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Just the right sizeEnter the watercraft engine. This model's focus was to meet the environmental challenges facing the watercraft market, but when Polaris withdrew from that market due to steadily declining demand, this promising engine became a viable alternative for its snowmobiles.
This engine has all the right parts to shine as a high-performance motor. With a short 66mm stroke and 85mm bore, it's built to handle much higher engine speeds and consequently has more power than the ATV unit. Four valves per cylinder, two intakes and two exhausts ensure good breathing at higher engine speeds. There are no pushrods here, and the valves are activated by an overhead camshaft. They also have a narrow included angle, necessary for an efficient combustion chamber design.
The only thing in common with the ATV is the 360-degree firing interval. This means both pistons rise at the same time, but fire on alternate strokes. This configuration may be a little harder to balance than a 180-540-degree crank, but the balance function is taken care of by a separate balance shaft.
When asked about their choice of firing order, the Polaris engineers were strongly in favor of the 360-degree layout because of its smoother firing sequence and better tuning of intake and exhaust pulses. This firing order is also easier on the belt drive and internal components like pumps and valve trains. The oiling system is by dry sump, which means there's no drag on the crank during cold winter mornings. That should make this one easier to start in the cold. Like all new 4-stroke sleds, starting is exclusively electric, too.
The engine is liquid-cooled, but there's also a good-sized oil cooler. A Bosch engine management system takes care of both ignition and fuel injection functions. This Bosch multi-port fuel injection system is just like what's used in today's cars, and includes rpm, throttle position and intake pressure inputs, as well as air temperature, water temperature, oil temperature, barometric pressure, and finally acceleration and deceleration maps for maximum fuel economy and emission performance.