I ordered a 440 kit, rev box (XR 250), cam, valve springs, etc.. for my 400EX and was wondering about having the head ported and polished. Has anyone had this done? I have talked to two different places and one says there is tons of power to be gained ($375) and the other place said there isn't much there without spending BIG BUCKS! Any help is appreciated.

 

I did my own.It helps alot at top end. The intake and head are mismatched to begin with so they should be port matched. Why a 440 kit $$$$$ they are actually only 435 cc's and replacing the sleeve is alot more expensive than a bore. I bored the stock sleeve to 426 (1mm smaller) the piston kit only cost $100.00 and $35.00 to bore. the savings paid for most of the FCR carb and I have outrun 440 kits on sand mountain (Fastrax has witnessed this). Flow is more important at top end. What cam also determines the amount of port work done. a mid range cam wont respond well to a high end port. there will be no low end. I run the web cam 450-451 grind. 1 step smaller than a full race this cam responds well to porting. I run alot in the sand where I need the revs. I would at least port match the intake manifold to the head and check the exhaust pipe port alignment. Then do a 3 angle valve job this is definatly worth the price.


99 426ex , Web Cam, FCR carb, CT revlimiter, DMC exhaust, XCT's ,K&N, One kit,

http://www.trxoutlawz.com/

 

hey AIR you said you did your own work, even
the head work? my moter is beening worked on
right now , its beening bored to a 426, a cam
and a 3 angle port job. my ? is does it need to be port and polished.

 

The only thing I didnt do was bore the Cylinder and do the three angle valve job. I did the porting myself, I have 16+ years as a mechanic and have did some drag racing etc, all the same principles apply only in a smaller scale. Yes port it, at least match port the intake to the head, they are two diffrent castings and dont line up very well this causes swirling in the intake and reduces efficiency alot. to see what i mean pull the carb and feel around where they meet it will suprise you how poorly they line up. Porting and polishing will help the upper rpm range the most.

 

Hey guys,

What piston manufacturer are you guys using? So far Wiseco is the only one I can find in 3mm over but I've never been really wild about their pistons. Do you know if anyone else produces that size piston for the 400EX?

Thanks,

Dennis