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Ten years ago people shook their heads if you wondered whether a 4-stroke snowmobile would be competitive against 2-stroke technology.
Early attempts by OEMs such as Ski-Doo proved skeptics right, as heavy and slow were the most common adjectives used to describe the first 4-strokes. But, Ski-Doo engineers noticed 4-strokes worked well in two-up touring sleds, which led to the first V-Twin 1000, based on a motorcycle model.
Attempt No. 2 was based on the V-Twin 800 ATV engine and was light, but at 70 hp, not a real performance machine. Like everyone in the industry, Ski-Doo was dialing in on the bull's-eye, and it took until this new 1200cc 4-TEC triple was released for '09 to hit the red circle dead center.
4-TEC steps forwardThis is the first purpose-built 4-stroke snowmobile engine from Ski-Doo's Austrian engine maker, Rotax. With 130 horses at 7,750 rpm, a wide torque band and a total sled dry weight of 499 lbs. in the new XR chassis, Ski-Doo is sitting right in the center of the largest snowmobile sales market segment with a competitive sled.
So what happened to Ski-Doo's claim to stick with 2-strokes forever?
Ski-Doo is still committed to 2-stroke development. Its new clean-burning E-TEC engine proves that. But if you want to remain No. 1 in sales, you can't ignore the growing number of 4-strokes being sold. A market leader will have to offer a mix of 2- and 4-stroke machines to stay on top.
There are nearly 1.5 million snowmobiles in use in North America. Presently, only 5% are 4-strokes, but if the 4-stroke market share grows to 50% in the next 10 years, it will mean that something like 700,000 4-stroke sleds should be made in that period. It doesn't take a genius to figure out the opportunity in that slice of the pie.
Rotax is no newcomer to 4-stroke technology; it has a long history in making world-class motorcycle engines for European customers like BMW and Cagiva, and BRP's Sea-Doo watercraft brand, which has a supercharged 4-stroke engine.
What we're seeing in the new 4-TEC engine could just be the tip of a substantial performance-line addition. Down the road, we could see a 175+ horsepower "king of the hill" performance sled. Ski-Doo insiders say we'll probably not see a blower on the snowmobile, because on- and off-trail loading is more abrupt than watercraft applications and makes it hard to design a reliable drive for the blower. More likely is a higher revving engine in a performance application.
Strong designThe crank in this motor is a strong automotive style plain bearing design with a short 60mm stroke. By comparison, Yamaha's Nytro has a 66mm stroke, while the stroke on the high-revving Apex 4-cylinder is shorter at 58mm. Now, the piston diameter on the Rotax is 91mm, which gives the 3-cylinder engine an 1170cc displacement.
A 4-valve head with double-overhead camshaft and a narrow included valve angle is state of the art, and nowhere near breathing capacity with only 130 hp at 7,750 rpm. This engine could easily live and breath at 9,500 rpm, which would mean a potential 175 hp, even without a turbo or supercharger. Could such an engine power a new Mach?
The overhead camshafts are chain driven to the intake cam, and a set of gears from the intake cam then drives the exhaust cam. Instead of using traditional buckets for the cams to run against, the engine uses finger followers similar to a top-line BMW auto engine. Finger follower designs mean less mass in the valve train and reduced engine noise.
Valve clearance is adjusted by conventional shims, but with this design you can replace shims without removing the cams and having to re-time them. Removing a plastic insert on the finger follower shaft allows you to slide the follower sideways to change the shim stack.
How often do you have to do this? Ski-Doo says every 12,500 miles, which in most cases means something like every 5 years. So it's not a high-priority maintenance item. Regular oil changes with new filters are recommended at 1,865 miles, or once per season.
The oiling system is a dry sump design, which means two gear driven pumps at the bottom of the crankcase suck the oil out of the pan and deliver it to the oil tank through an oil/water cooler. One pump draws oil from the pan, while a smaller pump draws oil from a cavity formed between the last plain bearing on the crankshaft and the outside ball bearing support on the clutch side.
The cavity gathers oil from the head, but is curiously large enough to perhaps house a reduction gear if needed for a higher revving engine. A separate gear-driven pressure pump supplies oil to the crank and camshaft bearings and also sprays the pistons' undersides for extra cooling, as in a Formula 1 racecar engine.
The oil cooler sits in front of the engine by the water pump, while the oil tank is mounted directly to the engine block under the intake plenum. The dry sump design means that the engine can be mounted extremely low in the chassis for a better center of gravity. This is important because chassis roll due to the heads' extra mass is a drawback in 4-stroke designs.
To ensure a smooth running engine, a gear-driven balance shaft is installed in the engine's front, and it also drives the water pump. Air is fed into a large plenum through a single 52mm throttle body, but the fuel injectors are mounted at the end of a long set of runners close to the inlet valves for even fuel distribution to each cylinder.
The large plenum box dampens the inlet flow, and the long runners ensure strong torque at low rpm. This contrasts with the Yamaha design that has separate throttle bodies closer to the valves. The result is a marked difference in throttle response. While the Yamaha has a strong and quick response, the Ski-Doo has a smooth and progressive response, tailored more to the touring market.
An electric starter engages a ring gear on the flywheel through a reduction gear mechanism. The flywheel is equipped with rare earth magnets, which give a stronger electrical output at lower rpm. Sparkplugs are fired by coils mounted directly on top of them, automotive style. The ignition is a digital induction design as used in cars, and produces a strong spark like in a CDI, but with a longer duration to fire richer mixtures on cold days.
Extra attention was directed to the exhaust in a significant effort to reduce sound levels. BRP worked with Austrian consultants to develop an exhaust note communicating refined performance. European sports cars were used as the benchmark.
Electronic engine reverse can only be used on 2-strokes, so its use on the 4-TEC application was not possible. Instead, Ski-Doo developed a new reverse design in the top of the chaincase off the secondary shaft. This is a lighter and simpler design that weighs half of the earlier design. With 8 parts instead of 27, it saves 3.9 lbs. and gives more legroom. Reverse is electrically activated via a push button that engages a stepper motor.
First impression?
The 4-TEC feels very refined. The engine hums along without vibration and the low-end engagement comes in softly. Acceleration is smooth and consistent with good midrange torque. Throttle response is not a snappy "rip your arms off" feel as with Yamaha's Nytro, but rather a turbine-like steady pull that is somewhat deceiving and gets you up to speed a lot quicker than you think if you don't keep an eye on the speedo.
In handling, there's no heavy 4-stroke feel that can make these sleds roll more in the corners due to a higher center of gravity. Several times I had to look at the hood for the 4-TEC XR label to make sure I was on a 4-stroke. I also liked the ride calibration on the XR chassis. Since the power comes on smoothly, there is no excessive transfer in the rear suspension. I also felt that the front ski suspension worked somewhat better here because of the few extra pounds up front to work against the springs.
Lighter machines like the XP are more sensitive to shock and spring calibration and often are set up a little too stiff and aggressive for me, although the young "mogul buster" crew seems to love that set-up. We are not all "mogul busters," although it may be fun for a bit. About 95% of the time I prefer a sled that is set up a little softer for a smoother, but still responsive, ride on a groomed trail.
The 1200 4-TEC is well calibrated for that "sports car" feeling. BRP has hit the center of the market with a product that does everything well.
By the way, did we mention the best emission rating, plus 18 mpg fuel mileage and a tank large enough to give you a range of 150+ miles? All very nice, but I'd get it just for the refined ride and smooth power.