I still don't get how a 4 stroke engine is more powerful than a 2 stroke engine. The 4 stroke engine rotates the crankshaft 2 complete turns per cycle, while the 2 stroke engine rotates the crankshaft just one turn per cycle. Doesn't that mean that 4 stroke engine more powerful?

Lord_Digby

The only correct comparison below of 2 strokes Vs 4 strokes is that a 2 stroke can (in theory) produce twice the power of a 4 stroke for the same sized engine and the same revs. Try this site it's will help you understand. http://www.deepscience.com/articles/engines.html Other information can be found here http://en.wikipedia.org/wiki/Two-stroke_cycle The four stroke link is at the bottom of the page. Sep 23 07, 2:28 PM

Baloo55th

The four stroke turns twice per cycle, but there is only one power stroke per cycle. The two stroke turns once per cycle, but still has one power stroke per cycle. The power stroke on the four stroke engine has to carry the engine through an unproductive turn, which the two stroke doesn't. However, the charging with mixture is far more efficient in the four stroke cycle as there is a stroke devoted to it, and the same appplies to exhaust. The two stroke manages to combine things, but not altogether efficiently. The Wankel engine is the most efficient size for size - when it runs properly. The concept is brilliant - the technology isn't quite there yet. (The Wankel engine doesn't go up-down-up-down like the ordinary engines in most cars. It has a weirdly shaped cam-like piston that revolves in an oddly shaped chamber and seems to get all four strokes into one revolution because of the shaping. Trouble is, the seals wear out too quickly and the compression drops. Some day they'll get it sorted.) This is simplified, by the way. There are different types of two stroke - most of which aren't used in cars. In fact, hardly any two strokes are used in cars now. And fewer motorbikes, too. The types that used to be used were polluters of the atmosphere to a far greater extent than the four strokes because of their oil burning lubrication. They were used mainly to keep the cost down in production, and the weight too. Vehicles like the Trabant (derived ultimately from the pre-war Auto Unions) were among the last. In the UK, the only real users of two stroke were Trojan and Commer (diesel commercials), and manufacturers like Bond who used motor bike engines. Sep 23 07, 2:47 PM

bigponder

Saab used two-strokes up until the mid-sixties. http://en.wikipedia.org/wiki/Saab_two-stroke Sep 23 07, 11:04 PM