Tell me how to get my 400ex to a 416ex please.
any suggestions.

 

Well..... hmm, Id start by ordering a 416 kit. (oversized piston, rings ect)
Take your motor apart.. (dont think I recommend YOU do this) take your cylinder to a machinist,
along with your new piston... tell him to bore and hone the stock sleeve to fit the 416 piston.
assemble the motor... wallah. BUT, you wont hardly feel this power improvement.
With a 416, you need to go all the way. Race cam, springs, high compression, ect. Then you will have a faster EX.

 

Well nothing else i can add to that mr350x.

Chewy it costs hella $$ to make a nice 416. Instead you can bore to a 440 and put a cam in for like 600-800(i think) and be ALMOST as fast. I toast 440s all the time because they are not fully built.