Ethanol has long been used in racing because of its desirable properties for increasing engine power output. E85, too, increases the power and torque capa­bility of engines compared with gasoline. Most spark-ignited engines used in on­road vehicles operate with air to fuel mixtures at or near the stoichiometric condition. Since the stoichiometric air to fuel ratio of E85 is less than gasoline, engines operating on E85 can use about 1.48 times more E85 for the same amount of air. Remembering that about 1.4 times more E85 is required to equal the energy of gasoline on a volume basis, this leads to about a 6-7% increase in power.

Since E85 burns cleaner and the engine spark timing can be advanced due to the increased octane number, an engine operating on E85 can actually achieve higher increases in power.

Additionally, E85 has a higher heat of vaporization than gasoline. This is important in spark-ignited engines as the fuel is inducted into the intake manifold. As the fuel vaporizes due to the heat of the engine, it displaces air, reducing the ability of the engine to draw in fresh air. This reduces the volumetric efficiency of the engine, reducing the power. By increasing the heat of vaporization, E85 increases the engine volumetric efficiency, allowing more air to be drawn into the engine. This additional air allows the engine to use additional fuel, leading to increased power.

Further, an engine can be designed with a higher compression ratio to take full advantage of the increased octane of E85. All of these factors can be combined to increase power by more than 25% compared with the same-sized gasoline engine.