4strokes breakin out

AmSnow.com is now SnoWest.com

With Ski-Doo now offering a 4-stroke engine, all of the manufacturers are hedging their bets in the emissions game.

While Yamaha is fully committed to a 4-stroke only lineup, the other three majors offer both 2- and 4-stroke machines. By offering some 4-strokes, they gain points that can be offset against less efficient fan-cooled models in the EPA forced "fleet average" game where sledmakers work to keep the average emissions of their fleet within EPA guidelines.

With Arctic offering its new 1056cc 123-horsepower 4-stroke Jaguar, and Polaris with its 140-hp turbocharged 750cc FST, the two American players are aiming to sell to the market's fat center, while still keeping some fan-cooled models. Ski-Doo on the other hand is positioning itself to possibly replace the fan-cooled entries with its new 65-hp 800cc V-Twin It also may use the extra emission points from the 4-strokes to enable it to keep the popular larger 2-strokes in its lineup.

Ski-Doo 4-TEC
The Ski-Doo 4-TEC V-800 EFI twin was a fun surprise when I tried it at the preview in Upper Michigan late last season. At first look you might think this would be an underpowered 4-stroke, and disappointing experiences with the early Polaris Frontier ATV-based 800 twin come to mind. Memories of Ski-Doo's first try, the sluggish big V-Twin 1000, made me skeptical.

But talking to AmSnow's founding editor Jerry Bassett at the preview, I found him enthusiastic about this Ski-Doo entry. After I rode it I knew why!

For starters, Ski-Doo claims the 800cc ATV-based engine to be 40 lbs. lighter than the old 1000 V-Twin. This lighter engine is installed in the sprightly Legend chassis along with electric start and mechanical reverse, all at a claimed dry weight of 490 lbs. for the Trail model and 510 lbs. for the Touring version.

The engine has a light, quicker-revving feel than the old V-Twin, and on the wide, open U.P. trails, I easily hit 70 mph. At that speed the rear suspension outperformed the single A-arm front suspension, but knowing how these demonstration models get trashed, the shocks were probably worn. The wide power band and EFI makes this an easy engine to live with.

The engine is the same as the top-of-the-line Can Am Outlander ATV, presently the most powerful ATV you can buy. Ski-Doo claims 65 hp at 7,000 rpm, which puts the V-800 in the 440 fan class, but this is a mild state of tune. ATV's require emphasis on bottom-end torque to slug through mud, while snowmobiles can live well with less bottom-end torque, needing more mid- and top-end power.

With the short 61.5 mm stroke, the engine could easily be revved to 9,000 rpm or higher with a few camshaft changes. This would put 80 to 90 hp within reach, and position it with the top-level fans. Throw in a REV double A-arm front suspension to handle the extra performance and you would have an extremely fun machine.

Ski-Doo chose an 80-degree angle between the cylinders, claiming this configuration results in the best balance and lowest vibration levels without adding balance shafts. A single chain-driven overhead camshaft activates 4 valves in each cylinder, offering plenty of breathing potential for higher power levels.

Another clever feature is the dry/wet sump system. The oil is drained from the bottom of the crankcase into a second oil sump that also acts as a built-in oil tank. The system has the advantage of a low friction dry sump system, but eliminates the need for a separate oil tank with all the plumbing and added bulk. This in turn makes the installation easier and keeps the oil low in the pan for a lower center of gravity. With the short stroke V-Twin configuration and only a single overhead cam per cylinder, the sled does not have that top-heavy feel of some 4-strokes.

Arctic Cat Jaguar Z1
Arctic Cat's new 1056cc Jaguar engine aims at a vastly different market segment than the Ski-Doo. We're talking about an engine aimed at the 120-horse crowd - the majority of sled buyers. Arctic pulled out all the stops to make sure the engine has the bells and whistles to make it successful.

In the power department, there are 4 valves per cylinder, activated by chain-driven double overhead cam and bucket followers. Each cylinder breathes through huge 48 mm fuel injector bodies, and the exhaust system is fabricated from stainless steel for reliability at the higher heat loads. Both pistons rise and fall in parallel, giving a 360-degree firing order, meaning one power stroke per revolution. This is the same configuration Polaris chose for its 750, because an even firing order makes it easier to run a turbo.

Could this be the next sled for the aftermarket turbo crowd?

The crankshaft webs are heavily pork chopped for low weight to produce a quick revving motor and give the power band a 2-stroke feel. To make sure any vibration is under control, Arctic installed two balance shafts, one on each side of the engine. This adds weight, but is a huge insurance against harshness and vibration. There also are motor mounts high on the block, close to the center of gravity, that alleviate concerns about vibration reaching the frame.

The engine is laid back to center the mass, and a shallow dry sump pan makes it possible to drop the engine way down for a low center of gravity. Oil is cooled by the engine water coolant before it is returned to the tank. The oil system includes a low-pressure engine shut down, and the oil tank has a spill-proof "tip-over" design.

Arctic also has addressed a potential heavy engine-braking problem with a new-patented anti-engine braking system that produces a coasting feel when releasing the throttle. It's similar to a 2-stroke sled so the learning curve for former 2-stroke riders is small.

The EFI system features a pressure sensor that adjusts both fuel delivery and spark advance according to elevation changes. An additional oxygen sensor in the exhaust system makes the EFI a full loop feedback system combining good fuel economy with maximum performance.

It's obvious that Arctic and Suzuki engineers have thought long and hard about their new purpose designed 4-stroke, and it has plenty of potential as stricter emissions take hold.

New engine data
Ski-Doo 4-TEC V-800
Displacement: 800cc
Bore and stroke: 91 x 61.5
Cylinder configuration: 80-degree V-twin
Hp/rpm: 65 at 7,000
Fuel system: EFI - single 46 mm
Oil system: Dry/wet sump
Ignition system: 3D inductive CDI
Cooling system: Liquid

Arctic Cat Jaguar Z1
Displacement: 1056cc
Bore and stroke: 98 x 70
Cylinder configuration: 360-degree parallel-twin
Hp/rpm: 123 at 8,600
Fuel system: EFI - twin 48 mm
Oil system: Dry sump - oil tank
Ignition system: Transistor coil at plug
Cooling system: Liquid

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.