Gasoline is a complex mixture of different hydrocarbons, with a wide spectrum of constituents. Surrogate fuels have a reduced number of chemical components and therefore are used to model commercial fuels and enhance the understanding of fuel behavior in internal combustion engines. Surrogates also allow better fuel property control. In previous work, a surrogate fuel blend of iso-octane, n-heptane, toluene and ethanol was found to be suitable for commercial, high-octane, oxygenated Brazilian gasoline. This article investigates the influence on a Flex-fuel engine power and efficiencies of different ethanol levels in this surrogate fuel blend. The study found some different trends when comparing to other works in the literature. This article intends to make contributions presenting more detailed analyses of how fuel properties can influence several Flex-fuel engine performance parameters.