The first production ethanol (E100) fueled capable vehicle was launched in Brazil in 1979. In the decade of 1980, most of the vehicles in Brazilian market ran either on gasohol (E22) or on ethanol. By this time, two different engine hardware had been developed: one for gasohol and one for ethanol, the latter with a higher compression ratio assuring a better fuel conversion efficiency. In this period, it was usual to have same vehicle models operating with an E100 / E22 fuel economy ratio (FE in km/l) in the range of 0.75 to 0.80. This range is greater than the E100 / E22 energy content ratio which is approximately 0.70. The customers very well perceived the higher efficiency of the ethanol-fueled vehicle when the low E100 / E22 price ratio at the pump played a major factor for this perception. The Flex Fuel Vehicles (FFV) were introduced in Brazilian market in 2003 with a single engine hardware and proper controls software and calibration to adjust engine operation according to the fuel being used. Since then, E100 / E22 FE ratio has practically matched its fuels energy content ratio. There are some ongoing initiatives to enhance E100 fuel conversion efficiency in FFVs in order to increase ethanol usage and the benefits of this renewable fuel for the society: lower fossil CO2 and less economic dependence on oil. In Brazilian recent fuel efficiency legislation - INOVAR-Auto - there is an amendment that specifies tax deduction incentives for OEMs with vehicles that meet the criteria of E100 / E22 FE ratio greater than 0.75 , without degrading E22 fuel economy. There are some researches sponsored by FAPESP and conducted by four universities at São Paulo  state aiming at developing engine technologies to increase E100 fuel conversion efficiency. This paper presents an analysis of the current status of 2017 FFVs FE ratio according to the official type approval data published in CONPET site. The effects of more advanced engine technology like direct injection, variable cam-phaser and turbocharging are also included in the analysis. A thermodynamic study is presented in order to correlate the main differences in physical properties of both fuels, like octane range and heat of vaporization, with engine typical BSFC maps and operation region in FTP tests. As a result, expected limit values for the E100 / E22 FE ratio of FFVs are provided according to engine technology. This paper also discusses the relationship between FE ratio and vehicle fuel efficiency.