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400ex porting questions -help-

5K views 6 replies 4 participants last post by  glockovets 
#1 ·
hi I tore down my 400ex motor after about 7 years of abuse... everything looked good in the head and overall it was pretty clean. I want to bore it to a 416 kit and get the head ported for more power, does anyone know of a really good builder/shop to take this to? I live in tampa and local is better but i can send it out anywhere if needed. Looking for more overall power from the beast but i heard the 440 bb kits are unrealible... :confused: Anyway if anyone has any thoughts or suggestions please post them. Just want to beef her up alot in a semi-inexpensive way. :lifting:

Also going on is: new race frame(old one cracked), +2 jb swinger, g-force adj. axle and currently it has white bros pipe,k&n filter,and front and rear holeshots.
 
#4 ·
I don't own a 400EX, but I have also heard that the 440 kits are unreliable. I don't know the specifics, but maybe they aren't changing the head bolts.
 
#6 ·
Well I would do it but after my disasteroous mistake with mine (Not the Porting) I would be reluctant to do anyones but mine. I ported my head a few months ago and just got around to putting it on this past weekend. All I can say is it was a mean SOB for about 5 min..lol, but disaster struck. I re installed the valves that came out of it thinking they would be ok boy was I wrong! I lost a head piston and jug because i was to cheap to buy new valves! but it's really not that difficult with the right tools and to do it perfect takes practice and a flow bench with out the bench your basically doing it from feel.
 
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