Just how polluting are snowmobiles? During a peak winter visitation day in Yellowstone National Park, snowmobilers using the standard two-stroke engine sled would release as much as 20 tons of hydrocarbons and 54 tons of carbon monoxide into the air. For comparison, an average peak visitation day in July would see cars emit only 2.5 tons of hydrocarbons, and 17.5 tons of C02. It’s no wonder that two-stroke snowmobiles have been banned from the Park since 2003.
Answering the call, the cleaner, quieter 4-stroke snowmobile has been mass distributed since that time. The 4-stroke engine holds a laundry list of operational improvements and fuel efficiencies compared to the 2-stroke:
• A 2-stroke engine allows a charge of raw fuel (20 to 33 percent), a mix of oil and gas, to escape through the exhaust pipe; in the 4-stroke engine, the oil remains separate from the gas. This also means a 4-stroke will require only periodic oil changes, unlike the 2-stroke’s constant need for oil.
• 4-stroke engines use electronic fuel injection instead of carburetion, making the 4-stroke sled up to 65 percent more fuel efficient.
• A 4-stroke sled reduces hydrocarbon emissions by at least 90 percent and carbon monoxide emissions by at least 70 percent.
• The 4-stroke’s gas and oil costs are typically 35 percent less than a 2-stroke’s.
A few years ago Aspen Skiing Company made a huge move to four-stroke snowmobiles. Currently, 45 percent of the company’s sled fleet are 4-stroke snowmobiles, and the CO2 reductions have been significant. The company has saved approximately 40 percent in gas costs since switching to 4-stroke sleds, with comparable CO2 emissions reductions as a result of the higher efficiency.
But because the 4-stroke engine is still relatively new, and is subject to more wear and tear as a utility vehicle for ski resorts compared to recreational use, Aspen saw maintenance costs soar with its 4-stroke sleds.
Problem solved: snowmobile manufacturers have introduced refined, even- more-efficient direct injection (DI) 2-stroke engine sleds. Polaris, one of the leading DI 2-stroke manufacturers, uses what it calls cleanfire injection. Two-stroke engines are much lighter than 4-strokes of the same power as well as much simpler, usually meaning less maintenance. The DI 2-stroke engine further reduces the weight of the standard 2-stroke design, while at the same time eliminating the pollution produced by a carbureted 2-stroke and increasing its efficiency. A 150-hp direct injection 2-stroke weighs 70 pounds less than a 150 hp 4-stroke (a difference of about 15 percent). Polaris’s cleanfire 2-stroke engine produces almost the same level of emissions reductions as the 4-stroke, but gets 19 mpg, which is slightly better than most 4-stroke sleds.
Aspen continues to operate 4-stroke snowmobiles at many of its resorts, but all new sleds purchased are DI 2-strokes. Among the current DI 2-strokes sleds in the fleet are the Polaris RMK 600 155 es, Polaris Turbo Switch Back and the Ski-Doo SM Expedition TUV 600SDI.