I belive that the range of the engine is up to 50 in 2 stroke and 72 in for stroke. If you want a really good 2 stroke pick the west 50 of if you want a really good 4 stroke pick the YS 63. if you cant get the ys then i think that the sito has the best power to weight ratio out of all the 70 4 strokes. It really depends on what you want from the model if you want to prop hang and TR all day then you really need a 4 stroke because of the mid range power and because of the tourque. If you want to fly it around normally (what ever that is) then pick a 2 stroke. A lot of the engine choice is down to money i guess. If it was me then i would get the sito 72 because it is really nice engine. Also there is somthing about the sound of a 4 stroke in the prop hang, 2 strokes just always seem to sound as if they are stugling because all they do is scream.