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Head to Head: 2- vs. 4-stroke

New technology shifting momentum back to 2-strokes

RELATED TOPICS: ENGINES
tech
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The Ski-Doo MXZ X-RS uses a high-tech Rotax 800R direct injected E-TEC 2-stroke.
“The news of my death has been greatly exaggerated,” Winston Churchill famously said, and the quote rings true today for the 2-stroke engine.

Every time someone predicts the demise of this lightweight and efficient power plant, it seems to pop back like a jack-in-the-box, stronger and faster than before.

There is no question that the 2-stroke engine is more powerful than a 4-stroke based on engine displacement and weight. To be competitive with a 600cc 2-stroke, a 4-stroke must displace about 1000cc and weigh up to 50% more. A lot of that extra weight sits high in the head, with all the camshafts and valves, and this affects a snowmobile’s handling.

Based on performance, the 2-stroke engine is ideally suited for snowmobile applications.
So why do all the manufacturers build heavier, more expensive 4-strokes today?

Politics and pollution
The reason comes down to politics, which reared its ugly head in the form of stricter emission requirements. Pollution from internal combustion engines is particularly a problem in the summer heat when there is a great concentration of vehicles in a small area.

A good example is Los Angeles in July, where 5 million cars pass through downtown during rush hour. The concentration of exhaust gases, combined with the high angle of the sun’s rays and temperatures above 70 F creates ozone that reduces visibility and forms air pollution.

Interestingly enough, it does not take much of a reduction in temperature below 70 F and the sun’s lower position on the horizon to greatly reduce ozone production. You’ll often hear people from Los Angeles say that during the winter months the visibility clears so much that they can actually see mountains in the distance, something they don’t see all summer.

What’s changed? The number of cars driving through downtown is still the same, just the temperature and the sun’s position have changed, and it’s not even cold enough there to snow!

Why sleds are different
With sleds the situation is different.

First, you will be hard pressed to find a truly large concentration of snowmobiles anywhere (we are talking millions here). Most snowmobiling takes place in rural areas, away from cities. Secondly, the temperature when snowmobiles are running is generally below freezing and the sun is low on the horizon in winter so ozone simply will NOT form. It’s a scientific fact.

So why do snowmobiles have to meet requirements that only really apply to high population areas in the summer?

Politics, again!
2-stroke snowmobiles do not contribute to worldwide pollution in a way that is remotely possible to be measured. But due to broader pollution concerns, politicians and bureaucrats have created rules that affect snowmobiles, much as they already affect automobiles, which due to their massive numbers and use in summer can impact the ozone.

However, when new regulations for snowmobiles were proposed, the OEMs decided to solve the problem with technology, when I believe they should have used lawyers and politicians to fight the battle first. The legal costs to avert unnecessary legislation would likely have been only a fraction compared to the millions spent by the Big 4 trying to solve a nonexistent problem with expensive technology.
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Yamaha’s Apex uses a high-horse fuel injected, liquid 4-stroke to create its power.
This happened before
Motorcycles went through the same problem cycle, but in their case the problem was real, they do run in cities in the summer, and they are a much larger part of the internal combustion engine pollution problem.

Rather than clean up the popular 2-stroke bikes, the manufacturers led by large Japanese firms, decided to take the easy way out and drop the 2-stroke in favor of heavier 4-stroke machines.

When the emission requirements showed up for snowmobiles, Yamaha, not surprisingly considering their motorcycle experience, took the motorcycle route, and built only 4-stroke sleds. Yamaha reasoned that like motorcycles all snowmobiles would have to switch to 4-stroke power, and they would become an industry leader with their already superior 4-stroke technology.

But unlike the motorcycle manufacturers, the snowmobile designers did not agree with the “drop the 2-stroke” philosophy. They felt there were too many advantages to a 2-stroke engine in snowmobiles to let it go. They also had a large experience base with this popular engine.

2-strokes have a large power to weight advantage, which is important in an off-road vehicle that requires flotation. Motorcycles run on hard surfaces so flotation is not an issue, therefore the heavier 4-stroke bikes were more easily accepted.

2-strokes are often easier and cheaper to fix, if there is an engine issue. A seized piston is normally less than $100 to replace and the owner can usually do it himself. Have a major engine breakdown with a 4-stroke and you can count on a repair bill of more than a grand, and chances are you need a certified mechanic to handle it. Granted, 4-stroke motors generally have fewer meltdowns and are more reliable for high-mileage use.
A good example of higher repair costs can be seen in motorcycle motocross racing where new rules allowed 450cc 4-strokes to compete with 250cc 2-strokes. All of a sudden repair costs went way up for a normal amateur rider because the 4-strokes were much more expensive to fix. The result was that entry fields were reduced by 40%, and promoters had to reintroduce 2-stroke classes to bring affordability back into the sport.
Fortunately for us, makers are taking a proactive approach with 2-strokes. Ski-Doo took the lead with 2-stroke technology, investing money in direct injection technology from its outboard engine division, to clean up its favorite lightweight power source.

