The University of Idaho's (UI's) entry into the 2009 SAE Clean Snowmobile Challenge (CSC) was a semi-direct-injection (SDI) two-stroke powered REV-XP snowmobile modified to use flex-fuel. The flex-fuel engine produces stock engine power on any blend of ethanol and gasoline from E10 to E85. The emissions output was reduced using an oxidation catalyst located after the exhaust silencer. Noise from the engine compartment was reduced by custom-carbon fiber hood and side panels, which allowed placement of extra sound absorbing materials. The UICSC design produces 80.5 kW, is lightweight at 238 kg wet, and achieves a fuel economy of 5.65 km/L on E85 fuel. The UI snowmobile achieved Third Place in the competition, while producing the best fuel economy and winning several other awards, including Best Acceleration, Best Value, Best Ride (fueled class) and Best Subjective Handling.Ethanol content feedback was accomplished using a flex-fuel sensor that continuously measures the ethanol content of the fuel. A custom circuit was built to relay the information from the flex-fuel sensor to the engine control unit (ECU) and display the ethanol content to the rider using an LED display.The University of Idaho has developed a cost-effective semi-direct-injected two-stroke snowmobile engine capable of running on ethanol/gasoline flex-fuel. The SDI two-stroke snowmobile maintains the mechanical simplicity and low weight avid riders enjoy, without sacrificing the clean and quiet characteristics necessary to meet current and upcoming standards.