It all has to do with differnt manufactures thinking when designing the engine, its all about the control of the gasses, turbulence, and speed of combustion, theres alot to the workings of a 2 stroke head. Theres been many differnt designs, some have advantages over others, some have disadvantages over others. I would suggest buying a 2 stroke book and study all the differnt kinds of designs and thier properties if your a information junkie...LOL