im thinking about boring my 400ex. my friend got the yfz450 and hes planning on modding soon so i want to be able to run close with him. i was wondering where a good 416 or 440 kit could be purchased. thanks a bunch

 

call C&D. the # is 308-696-7805

you will want a good cam to go with the piston.

 

Find out exactly what you would need and then get it off ebay. A 440 kit (piston, cylinder sleeve, rings, clips, etc.) from Wiseco runs $170. You will want to replace your head gasket as well. I am not sure what else you will need. You must also run premium gas in the 440 kit but regular is fine for the 416. Just making sure that you know if you don't already. I have heard that the 416 or 426, most say the 416 kit, is the way to go.