Originally Posted By: MostlyHarmless
Originally Posted By: Arney

Another old technology that I always wondered about was the good ol' two-stroke engine.


Hopelessly inefficient and polluting, compared with modern 4-stroke engines, be it diesel or gasoline. Even modern two-stroke are way, way, way behind.

The ONLY benefit of good ole' two-stroke (or modern two stroke) is the weight versus effect ratio. They are simple machines that can be made ligther and cheaper than 4-stroke equivalent. Which is why you find them on motorcycles, snowmobiles and small boat engines.

Recent advances has cut into the niche of two stroke engines. Four stroke for motorcycles are old news. Four stroke outboard boat engines and snowmobile engines are getting more popular and gaining their market share.

Some benefits of four stroke: Much more silent, lower fuel consumption and you have a lot of more torque (moment) at slower speeds (meaning the engine can run slower and still push the boat/snowmobile). The drawbacks are usually higher weight, more complex engines and a higher price.

Direct-injected 2 stroke engines can be made nearly as clean as a 4 stroke engine. Current direct injected 2 stroke outboards pass all the same emissions that the 4 strokes do, they use no more gas than the 4 strokes do, and they weigh less. The only problem with modern 2 strokes is they are stuck with the reputation they have earned as dirty oil burners.

Around here anyways, nearly all the tournament fisherman use 2 strokes still, simply because they are lighter(in turn faster) and get just as good of mileage as the 4 strokes.

As for 4 strokes taking over in dirt bikes, that has as much to do with politics (and 2 stroke reputation) as it does with anything. The 4 strokes are easier to ride, and therefore most riders can ride harder for longer with the 4 stroke. On the other hand, 2 strokes have better power to weight ratio, and a talented rider will be faster on them (notice the freestyle guys still use 2 strokes). The big problem there is the 4 strokes are more expensive/time consuming to own and maintain than the 2 strokes were.

If someone were to spend the time and money on 2 stroke engine technology that has been spent on 4 stroke engines, they would absolutely be as clean, get as good of mileage, and have a better power to weight ratio. I wouldn't count on it happening though.