This whole project would be much easier in a scrambler chassis! How is he going to mate that engine/gearbox assembly to the shaft drive of the sportsman chassis??? While retaining the 4wd????? I would think it might be easier to modify some type of high performance belt drive 4-stroke engine from another source... such as a 4-stroke sled engine, or even a personal watercraft engine!
The polaris pwc 750 pumps out 140hp with the turbo!

 

his project, not mine, he wants a single cylinder engine, i dont think hes going to have it be 4x4, i think hes going to pull the shafts and differential out, i havent talked to him since wednesday, so, next time i do i'll ask him.

 

He should of just bought a Zuki in the first place.

 

he may want to have the 650 in it, but the top speed will be no different what so ever. The transmission is what will limit it the most to what kind of gains you get. I have a good basic understanding on how the clutch works, and if the clutch cheeves are not machined, or a new clutch is put in its place, no top speed gains are going to come from it, and if there is, it wont be as much as he may be wanting. and if he is spending all this money....why didnt he buy the 800?