Bio-Energy Series: Converting Gasoline Engines to Ethanol


by Randy Price


            Alternative fuels are becoming more important as gas prices rise and petroleum resources dwindle. This resource is especially important to farmers who drive many miles between fields, parts stores, and town. Although many farm vehicles are diesel (and you should be looking at bio-diesel for those), quite a few farmers still have gasoline vehicles (cars, trucks, tractors) and you are left with the option of what to do with these vehicles?

If you are lucky enough to be at the end of your automobiles or trucks economic depreciation cycle and you are considering buying a new car or truck, then it is very likely you will find and be able to purchase a FFV (or flex fuel vehicle) that is equipped to run on any alcohol based fuel up to E85 (fuel with 85% ethanol[1], the E number stands for ethanol and the number after that indicate the percentage of ethanol in the fuel). If not, you are left with the option of either buying a new car before you are ready, or burning the higher cost fossil fuels. Still, there are some options arriving on the market place that may help you out.  These options are conversion kits that may allow you to convert your vehicle to E85.  These kits may even be useable on gasoline powered tractors and other engines with the correct modifications.

The main factor in converting a regular fossil fuel engine into flex fuel engine is to get the fuel mixture correct. Ethanol contains roughly 30% less BTU’s than regular fuel and requires more fuel to be injected into the engine to get the right stoichiometric conditions. Stoichiometric ratio is the proper ratio of the air to fuel ratio to cause complete combustion. A normal car will run this mixture slightly rich to get the best mileage with least amount of engine wear (an engine running above this ratio will overheat and ruin the internal combustion parts).  The correct stoichiometric ratio for regular unleaded gasoline is 14.7:1, while 9.7:1 for E85 (and can be any value in-between for different alcohol/fuel ratios). In newer cars, this means either holding the injectors open longer to get extra fuel into the engine, or running a higher flow rate injector. In carbureted engines, this means re-jetting for a higher flow rates. Newer flex fuel cars are already designed for these large changes in flow conditions and can automatically re-jet for the various fuel/alcohol ratios (they usually use the exhaust O2 sensor and various other sensors to determine the correct fuel to air ratio mixture).  In older cars (even ones with injection systems as late as last year), the computer box and injectors cannot hold the injectors open long enough to get a rich this mixture with the E85 fuel. In Brazil and other countries, this problem has been circumvented by using a special box that plugs in-between the computer and the injectors, and causes the injectors to be held open longer (Figure 2). You could also install a larger set of injectors, but the vehicle might not run correctly on regular fuel.

Another concern with running E85 is to make sure all the fuel system components can tolerate the alcohol fuel. Alcohol is a strong cleaning agent and has the ability to degrade certain engine parts, such as natural rubber, plastics, and even metals, over time. A list of material affect by E85 can be found at the Alternate Fuels and Advanced Data Base Center -

Currently, all cars dating back from around 1994 (and most cars as far back as 1985/86) have fuel systems that can handle alcohol fuels.  At that time, alcohol was considered as a replacement for MTBE (methyl tertiary-butyl ether), an additive to used to raise the octane level and oxygenate fuels for complete burning, and most manufacturers were required to sell vehicles that could operate with alcohol. Still, some care must be taken to make sure all the fuel system and components are rated for alcohol fuels (this even means the fuel tank and other areas where fuel may contact – lines, hoses, injectors, etc.). The main concern is natural rubber parts, which must be replaced with synthetic rubber parts (luckily most hoses sold today at the local parts dealer are synthetic!) and the fuel tank, which should not be made of aluminum. Metal tanks, although safe for alcohol, may corrode and leak from the cleaning action of the alcohol fuel) and need to be replaced. If the tank is metal, you should either clean the tank (by having it vatted at a local machine shop to insure that there are no leaks), buy a new plastic tank, or get the inside coated with an alcohol tolerant coating. Another concern is that many of the impurities (carbon, gum, dirt, etc.) which cause the brownish tint on tanks and other parts will dissolved in alcohol fuels and be cleaned off, end up in either the fuel filter or the injectors (which sometimes causes clogging – several people have reported this!).  

In any E85 conversion you can expect to lose from a 2 to 30% in mileage (sinceE85 has less BTU’s than gasoline), but many FFV are only losing about 2 to 10%. Note Figure 1 where a Flex Fuel car was run on E85 and only saw a 5% reduction mileage.  In fact, for this car more mileage was lost due to driving speed and habit. At 78 MPH the car got 26 MPG and at 60 MPH it got 33 MPG giving a 25% increase in mileage!



















