Modding 400EX

[JoeTeamMayhem]

I'm a drag racer that's pretty much all i do when i ride, and i only ride on the sand. My g/f has an 05 400EX, she wants to get more serious about racing, and she is smart enough to handle any amount of power i give her. I have a good idea of what i want to do, and im pretty set on who im gonna have do all the machining. I'm just looking for some feedback about what some of you may have done, who did it, and how pleased you were with the results and dependability.

Right now the list is looking like this:

+1 on the intake valves.
Porting.
HD valve springs and keepers.
Custom regrind cam.
HD cam chain.
Most likely a forged 89mm piston (440)
8 plate clutch.
serious frame lightening.
+4 swinger.
NOS wet spray. (for when i wanna ride it)

The reason i am stopping at a 440 is i need a forged piston for nitrous. As far as i'm told the forged pistons stop at 89mm without the relocated wristpin...If anybody knows of a forged stroker piston HELL YEA!!!

[Black R/T]

crf450 cam chain. HD straight from the factory and its cheaper than a stock 400ex chain.

Web 9i if you can find one.

oh, and a 450r carb 4 sure.

[crixal]

if you don't already have an exhaust get a full system ct racing. amazing power gains.

[JoeTeamMayhem]

Yea we run the white brother's e series. I've had one on our 99 since we baught the quad new, and have never had to do anything to it but repack it a couple times, and we have always done well against similar quads with similar mods. I have always heard good things about the CT though too.

Thank you for the crf chain info i didnt know that! I'll look into the cam as well. The carb i am going to run is the stocker 39mm FCR off my yfz. I've heard they work well once you get then jetted correctly. I've got more needles and jets for that carb than i can keep track of so hopefully its not too big of a headache! Thanks guys anything else is appreciated.

You'll need stronger head studs if you dont want the top end gaskets to leak.

[trailrider894]

i would say 416 kit over 440 it is just faster and has a little more power than the 440. at least that is what it seems like to me. but it all depends on what kind of racing she'll be doing.

[morse250r]

my buddy has a 416 high comp and runs with or runs down a few 440s at the dirt drags he has no head work piston cam and 450r carb it is a runner for sure 440s have a lot of problems it seems and more added costs 416 is 80 over or id think about a 426

[trailrider894]

i agree about the 440 stuff. i liked the 426 i rode at the track two weeks ago. it was pretty good noticed it getting really hot though. but i still like the 416 more.

[lpmaster]

sounds like your going to be putting this motor through a lot of stress. definately get some arp oversize studs. i'd recomend a re-sleeve and 426 bore and then when it blows you'll still have room for the 440 bore. what kind of compression are you planning on running. you cant really have a fast quad off the bottle and expect to hold under the button. depending on how much your trying to spray. with such an aggressive cam like that web your going to want to keep compression up which is never a good thing for nitrous. BE CAREFUL. :D
sounds like a fun build tho. i'd love to ride it