I put the 440 kit on my 02 400ex along with an edelbrock carb (forget the size) a hot cam and a white bros exhaust- the thing was a screamer- couldn't keep the front end down!

 

i had a 99 back in the day that got a 416 and finally a 440 kit. the whole package is what makes it...not just a piston. If you're going to keep the 400 then look for a carb, cam, piston, head port, and good exhaust. I ran an edelbrock carb, stage 1 cam, 440 kit, and big gun gun exhaust and thought it was great. I swapped out the big gun for a curtis sparks and the thing was a beast!! I had a local guy port my head which made the most difference and never changed the valves. It had no problem with raptors or banshees, stock ones, or any of the other 400s out there. I sold it for a 450 though. Don't think you can get that kinda power from a 400ex. Never had ANY reliability problems, and mine had tons of hours on it!!

 

New to the site. I just bought a 2000 ex with a wiseco 440 big bore, stage1 cam and exhaust. The head gasket is blown. I ordered a new gasket before I pull it apart. I suspect at least one stud has stripped because I can move the front left corner of head gasket with a screwdriver and oil and air blowing out there.

I hear different stories about problems with the 440 big bore kit. Should I have the studs retapped for larger studs and put it back together or go back to stock or smaller bore.

Thanks in advance for any advice/ experience.