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800 overhaul
Polaris did not stop with a new chassis, the 800 H.O. engine got a large overhaul with some exciting new features. The power valves are now computer controlled via a stepper motor, which allows the use of a 3-step design. The power valve now consists of two slides that interact with each other. In the fully closed position, both the side port and the main port are closed. The side ports are then uncovered so only the main port is blocked. Halfway up the travel, the side port slide grabs the main slide and both travel out of the way to leave the port fully open. The mechanism is no longer a simple single slide, so in order to make sure it works correctly, Polaris has added an extra cooling circuit to keep the parts at a consistent lower operating temperature.
New on the 800 H.O. engine is also an electrical computer-controlled oil pump. The electronic oil pump eliminates the power robbing gear drive and provides an improved, more precise oil delivery. A number of oil lines are routed to supply the crank bearings and also squirt oil directly onto the big end rod bearings. This is necessary because no oil is carried into the crankcase by fuel due to the use of Polaris’ version of a semi-direct injection system. One injector is mounted in each cylinder feeding into the back transfer port, but no fuel is transferred into the crankcase through a slot in the piston as with the new Arctic design.
Since there is no fuel cooling of the crankcases, the engine has very generous water cooling passages from the water pump on the front of the crankcase. Intake flow is controlled by throttle bodies breathing through case mounted reed valves. With no fuel going through the crankcases, the main transfers inject clean air, so there is less chance for fuel mix to escape thru the exhaust port, and this then reduces unburned hydrocarbon emission. Polaris feels that they can meet existing emission standards with this system, which has the benefit of being less expensive and simpler than a high pressure direct-injection system into the combustion chamber like Ski-Doo’s E-TEC. If it becomes necessary to have a direct-injection system, Polaris has a high pressure direct-injection system based on the new automotive systems now in use, but it is more expensive and more complicated.
At the present time EPA has backed off and decided to keep the present emission standard for the foreseeable future. We think this is due mostly to the large improvements in emissions and positive attitude shown by all the snowmobile manufactures. This is a great result for all who worked on the popular 2-stroke engine with all its inherent advantages in both power and weight.
The new Polaris 800 engine has been in constant development since 2008 and early teething problems are now way back in the rearview mirror. Power has steadily improved and is now on the level with its rivals. Power delivery is greatly improved. The wide and torquey power band and the always efficient Polaris clutches combine to deliver strong class-leading acceleration. There is also a new crank that’s 2.5 lbs. lighter with 25 percent less inertia to make corner to corner spurts even quicker.
Polaris has made a large effort to make sure the new AXYS 800 is a top model in the very competitive 800 class. The new 60th anniversary RUSH and Switchback models now have all the right parts to make them strong contenders with class-leading engine performance.