With throttle body electronic fuel-injection, semi-direct port-injection and finally direct into the cylinder E-TEC injection, the 2-stroke engines are now not only cleaner, but also deliver much better fuel mileage than before. In many cases the E-TEC is as good, or better, than its 4-stroke counterparts. Where before, 10-12 mpg was considered excellent, 18-20 mpg is now being seen with direct injected 2-strokes.

2-strokes cleaner, leaner
The 4-strokes are still cleaner burning and better for the environment. But that gap has been reduced dramatically too.

With much improved digitally controlled oil delivery systems, oil consumption is way down with the new Direct Injected 2-stroke engines, and smoke formation is nearly eliminated. As always, the 2-stroke sleds are much lighter, which has a large influence on handling and the effort required to ride a sled all day.

The effort needed to ride a 2-stroke is evident to me every spring when we go out West to test the new models. These events usually take place in the mountains, the last couple of years near West Yellowstone.

Now in my late 60s, I have to pace myself. The schedule is pretty tough and it is made harder by trying to keep up with the younger hotdogs riding as hard as they can at times. We test 8 to 10 machines each morning and the same after lunch, for four or more days straight. We each get some time on each sled, but after a day or so, I usually find the one that is easiest to ride.

This year it was the Ski-Doo MXZ 800 E-TEC. To stay up with the hotshots, I quickly realized that I needed to latch on to the E-TEC, under the pretext of checking out its new high-tech r-Motion suspension. The new 800 E-TEC was light and responsive and I could ride it all day without tiring out like I might on some of the heavier 4-strokes.

That’s not only my opinion, I’ve had several riders tell me that they have sold their 4-strokes and ordered new 800 E-TECs. They were tired of their heavier 4-stroke snowmobiles and wanted to get back on a lighter 2-stroke machine to experience the improvement in handling a lighter sled delivers, along with the added fun factor of a quick revving 2-stroke engine.

The death of the 2-stroke engine is indeed much exaggerated, and a lot of the thanks should go to Ski-Doo and its Rotax engines. Many improvements also have been made by the American manufacturers with their EFI units in the past few years, and we suspect Cat and Polaris are on the cusp of offering even better, more fuel-efficient direct injected 2-strokes, like Ski-Doo.

The new Ski-Doo direct injected sleds are easy to drive and are bringing a new level of fun back into snowmobiling. There is no longer a question of 4-strokes totally taking over, although they obviously will continue to play a role, especially for folks wanting major longevity out of their machines.

The 4-strokes also are fantastic for cruiser sleds, long mileage and low maintenance trail sleds, hopped up turbo applications, two-ups, utility sleds and for use in many more models.

But, I feel that dealers or manufacturers without a quick-revving, light, 2-stroke snowmobile in their lineup are missing out on a lot of sales.
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A closer look at the numbers
There are advantages with both 2- and 4-stroke engines.

In summary, the lower horsepower versions of each engine uses less gasoline and long-term any 2-stroke will ultimately use more oil than a 4-stroke. So the longer you keep and use a 4-stroke, the more economical it becomes, based on oil use. 4-stroke engines, Yamaha’s in particular, are also much longer lasting powerplants and their reliability and longevity still cannot be matched by the 2-strokes.

What’s the difference in costs to operate?
American Snowmobiler used its own Real World test results from last season for miles per gallon for a Ski-Doo 800R E-TEC (17.2 mpg) and Yamaha Apex (15 mpg). These engine’s offer nearly equal power production.

We then called local dealers for their oil prices and compared the U.S. average premium fuel costs as of January, 2012, for both sleds. We used 5,000 miles for overall usage.
In brief, the 2-stroke E-TEC used a hair less gasoline over 5,000 miles, while the 4-stroke Yamaha used less oil, both in quantity and cost. (This compares the oil used for oil changes in the Yamaha vs. the injection oil constantly added to the Ski-Doo.)

Comparing the two, the Yamaha’s fuel/oil costs were $50 less for 5,000 miles. Add in an oil filter that the Yamaha requires after 500 miles and labor for doing the oil changes and we call the operating costs a wash.

The gains as far as cost of ownership of a 4-stroke would come probably after about 5 years. The real positives to owning a 4-stroke are the longevity of a 4-stroke engine and the overall lower maintenance needed and superior reliability of a 4-stroke.

2-stroke advantages
• Lighter weight aids handling (more engine power per pound)
• Quicker revving
• Lower up front costs (when comparing similarly targeted models)
• Less costly, easier engine to repair

4-stroke advantages
• More environmentally friendly (no injection oil being burned)
• Ease of use (no need to add oil during season, just turn the key and go)
• Less maintenance or repairs needed
• Engine longevity/durability (Yamaha cites examples of 4-strokes running 40,000+ miles)
• Engine reliability
• Strong, more consistent power band.
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