agree with the above 2 statements-

every time that plug fires and slams that piston down, it's destroying that bushing and all the parts connectedto it more & more- that would cause a knocking sound for sure. do it right, you don't want to worry about that every time you start it up...

 

As far as going bigger, you have 2 choices for pistons that don't involve having to sleeve the cylinders. 715cc or 730cc. You will have to have the cylinders bored. Don't go crazy with high compression. 12:1 is about as high as I would go. You may run into headgasket failure issues with the higher compression ratios.

There are several companies out there selling big bore kits for these motors. Big Kev's Performance and Four Stroke Tech to name a few. If you have it torn down this far, I would change out the cams also.

As far as exhaust goes, if you have your heart set on duals, LTE's are the best performance wise but they are loud and won't meat most states noise requirements. Probably the best exhaust system out there for the V is a Muzzy Super Pro 2 into 1 system.

Good Luck with it.