Figure 1: Car mileage on pump gas (87 octane regular unleaded) and E85.


If mileage is a concern, there are ways to get it back. The octane rating of ethanol is much higher than gasoline and typical resides in the 100 to 105 range, thus the compression ratio of an engine can be raised without fear of detonation (a symptom where multiple flame fronts appear during ignition and the collisions cause high mechanical stresses on engine parts) and more power can be achieved from the engine. Most manufacturers design engines for an 8:1 to 10:1 compression ratio, but in ethanol this ratio can be increased to 12:1 to 14:1. This property may lend itself well to super or turbo charged engines, where the compression can be raised by merely changing a pulley or impeller (to cause a higher boost ratios). Another method is to “mill-the-head”, lowered it closer to the piston (and reducing the clearance volume) but this requires major engine modifications and may preclude the engine from running on regular fuels.

In the U.S., the conversion box (Figure 2: plug in-between the injectors) is currently not allowed because law states that fuel systems cannot be modified from the original manufacturers specifications. Also, they must undergo strict emission testing to get a certificate for use on public highways (current fuel injector systems are sold as an off-road use system only). Still, there is one system has been certified for use on certain cars in the U.S. on public highways. This is the Flex Fuel U.S. system which uses a bolt-on injector plate (like nitrous oxide injection systems) and adds supplemental fuel through an injector in this plate (like throttle body fuel injection systems). The system contains an alcohol sensor to tell the flex fuel computer what ratio of alcohol you have in the fuel and then makes appropriate adjustments. Since the system does not involve your OEM fuel system (or change it), the system is considered an accessory add-on and meets U.S. certification. EPA testing with the units has also indicated that exhaust gases exceed original manufacturer’s ratings.

This system may also be useable on older carbureted gasoline engines (such as those found on older tractors and other agricultural engines) since the system adds fuel through a separate injector plate. In this case, a separate fuel pump (rated for fuel injection pressures – Figure 3), supply line, and return line are installed on the tank and run to the flex fuel system.  An injector installed between the carburetor and manifold supplies extra fuel. No other modifications are necessary. Even the original jetting of the carburetor is left the same. The only caution is to make sure the fuel system components (carburetor, fuel lines, fittings, tank, etc.) are E85 compliant. If the engine is run on regular gasoline, the flex fuel system will turn itself off and regular gasoline fuels can be run through the engine at any time. If you are worried about the system running too lean, you can install an O2 sensor (available at most parts stores) in the exhaust pipe and monitor fuel mixture conditions. 


































Figure 2: Typical Injector PWM Systems.










Figure 3: Typical inline fuel pump.


In colder climates, starting may be a concerned. Alcohol contains much less explosion potential and heating point, which prevents it from exploding well in a sub-freezing engine. Potential solutions to this are block and radiator heaters, running regular fuels during this time, starter fluid, raising the compression of the engine (to aid in explosion) or having a separate fuel tank with regular gas (and a switching valve).

If you decide to convert a gasoline engine to ethanol, consult a licensed professional who can help you evaluate the changes that will needed to the engine and hire a licensed d person or mechanic to do the modifications for you.




Alternative Fuels and Advanced Fuel Resources Center:



Abcesso Technology


Abcesso Exp/Imp. Ltda

Av. Alfredo Baltazar da Silvera 580 
Recreio dos Bandeirantes, loja 271
22790-710 RJ - Rio de Janeiro


Tel: + 55 21 3521-7216

Skype: abcesso



Fuel Flex International, LLC

Ph: 866-568-3617



Flex Fuel U.S.:


5820 N. Northwest Highway

Chicago, IL. 60631

Ph: 773 / 763 - 7900

Fax: 773 / 763 – 0878


Rochester Products

250 Mill Street

Rochester, NY 14614

Ph: 585-777-4030



White Lighting: Ethanol Conversion Systems:

White Lightning LLC
2941 Main Street; Suite F
Santa Monica, California 90405





Check List:


The following factors should be considered before attempting to convert an engine over to ethanol:


-         Can the fuel system support alcohols?

o       Are the rubber components alcohol friendly?

o       Is the tank made out of a material that can support alcohol?

§         Get a metal tank cleaned and possibly coated

§         You may need to switch to a plastic tank

§         Most new cars have plastic tanks that will work and can be acquired a junk yards, etc.

o       Can the rest of the system support alcohol?

















[1] Ethanol is alcohol based fuel made by the fermentation of corn starch, sugars, and other resources.  This is the predominant alcohol fuel used today and mixed with regular fossil fuel gasoline (although other versions exist such as methanol, butanol, etc.).