RE: someone please explain difference between 2 and 4 strokes..
Marshall,
From your explanation, one can understand that a four-stroke is always more powerful than a two-stroke engine.
Also, it is stated that a two-stroke engine will always need higher RPM levels, to achieve maximum torque.
Nothing can be further from the truth.
The design of any two-stroke engine places the ports, so they are timed to be effective at a certain target RPM range.
Even after it is built, it is possible to reverse-engineer an engine, changing its running characteristics completely.
Most larger two-strokes are timed to be at their best between 5,000 and 7,000 RPM.
Honda produced a four-stroke, inline six cylinder, 250 cc engine ([link=http://world.honda.com/goodwood/machines/rc166/]RC166[/link]), that was timed to be at its best power between 16,000 and 18,000 RPM...
Dropping the sleeve (and raising the head appropriately), would shorten the intake and the exhaust duration, improving the low RPM torque at the expense of high RPM performance. This would make a .40 spin a huge, 15x8 prop, at lower RPM...
Raising the sleeve (and dropping the head appropriately), would make a normal sport .40 get to 30,000 RPM, like a pylon engine...
These are examples and much more subtle changes are also possible. Changes require more changes; for higher RPM, the standard bearings must be replaced, for example.
There is always a trade-off. It would be quite costly to make an engine that is at its best everywhere.