levels than gasoline engines achieve. Mileage is dependent upon the composition of the ethanol-gasoline blend, transmission, state of engine tune (primarily fuel-air mixture, spark timing and compression ratio). In the United States to offset this difference in fuel consumption in vehicles not optimised for ethanol, legislation has been passed to subsidize its cost. Energy value In contrast, ethanol critics contest the benefits of E85 by focusing on the fact that E85 has 33% lower heating value compared to the higher heating value of gasoline. However comparing energy expressed as a value of heat does not reflect the total work from an Otto Cycle. Because energy content does not factor certain latent or specific heat values, nor combustion pressure, looking at heat alone in the combustion equation does not determine efficiency or work according to the laws of thermodynamics. Octane and performance Use in flexible-fuel vehicles E85 ethanol is used in engines modified to accept higher concentrations of ethanol. In the US such FFVs are designed to run on any mixture of gasoline or ethanol up to 85% ethanol, whereas in countries such as Brazil where the climate is typically warmer, FFV run on neat alcohol. There are a few major differences between FFVs and non-FFVs. One is the elimination of bare magnesium, aluminum, and rubber parts in the fuel system. Fuel injection control systems have a wider range of pulse widths to inject up to 34% more fuel (which in turn produces more power). Stainless steel fuel lines, sometimes lined with plastic, and stainless-steel fuel tanks in place of terne (tinplate) fuel tanks have been used. In some cases, FFVs use specific engine oil that neutralises acidity. For vehicles with in-tank-mounted fuel pumps, precautions to prevent arcing, as well as flame arrestors positioned in the tank's fill pipe, are sometimes used. Octane rating As more effort is put into maximizing an engine to take advantage of E85's higher octane rating, engines achieve greater power advantages. One car that has higher power on ethanol is the Koenigsegg CCXR, which on ethanol is the fifth-most powerful production car, with 20% more horsepower on E85 than on gasoline. According to the manufacturer, this is due to the cooling properties of ethanol. E85 has an octane rating higher than that of regular gasoline's typical rating of 87, or premium gasoline's 91-93. This allows it to be used in higher-compression engines, which tend to produce