Clean snowmobile technology has been developed and applied to a commercially available two cylinder, four-stroke snowmobile. The goals of this effort included reducing exhaust and noise emissions to levels below the U.S National Parks Service (NPS) Best Available Technology (BAT) standard while increasing vehicle dynamic performance with a 50 percent peak power increase over the original equipment version.Engine thermal efficiency has been increased through Late Intake Valve Closure (LIVC) valve timing modification for Miller cycle operation, while high load power was increased through the implementation of a turbocharger and variable electronic boost control. An electronic throttle was also implemented in combination with a “performance/economy” mode switch to limit speed and increase fuel efficiency per the rider's demands. Additionally, a new exhaust system featuring a three-way catalytic converter and a simple, lightweight muffler utilizing a passive acoustic valve has been developed to reduce chemical and noise emissions. This snowmobile was modified to run the full range of ethanol-blended fuels using an affordable flex-fuel sensor and custom controls, including closed-loop wideband exhaust oxygen feedback. Excellent fuel efficiency was achieved with the lean-burn Miller cycle powertrain in addition to an exhaust emissions improvement of 13 percent from the original equipment version.