Hi
A friend of mine is thinking of buying a 400ex and wants a lil more snap than a regular 400ex so what is the differance in reliability, durability,maintenance (You know the regular stuff) on a 416 or 440ex vs stock?

 

416, 426 are better for trail riding and longer distances... 440 makes more heat ive been told and does better on the track. i may be wrong but thats what ive been told.

 

My friends with 440's have had lots of grief. Gasget problems and they run hot.

 

I would skip out on the 440 kit. Reliability issues aside, they dont rev as quick as a 416 or 426 does with the piston kit mod alone.
I've ran many 416 and 426 kits and prefer the 426 personally to get the best of both worlds and keep reliability as close to stock as possible while picking up power in the process. Depending on what else you do to the engine ofcourse.