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When I saw Ski-Doo's new 800R PowerTEK Engine last March, I was disappointed that it will only be available in Summit models this year. Looks like I'll have to wait until next season to run this refined motor on Wisconsin trails.
It's no secret that the 800 H.O. REV models are a favorite of hard-charging enthusiasts. With the REV's legendary handling and power delivery, it's the king of the twisties. So why is the 800R only available in a mountain sled?
Mountain climbing puts the highest stress on an engine, so it'll be well tested before it hits the mainstream Midwest flatlander markets. Moun-tain riders also have cried for more power in a lighter sled, and this is Ski-Doo's answer to those who feel 900s and 1000s are too weighty.
New - crank to castingsNo single item magically boosted the 800R's power, rather it was a number of refinements. Although the design is based on the proven 800 H.O. model, this engine is new from the crank to the castings.
Start with the crankcase, which is extensively redesigned with a beefed up crank supported in larger bearings. A clever design creates a pocket for cooling water between the power frame and the bottom of the crankcase, wrapping water around most of the bottom half. Cooling flow is increased 30% by using the same pump as the 1000 Mach Z engine.
Keeping the crankcase cooler increases power by delivering a denser charge to the cylinder and also makes the engine ready for a future switch to SDI, if that's needed to meet future emission standards. More power also is harvested from the cylinders, which are now a mono block design with two cylinders in one casting. This makes room for larger intake and transfer passages, plus a 5% larger exhaust port. The mono block also stiffens the entire engine assembly and provides more room for better cooling flow. A stiffer engine twists less, resulting in reduced friction losses, and less friction means more power at the output shaft and longer component life.
Added featuresSki-Doo engineers weren't content with just redesigning components, they added important features to both the carburetors and power valve system, making this possibly the most advanced 2-stroke snowmobile engine to date.
Ski-Doo chose to keep carburetors for the ease of tuning by the customer, but then added features to make it possible to computer control the mixture as with electronic fuel injection. They wanted those who fine-tune their sleds to be able to change jets, yet they wanted to electronically adjust the mixture according to conditions such as temperature and altitude.
The resulting system is a clever mix of both carb and EFI. Fuel flow through the carburetor jets is controlled by creating a vacuum in the float bowls. This vacuum is controlled by a high-frequency solenoid valve that changes the amount of vacuum in the float bowl based on a map in the ECM (Electronic Control Module). This not only compensates for temperature and barometric pressure, but if your octane rating varies, the knock sensor will pick it up.
The signal from the knock sensor not only retards the ignition as on earlier models, but also richens the fuel mixture. Richening the fuel mix in response to pre-ignition knock is better than just retarding the ignition, as a richer fuel mix cools the piston quickly, more effectively preventing damage. Until now this had been exclusive to fuel-injection systems, but with the introduction of the ECM controlled float bowl vacuum, owners can tune the baseline with jets and still have the advantage of electronic mixture compensation based on conditions.
New power valveSki-Doo pioneered the RAVE power valve 25 years ago and it has remained in its basic form ever since. Power valves not only produce better bottom-end torque and improved mid-rangepower, but also prove to be an advantage to both sound reduction and emission control at lower engine speeds.
The new system is called 3D RAVE because it has three opening positions, controls three exhaust ports per cylinder and 3D computer mapping determines its operation.
Here's how it works: each power valve assembly consists of two guillotine plates sandwiched together. One plate controls the main exhaust port, and the other controls the side exhaust ports. A 42% larger diaphragm bellows is then operated by crankcase pressure or vacuum, and an ECM signal operates two solenoids, which applies either pressure or vacuum to the diaphragm.
For ease of starting, the side ports are kept open, but as soon as vacuum builds up at around 800 rpm, the side ports are closed, together with the main port, and stay closed to 6,200 rpm. Between 6,200 and 7,400 rpm the vacuum is switched off and the side ports open again for more exhaust flow.
Above 7,400 rpm the other solenoid switches to pressure and both valves move out of the way for full open exhaust flow on top end. The vacuum and pressure signals are generated from one-way valves in each crankcase housing and fed to the solenoids.
The double guillotine system is more complex than earlier models, and you wonder what kind of sticking problems the mechanism might have. Ski-Doo engineers assure me that this has been addressed with not only two special coatings on the slides, but also by drastic changes in water passages around the housing to keep it cool.
In addition, hot exhaust gases are not used to move the mechanism any more, but rather cold gases are used from the crankcase. Ski-Doo is so confident in this system that they do not even require synthetic oil for protection.
The air box also is changed to use a larger diameter inlet tube for better flow. This is needed because the engine now revs 500 rpm higher.
A larger exhaust manifold and a new single pipe are tuned with the new porting to produce power at 8,250 rpm, and the muffler is a lighter three-chamber design. With power increases coming from less friction, a cooler intake charge, improved porting, higher engine speeds and a new exhaust, 151 horsepower is being delivered to the output shaft.
With these new features the 800R PowerTEK should be positioned well for future challenges both in the emissions and power departments.
Olav Aaen is a long-time contributor to AmSnow. As a mechanical engineer and president of Aaen Performance, Olav has been heavily involved with snowmobile performance since 1968. Aaen Performance is best known for pioneering performance pipes and introducing the roller clutch to the snowmobile market.