHOUT the need to take the engine apart and lower the compression ratio.
  3. To calculate your fuel demands on E85, you need to inflate your power target by 48% as we explained earlier. So shooting for the same 450hp target, we should enter a target of 405*1.48 = 600hp to the calculator to give us the correct injector, fuel pump, and fuel line sizing for an E85 build-up.

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Example application:


A great example of an Ethanol conversion is the new Tri-Fuel Lotus Exige. The exige is a true Tri-Fuel care capable of running on Gasoline, Ethanol, or Methanol.

The only modifications performed to the car as per the official lotus press release are:

  • Sensors to detect alcohol content
  • Slightly modified software for engine management controls/ECU’s over ethanol/gasoline and flex fuel
  • Fuel lines compatible with alcohol
  • Higher flow rate fuel pump and injectors
  • Fuel tank material, compatible with alcohol

Making no changes to the airflow side of the engine, lotus is able to coax out an extra 51 hp or 19% more power from the same power plant simply by switching to an 11% more potent fuel mixture (as we mentioned earlier) coupled with another 8% coaxed through an alcohol specific tune with more aggressive mapping to take advantage of the higher octane and slower burn rate properties of alcoholic fuels.

Use the power calculator to design your E85 conversion

Special offer: Tweet this article to download chapter 1 of
The Tuner Mastermind (our best selling tuning guide) for free
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