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2017 Ski-Doo Tech Update

An inside look at the new 850cc engine and Gen4 REV chassis
2017 Ski-Doo new motor engine
2017 Ski-Doo new motor engine
Shorter, more compact throttle bodies with injectors improve both acceleration and top end power. The electric starter motor now works directly on a ring gear mounted on the magneto flywheel, and should add a new level of durability as well.
Innovations from Ski-Doo have advanced the state of snowmobile technology each year for nearly a decade. Some, like the REV chassis and E-TEC engines, have been big leaps, while other innovations have been features like new suspensions, tracks, roller clutches and skis. For 2017, Ski-Doo aims to protect its No. 1 market status with a new chassis and a new engine. Both are progressions of already proven products, but with new features for added performance and durability.

The science behind Ski-Doo 2017
The new Doo chassis has been narrowed in front in order to position the center of mass of the engine on the center line of the chassis, essentially moving the engine some 2.5 inches to the right. As tracks get more aggressive with more hookup, and engines deliver more torque and horsepower (160+), mass distribution becomes even more important for handling. When the center of mass is offset, the snowmobile will turn in the direction of the offset, because the inertia of the engine’s mass creates a torque reaction when accelerating hard. Keeping the mass centralized in the lateral direction improves both directional stability and ease of maneuverability, so Ski-Doo is developing serious traction hookups and hard acceleration with its new engine.

A number of the new engine's features can be found in both automotive and diesel engines. The new crankshaft has only two pieces that are press-fit together in the center. This means the crank pins are solid and cannot twist, which is more like an automotive crank pin design. To accomplish this, you need a split rod with split roller cages. This comes directly from the outboard engine, where this is a very established practice going back to before WWII. This is not a first in the industry; Evinrude and Johnson snowmobiles all had one-piece cranks, and both split rod and center bearings, as do most current 2-stroke outboards. Fracture-split rods and center bearings can only go back together the way they were originally split, and this gives them an interlocking matrix surface that is very strong and accurate in locating bearing surfaces.
2017 Ski-Doo new two-piece crank split-bearing design
The new two-piece crank utilizes rods with a split-bearing design.
2017 Ski-Doo new two-piece crank split-bearing design
So why did Ski-Doo not go all the way and make a one-piece crank with a split center bearing? My guess is they like the center worm gear drive that runs the water pump. Locating the water pump on the outside by the starter housing would probably have made the engine three inches wider and two pounds heavier. The piston is forged, but it has a steel insert as a ring carrier. This diesel technology ups durability by providing a much harder surface for the rings to “hammer” against, something that usually wears out aluminum ring grooves faster.

The bore surface in the cylinder is also now coated with plasma-sprayed iron powder.  The advantage is a steel running surface that is more porous than Nickel-Silica coating to hold a better oil film, but with much better heat transfer than a thicker steel sleeve. This is also well-proven technology, but more expensive than Nikasil coating. There is also room for expansion with this design. With an 82mm bore and a longer 80mm stroke, just a small increase in bore by 2.5mm will up the displacement to 900cc.

The E-TEC injection system is now in its second generation with a major redesign. The injector housings are now one pound lighter than the 800 E-TEC and managed with greater precision. The new engine management electronic is twice as fast as the E-TEC 800 (32 million cycles per second). In addition, Rotax added one regular injector in each throttle body to improve acceleration. Think of them acting as accelerator pumps in a carb.

AmSnow associate editor Ross Halvorson, who had a chance to try the new sled at the introduction in Quebec, reported amazing response at any speed and throttle position, which combined with the new primary roller clutch made it not only very quick, but also very smooth. You can read the rest of his early ride impressions here.

Additional features are three-way power valves (which react three times faster than the 800 E-TEC), a smaller three-chamber muffler and a better flowing and quieter air box with separate tuning chambers that match dominant frequencies.

Even with these gains in power, torque and response, fuel consumption remains at 19 mpg, while oil consumption has been reduced by 40%.
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