Do you want a 2 stroke or a 4 stroke...? The Indians run Minarelli's on them...it's says P450, but it's the same as a P4 or a P6 engine which are very popular in Europe. The Broncco minibike's also used them. They are cool engines, 4 spd, 5hp, but they lack the bottom end tq...however they do run out pretty good. You can also look for 75cc or 80cc upgrade kits, such as Polini etc...They are expesnive but they haul arse...Sometimes you need a different bottom end with 48mm studs to run the big bore kits, but they are significantly more powerful...10-12hp etc...