Here is the REAL deal on these cyls. We just put a motor together with the Vito 421cc cyls and 4mm crank. The customer brought these to us and had us assemble it with NO porting. The bike has CPIs, stock carbs, and all the other bolt ons. He dynoed it at LS dyno and it made 65hp. Come on guys, this is a 421cc 4mm crank. OUR lil Play port motors with same setup easily make 65hp range with stock stroke! Our 4mm crank Play ports put MUCH more!!