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E85 Fuel Switch - How It Works

Thinking About Switching to E85? Here’s How it Stacks up to Gasoline, and Some Tips for Making an Easy Transition

Stephen Kim Aug 18, 2011
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Some forced-induction guys swear by the stuff, and it’s of the few things that both hot rodders and tree huggers can embrace. Farmers love how it fattens up their piggybanks, and lobbyists are working hard to spread its popularity by bribing lawmakers. We’re talking about ethanol, E85 fuel to be exact, and few topics are as polarizing in both consumer and enthusiast circles. We’re all about performance, so we’ll focus on the benefits of E85 instead. There are lots of them, but E85 comes with plenty of drawbacks as well.

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If there’s one universal truth when it comes to E85, it’s that there are a ton of misconceptions and urban mythology floating around out there. For example, E85 is said to have a much higher octane rating than regular pumps' gas, but did you know that the octane number for all ethanol fuel is pure bunk? Likewise, in instances where E85 does produce more power than gasoline, its higher octane number is rarely the reason why. What’s more, depending on the time of year when you fill up with E85, it might actually be E70. On the flip side of the equation, E85 and boost are often a match made in horsepower heaven, and it’s a heck of a lot cheaper than gasoline. To help us sort through all the mythology, we sought the expertise of Tim Wusz at Rockett Brand Racing Fuel. The company offers both high-octane gasoline and E85, so it has a good handle on the pros and cons of corn juice. Additionally, for advice on how to convert a gasoline fuel system and carb over for E85 use, we chatted with Marvin Benoit of Quick Fuel Technology. Here’s the scoop:

Octane Number

Tim Wusz: There is a lot of misinformation floating around regarding the virtues of ethanol and ethanol blends like E85 when compared to gasoline. Many hot rodders feel that E85 has a significant octane advantage over gasoline, but the truth isn’t so clear cut. In reality, it’s difficult to directly measure the octane rating of E85 because ethanol vaporizes at 172 degrees F. On the other hand, gasoline typically has a boiling range of 100 to 430 degrees F. The Motor Octane Number (MON) test method was originally designed for testing gasoline, and requires that the air/fuel mixture be at 300 degrees F when passing through an engine’s air intake system. Ethanol is completely vaporized at that temperature and cools the inlet charge significantly, which makes testing it very inconsistent. As a result, ethanol is normally tested in a 50/50 blend of a known-octane gasoline and ethanol. The octane number of that blend is then used in an algebraic calculation to determine the octane number of the ethanol. Results vary because of the known octane product used, and also because the test engine provides less consistent results when high volatility fuels like the aforementioned 50/50 mix are used in an engine not designed for this type of fuel. To make a long story short, ethanol octane numbers are calculated from results gathered in less than ideal operating conditions. That is why there are ranges for ethanol octane numbers posted in the E85 fuels that we offer.

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Horsepower Advantage?

Tim Wusz: In instances where E85 does indeed produce more horsepower in an engine than gasoline, the common assumption is that it is due to E85’s higher octane number. However, when the air/fuel ratios are correct for both fuels, E85 and normal street gasoline will usually make about the same amount of power. Sometimes E85 will have a slight horsepower advantage, but that’s due to E85’s superior cooling effect over gasoline as the fuel evaporates, not its higher octane number. Since E85 absorbs more heat than gasoline as it vaporizes, this effect cools the intake system and improves volumetric efficiency, which improves cylinder pressure and also improves power.

When a fuel vaporizes in an intake system, it has a cooling effect, and it just so happens that ethanol cools much more than gasoline. The cooling effect is referred to as the latent heat of vaporization and is expressed as Btu per pound. For ethanol, the number is 396 Btu per pound, and for gasoline that number is approximately 150 Btu per pound. As one can see, this is where the advantage is.

