Two Stroke Engines
     The two stroke engine is the main reason why PWC's are being banned around the nation. It isn't the most technological of engines and is the main reason why PWC manufacturers use them. The animation shows a 2-stroke engine in action.

     The advantages of a two-stroke engines are: they are lighter, simpler and less expensive to manufacture. Two-stroke engines also have the potential to pack about twice the power into the same space because there are twice as many power strokes per revolution. The combination of light weight and twice the power gives two-stroke engines a great power-to-weight ratio compared to many four-stroke engine designs.

There are four main disadvantages with a two-stroke engine:
  • Two-stroke engines don't last nearly as long as four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear a lot faster.

  • Two-stroke oil is expensive, and you need about 4 ounces of it per gallon of gas. You would burn about a gallon of oil every 1,000 miles if you used a two-stroke engine in a car.

  • Two-stroke engines do not use fuel efficiently, so you would get fewer miles per gallon.

  • Two-stroke engines produce a lot of pollution -- so much, in fact, that it is likely that you won't see them around too much longer.

     The main problem of the four disadvantages is the pollution. If you look closely at the animation, you can see that after the firing of the spark plug the reed valve opens to let in new gas/oil/air mixture. When the valve opens you can see the piston has not fully sealed up allowing that fresh gas/oil/air mixture to be released into the exhaust and eventually in the water without being fully burned off. Tests have been done on Jet Skis and it has been calculated that in two-stroke jet skis (newer jet skis are 4-stroke and burn fuel more efficiently) that in a two hour ride, one ski can dump four gallons of fuel into the water. That is a lot of fuel that enviromental groups, such as The Bluewater Network, are trying to fix.

     Nearly half of the national parks have banned jet skis and many parts of the United States have banned them as well. There are emmission regulations that PWC manufacturers have to abide by in order to sell their skis in certain states. California at the moment cannot sell any new "Stand-up" jet skis due to their poor emmissions.


All information taken from "How Stuff Works"

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