four stroke development explosion

Snowmobile four stroke development is exploding into a number of interesting directions. Originally the four stroke was a response to dubious complaints about noise and emissions by the Yellowstone Park staff. The original complaint was that employees in the Gatehouse at the entrance got sick breathing the fumes from the two stroke engines. Turns out that the Gatehouse could have been redesigned with better ventilation for the employees, but in today's politically charged atmosphere the manufactures decided to redesign the snowmobile instead. All in all, it was probably not a bad idea, as it has led us into some new and interesting directions. Whether the end result will be more four strokes, or if it will turn out to be more cost effective to clean up the two strokes remains to be seen. Whatever direction this new battle takes us, we intend to enjoy the ride and analyze all the new twists and turns.

Arctic Cat was first on the battlefront with its three-cylinder model. The engine was borrowed from a Suzuki mini car, and originally promised 45 hp. The machine was a direct response to Yellowstone demands. It was a clean and very quiet snowmobile, intended to be used as a rental unit for winter visitors to the park. 45 hp only gives you so much performance, and that is fine in the hands of first time snowmobilers wanting to take in the sights.

Experienced snowmobilers, used to twice the power, understandably failed to be excited. Arctic Cat has responded to these concerns by increasing performance by 8 hp on the '03 model.

Polaris took a quick and easy step into the four stroke market with a 780cc parallel twin borrowed from their hot selling Sportsman 700 ATV model. This kept the tooling cost down and allowed them to test the market place. The Polaris claims a 55 hp output, which places them comfortably in the first generation rental fleet market.
The industry may have been content to answer the environmentalist challenge with a line of politically correct low powered machines, but Ski-Doo got the idea to build a next generation four stroke that would satisfy the demand for more power.

Ski-Doo's entry into the performance market is a modern liquid cooled V-twin of 1000cc displacement and a rumored 90 hp output.

Rotax has considerable experience building four stroke engines for motorcycles, and the new V-twin design most likely borrowed from the experience gained with the V-twin engine they build for the Aprilia superbike.

Ski-Doo claims that this is a completely new design, and not an Aprilia engine mounted in a snowmobile chassis. This makes sense since the crankshaft design has to be considerably different to accommodate a snowmobile belt drive system. Bearings and crankcase supports have to be much stronger to take the bending loads from the belt drive, and it's doubtful that a motorcycle crankcase would have been strong enough to meet this challenge.

The Ski-Doo V-twin therefore represents a considerable investment in design and new tooling. The first version of the Ski-Doo snowmobile showed no great effort to redesign the chassis to take advantage of a four stroke design, but it is an early effort and a step up from the "politically correct" rental sleds. This snowmobile represents a strong second generation machine intended to address the mainstream sled market where power in the 80-100 hp range is expected.

We have no doubt that the same engineers who delivered the revolutionary REV chassis now are hard at work fitting the four stroke engine into a very special chassis.

Ski-Doo is also the first manufacturer to follow two parallel development paths, with the introduction of its new clean fuel injected two stroke models. Will the four stroke development stay up with the emergence of cleaner two strokes?

The crew at American Snowmobiler came to the conclusion several years ago, that four strokes eventually will have to stand on their own against cleaner two strokes, and this would require a very sophisticated four stroke machine that could match any of the two strokes in performance.

Yamaha answered that question with the introduction of the new RX-1 snowmobile. This is a true "third generation" four stroke, with an engine designed specifically for installation in a snowmobile, and a completely new chassis made to take advantage of the four stroke power. Yamaha developed a very sophisticated 5-valve technology for their Formula 1 race car engine and this is now found in both their road bikes and dirt bikes. This same high efficiency head design is used in the snowmobile, but the only things in common with the bike engine are redesigned versions of their high RPM crank, rod and piston components. These components are housed in an engine designed to fit in a snowmobile. The clutch is geared down from the 10,500 rpm to 8,500 rpm where the clutch runs most efficiently.

They effectively leap frogged the competition directly into a third generation design. It actually turns out that this is no coincidence. They have had an active four stroke program since 1979 and have already solved problems the other manufactures are now running into.

The first model tried in 1979 was a 400cc four stroke twin, but it was rejected for production due to lack of performance. Several additional prototypes were tried and rejected, the last as late as 1999. With 20 years of experience from building prototypes, Yamaha finally felt they knew how to build a good four stroke snowmobile, and the RX-1 is the result.

No doubt, four stroke developments have taken off in a number of interesting new directions aimed squarely at competing with two strokes on equal power terms. Will the two stroke lay down and disappear, or will we see cleaner two strokes with the obvious advantage of light weight and better power rebound and reclaim their turf? There are very interesting developments coming up in the two stoke world. Stay tuned for the next issue when we cover the two stroke battle for cleaner engines.