All across the United States, the cost of premium unleaded gasoline, the lifeblood of our high-performance engines, is approaching the $5 mark. Even the most resolved performance enthusiasts now at least consider for a moment the costs of fuel when the total tab for a fill-up approaches $60.
Not everyone gets the same performance for their money. Despite uniformly high fuel prices across the board, some regions get 93 or 94 octane fuel while other, less fortunate enthusiasts in California and the desert Southwest are bridled by poor-performing, lower-octane premium fuels. Higher octane means the engine can be tuned to a greater efficiency and power production because higher octane fuels are, by definition, more detonation resistant. Greater efficiency not only translates into better performance but also better fuel economy, as the engine is able to generate more mechanical force with optimized ignition timing and fueling strategies.
Turbocharged engines are particularly sensitive to overall fuel quality and detonation resistance. For example, an optimally-tuned Subaru STI running 94 octane fuel from Ohio will be able to generate 20 more wheel horsepower and torque than its mechanical twin located in the Los Angeles area, where 91 octane is the highest octane pump fuel available. Furthermore, the STI tuned to run on 91 octane will run a richer fuel mixture than the car fueled with Midwest 94 octane. The difference in "on boost" air-fuel ratio (AFR) can require as much as seven percent additional fuel to run safely on 91 octane.
High-Octane Alternatives: E85 and Methanol Injection
The most common strategy used to offset lower octane fuels is a combination of methanol and water injection. In a previous issue of Subiesport ("Tuning for Water and Methanol Injection", September 2007, p. 86) we reviewed in detail the tuning techniques, advantages and risks associated with water or water and methanol injection. However, there is a new fuel on the market in some parts of the country that now provides a very good alternative to methanol injection and has the advantage of actually lowering overall fuel costs. Properly calibrating a car to run on either methanol injection or E85 requires some form of aftermarket engine management as well as custom tuning on a dyno, so either approach requires a similar initial investment.
E85: Low-Cost, High-Octane
This new fuel is called E85. E85 is a blend of 15 percent gasoline and 85 percent ethanol. Yes, the same ethanol that you enjoy in alcoholic beverages is a viable fuel. Just like a gin and tonic, ethanol packs a punch in the form of a comparatively high octane rating of about 105. To top it all off, E85 is less expensive compared to premium unleaded fuels. According to the California Energy Commission, the average price of E85 in June of 2008 was $3.29, while the average price of premium unleaded was $4.29 per gallon. This represents nearly a 25 percent difference in price. Based upon this information alone you may be asking yourself, "Where can I get E85?" There are, however, many factors that mitigate the pure economic value of this fuel alternative.
Despite having a higher octane rating, E85 has a lower overall energy density than pure pump fuel. Pure gasoline contains approximately 125,000 BTUs per gallon, while E85 contains approximately 84,000. This means that a greater volume of E85 must be utilized to realize the same energy content. This lower hydrocarbon content is mirrored by the stoichiometry of E85 and pure unleaded gasoline. Complete combustion of pure gasoline requires 14.7 parts air (mixed gas air with 23 percent oxygen) with one part fuel. In contrast, complete combustion of E85 requires a much higher relative content of fuel with only 9.7 parts air required. The distillation of this information means that larger volumes of E85 are required for equivalent combustion when compared to pure pump fuel. Thus, the cost savings associated with lower E85 prices is offset by an overall reduction in fuel economy.
Turbocharged engines are particularly sensitive to overall fuel quality and detonation resistance. For example, an optimally-tuned Subaru STI running 94 octane fuel from Ohio will be able to generate 20 more wheel horsepower and torque than its mechanical twin located in the Los Angeles area, where 91 octane is the highest octane pump fuel available. Furthermore, the STI tuned to run on 91 octane will run a richer fuel mixture than the car fueled with Midwest 94 octane. The difference in "on boost" air-fuel ratio (AFR) can require as much as seven percent additional fuel to run safely on 91 octane.
High-Octane Alternatives: E85 and Methanol Injection
The most common strategy used to offset lower octane fuels is a combination of methanol and water injection. In a previous issue of Subiesport ("Tuning for Water and Methanol Injection", September 2007, p. 86) we reviewed in detail the tuning techniques, advantages and risks associated with water or water and methanol injection. However, there is a new fuel on the market in some parts of the country that now provides a very good alternative to methanol injection and has the advantage of actually lowering overall fuel costs. Properly calibrating a car to run on either methanol injection or E85 requires some form of aftermarket engine management as well as custom tuning on a dyno, so either approach requires a similar initial investment.
E85: Low-Cost, High-Octane
This new fuel is called E85. E85 is a blend of 15 percent gasoline and 85 percent ethanol. Yes, the same ethanol that you enjoy in alcoholic beverages is a viable fuel. Just like a gin and tonic, ethanol packs a punch in the form of a comparatively high octane rating of about 105. To top it all off, E85 is less expensive compared to premium unleaded fuels. According to the California Energy Commission, the average price of E85 in June of 2008 was $3.29, while the average price of premium unleaded was $4.29 per gallon. This represents nearly a 25 percent difference in price. Based upon this information alone you may be asking yourself, "Where can I get E85?" There are, however, many factors that mitigate the pure economic value of this fuel alternative.
Despite having a higher octane rating, E85 has a lower overall energy density than pure pump fuel. Pure gasoline contains approximately 125,000 BTUs per gallon, while E85 contains approximately 84,000. This means that a greater volume of E85 must be utilized to realize the same energy content. This lower hydrocarbon content is mirrored by the stoichiometry of E85 and pure unleaded gasoline. Complete combustion of pure gasoline requires 14.7 parts air (mixed gas air with 23 percent oxygen) with one part fuel. In contrast, complete combustion of E85 requires a much higher relative content of fuel with only 9.7 parts air required. The distillation of this information means that larger volumes of E85 are required for equivalent combustion when compared to pure pump fuel. Thus, the cost savings associated with lower E85 prices is offset by an overall reduction in fuel economy.
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