Cooling Effect

Marvin Benoit: In addition to the octane advantage of E85 over gasoline, since it’s an alcohol-type fuel, most motors will generally produce more torque on E85. In fact, we have local NHRA Super Street racers who have had great success running E85. For bracket racers, the lower cost of E85 makes it a great deal. Furthermore, motors will typically run 15-20 degrees cooler on E85 than gasoline. In some cases, that can be enough to solve overheating problems. Ultimately, you can put a bigger motor in a street car with E85 without having to worry about overheating, and have more horsepower thanks to the cooling effect of the alcohol content.

Air/Fuel Ratio

Tim Wusz: E85 requires a richer air/fuel mixture than gasoline because, ideally, we want to burn as much fuel as we can with the amount of oxygen in the air. With E85, additional oxygen is contained in the fuel itself so the mixture must be richer to burn all of the fuel and oxygen available. Pure ethanol contains 34.7 percent oxygen compared to most gasolines that contain between 0 and 3.5 percent. This means that more fuel can be burned when using greater amounts of ethanol. The reason that power does not continue to increase is because ethanol is much lower in energy content than gasoline. The Brake Specific Fuel Consumption numbers for E85 will be much higher than for gasoline because more pounds of ethanol are required to make comparable power numbers to gasoline. If you attempted to operate a carbureted engine on E85 without richening the mixture, the air/fuel ratio would be very lean and the engine would misfire along with having very poor driveability. Additionally, E85 contains approximately 82,000 Btu per gallon and pure gasoline with no ethanol in it contains approximately 115,000 Btu per gallon. This is why the air/fuel ratio for an E85 fuel must be much richer than for gasoline.

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E85 for Forced Induction

Tim Wusz: In many naturally aspirated street engines, E85 and gasoline will produce about the same horsepower. That said, many hot rodders have built forced-induction motors that run quite well on E85. In a forced-induction system, E85 is better than 91-octane street gasoline on a cost basis because of the increased cooling effect it provides in the induction system. Richer air/fuel mixtures contribute to a greater amount of cooling, which enhances power because it enhances volumetric efficiency. The estimated octane number for street blends of E85 is 105 using the (R+M)÷2 octane rating method. These numbers are optimistic because the quality of the 15 percent gasoline portion can vary significantly. Rockett Brand Racing E85 fuel will work much better than street E85 available at regular gas pumps because of its superior consistency from batch to batch. It’s important to note that at high boost levels, E85 will run out of octane quality to satisfy an engine’s operating conditions. That is where a high-quality, high-octane gasoline will outperform an E85 fuel.

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Is it E85 or E70?

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Tim Wusz: Consumers who fill up on E85 assume that it’s 85 percent ethanol, but depending on the time of year, that’s not always the case. Since ethanol requires more heat to vaporize than gasoline, modern flex fuel vehicles run into cold start problems when the ambient temperature drops below 20 degrees F. Consequently, during cold weather months the Federal Government allows up to a 30 percent gasoline content in E85, which really makes it E70, to ensure that cold starts are possible. This creates a new set of problems. While flex fuel vehicle with EFI can adapt to the different amounts of gasoline because of the feedback system that controls the air/fuel ratio, carbureted engines don’t have this luxury. As a result, small changes in the amount of ethanol content will cause air/fuel ratio changes that have a significant effect on vehicle driveability. As the amount of ethanol in the fuel is decreased, the mixture becomes richer. If the amount of ethanol was increased, the mixture would become leaner and eventually too lean. In either case, the carburetor would have to be re-jetted to obtain best performance.

Checking Ethanol Content

Marvin Benoit: One of the undesirable qualities of E85 is that it doesn’t light off as easily as gasoline in cold weather. What you think is E85 might actually be E70 in the winter, which requires different carburetor calibrations. To help you measure exactly what concentration of ethanol is in your fuel, Quick Fuel Technology offers an e-checker kit. It’s basically a test tube that you first fill with water, then with E85. Next, you shake it up, and as the ethanol separates from the gasoline, it will float to the top. Depending on which marked line the ethanol comes up to on the tube, it will tell you exactly how much ethanol content is in the fuel in question. From there, you can tune your carb accordingly.

