AmSnow.com is now SnoWest.com
Emission regulations have been driving snowmobile design for the last 5 years, and probably will for years to come.
The future of snowmobiling hangs on success in several areas, not only on the technical side, but also on the marketing and political side. Some manufacturers, such as Yamaha, have left 2-stroke engines and are betting on an all 4-stroke future. Others, like Ski-Doo, are confident that they can meet future demands with cleaner high-tech 2-strokes.
The two American manufacturers have settled in-between, working on both 2- and 4-stroke models. In a shrinking market, hit both by shorter winters and lack of consistent snow cover, the manufacturers are faced with an unprecedented investment in retooling for new engines. Bad timing!
Yamaha, who had the smallest market share, has possibly invested the most in a stream of new 4-stroke models. As a result, its sales have shown a healthy increase, and it now holds the lead in 4-stroke designs, with sophisticated engines based on its motorcycle expertise.
Ski-Doo is No. 1 in sales right now though, and has been making steady advances in 2-stroke emission technology. Not only has Ski-Doo's constant development of the SDI (Semi Direct Injection) electronic fuel injection paid dividends, but with its purchase of the OMC (Evinrude-Johnson) Outboard Group, the company also has advanced direct cylinder injection technology available and already in the market.
The Evinrude and Johnson outboard brands now boast of light 2-stroke engines that beat the 4-strokes in both emissions and fuel economy. It's no great secret that Ski-Doo snowmobiles are already being tested with direct-injection outboard systems. With all this injection technology available, it's perhaps curious that Ski-Doo is still developing electronic carburetors to meet emission requirements.
Yet there are good reasons for continuing with carb development. First, snowmobilers are used to tuning carbs, and changing a couple of jets is a lot simpler than getting involved with computers, if you can even get access to the programs. Carburetors also can be tuned over a wider range.
The problem with fuel injection is the cost of electronics and the limitations of the injectors themselves. If you pick a single injector per cylinder to deliver enough fuel for top-end power, the same injector may not be tuned to be lean enough at idle and low speed. As a result, two injectors usually are required; a smaller one for low speeds, and a second to increase fuel delivery at full power.
Both Ski-Doo and Polaris have a smaller low-speed injector in the transfer passage that is timed to inject fuel after a large dose of fresh air has entered the cylinder. Arctic showed us a similar system last March, but dropped it from production and went back to its proven throttle body injection system, claiming it could meet emissions with the simpler system by using advanced features like its exhaust gas temperature sensor in the pipe.
Complications add cost, and multi-injector systems need advanced electronics, more pickups and timing systems and an ever-growing wiring harness. In addition, if you want to tune the systems, you (at least) have to invest a couple of hundred bucks in an EFI tuner box.
Biggest advantageThe biggest advantage of electronic injection is that it can adjust itself to temperature and altitudes. Ski-Doo has this adjustability in its PowerTEK system by controlling the pressure in the float bowl via an electronic solenoid. The solenoid is steered by an electronic computer box with the same sensor inputs as the fuel injection system.
A carb is a mass flow sensor, it flows fuel in proportion to the mass of air entering the engine. A good carb has at least three tuning circuits, a pilot and low-speed circuit, a mid-range circuit consisting of a needle and needle jet and a top-end circuit controlled by a main jet and calibrated air-passages. As a result, Ski-Doo claims that it can now calibrate the low-speed fuel flow accurately enough to meet emission rules.
Emission control in 2-stroke engines is all about preventing un-burned fuel from entering the exhaust system. At higher engine speeds when the plugging pulse from the tuned exhaust pushes the fuel back into the cylinder again, the problem is simpler. It is at the lower engine speeds when the exhaust is "out of tune" that fuel must be stopped from escaping out the exhaust port.
We are seeing some new approaches from Ski-Doo in this area. In its 550 fan-cooled engines, engineers have reduced the width of the exhaust port by 6 mm and lowered it 2 mm in North American models, compared to the engines used in Scandinavia. A hint at future directions may be Doo's new 800R, where two power valves control either the side exhaust or the main exhaust.
There probably will be a change in cylinder port layouts in the future, where the main side transfers will be directed more away from the exhaust ports and possibly made smaller while the main exhaust port becomes narrower to prevent fresh air from escaping at low speed.
Exhaust manifold design also influences emissions. Presently, some twin manifolds allow the pulse from one cylinder to create a plugging action in the other at low speed. The side effect may be top-end power loss on some sleds, which makes the aftermarket guys happy to sell performance manifolds.
Don't be surprised to see high-tech manifolds with electronically controlled gates and passages to control emission at low speed, as this technology already exists in 4-stroke exhausts. A triple engine with a three-into-one exhaust may also come back, because the three-into-one manifold offers a good plugging action at lower engine speeds that could offer emission advantages.
Snowmobilers love the lightweight and responsive power of 2-stroke engines, as well as their simple design. Manufacturers, who can meet future emission standards with a light, powerful 2-stroke, may have an edge in the marketplace.
To that end, Ski-Doo, Arctic and Polaris are all using their engineering resources to make sure they meet the emission challenges. This time the stakes are high, if you fail to develop a clean 2-stroke engine while others succeed, you may lose a large chunk of market share.
Olav Aaen is a long-time contributor to the snowmobile industry. 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.