Required Fuel System Mods

Tim Wusz: Since most cars aren’t designed to run on E85, their fuel systems must be modified to make them ethanol compatible. Ethanol is somewhat corrosive, but not as corrosive as methanol. To be on the safe side, we suggest to our E85 customers that they have a methanol compatible fuel system. This means that the fuel pump, fuel lines, injectors or carburetors, fuel tank, and fittings must be compatible with methanol to ensure that they will hold up to ethanol. Usually, anodized aluminum fittings are OK.

Cost Advantage

Tim Wusz: E85 is often cheaper at the pump than gasoline, but in many instances it might actually cost more to run E85 than gasoline. First off, there is a $0.51 per gallon subsidy contributed by the U.S. Federal Government to encourage people to use E85 in flex fuel vehicles, and any cars that have been converted to run on E85. Even when E85 fuel is less expensive than 87-octane gasoline, it is usually not cost effective to use E85 because the system must be calibrated to run approximately 40 percent richer based on the stoichiometric air/fuel ratio. Unless E85 is about two thirds the cost of gasoline, your fuel costs will be higher with E85.

Street vs. Race E85

Tim Wusz: All E85 fuels are not created equal, and as such, the quality can vary dramatically from one E85 blend to the next. Street E85 has just one restriction on the 15 percent non-ethanol portion that is used. That restriction states that the 15 percent non-ethanol content must be either gasoline or gasoline hydrocarbons. This is a very loose stipulation since the quality can vary tremendously from a good-quality gasoline to the cheapest hydrocarbon that the blender has available. In fact, it is actually very uncommon that a high-quality gasoline is used for that 15 percent. It gets even worse in winter months because the Federal Government allows the amount of ethanol in E85 to be adjusted so that flex fuel EFI vehicles will start at ambient temperatures below 20 degrees. During the winter, the ethanol level in E85 can legally be as low as 70 percent with the gasoline component being 30 percent. What this means is that during cold weather when the gasoline component is raised from 15-30 percent of the blend, the potential problem of poor quality doubles with the gasoline portion of the blend.

At Rockett Brand, we have found some E85 that contains less than 65 percent ethanol. This may be OK for flex fuel vehicles, but if a racer is trying to use what he thinks is E85 but the actual ethanol content is lower, his carburetor calibration can be overly rich. Samples taken with 90 percent ethanol have also been reported, which would make the carburetor calibration lean. The point here is that any deviation in ethanol content from the 85 percent standard for a carbureted race vehicle begins to introduce more variables for the racer. In contrast, Rockett Brand E85 is always blended to 85 percent ethanol with hand-selected blending components that comprise the other 15 percent of the blend. The components used have very good octane quality also. The benefit of this consistency is that the racer does not need to be concerned with recalibration of his carburetor every time he gets a fresh batch of Rockett Brand E85. Every batch is the same. Even though the racer must pay attention to weather and track variables, the fuel itself is not a variable. The bottom line is that Rockett Brand E85 is extremely consistent from batch to batch, and the 15 percent gasoline portion of the product contains high-octane gasoline blending stock.

E85 Carbs

Marvin Benoit: When running E85 in a street car, there are several modifications that need to be made to the carburetor. To make the transition from gasoline to E85 easier, Quick Fuel Technology offers carbs ranging from 650 to 1,250 cfm designed specifically for E85. Since E85 requires an air/fuel mixture that’s 30 percent richer than gasoline, we enlarge all the internal passages in our E85 carbs. By opening up the boosters and enlarging the metering block and main wells, we can achieve the necessary increase in fuel capacity. These changes allow you to run the same jet sizes as you would on gasoline, but at the correct air/fuel ratio for E85. Since E85 is more corrosive than gasoline, we use anodized aluminum parts in our E85 carbs as well. If you don’t modify a carburetor when switching over to E85, you can easily run out of jet size. On a carb designed for lower horsepower bracket racing motor, we offer a metering block kit with a modified needle-and-seat assembly and a special diaphragm that resists corrosion. These modifications will allow you to convert a regular gasoline carb over for E85 use. CHP


Quick Fuel Technology
Bowling Green, KY 42101
Rockett Brand Racing Fuel
Mount Prospect, IL



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