the fmf powercore 4 pipe is horrible sounding i heard it on a friends 400ex and on a rappy they sound just bad he then got a whitebrothers e series slip on for his 400ex and gained tons and tons of top end power over the fmf and it sounds good.

 

hmf would be your best bet and for the header i would grind out your stock welds hmf has good sound isnt to loud but is awesome in power

 

check CTracing.com their pipes make the most power and use an adjustible disc-type silencer much like the white bros. personally i think it looks better too. i think a full kit UNI jets header and muffler is around $525. ill be gettin one for graduation in about 3 weeks along with holeshots new wheels and shocks. any suggestions on shocks for a guy that rides mostly trails and some mx. keeping price in mind!

 

i say get the pulsecharger pipe,thier getting the most hp and with no loss in hp when the stealthcore is put in

 

The best sounding exhaust IMO on the 400ex would be a Big Gun exhaust but I dont know how the power gains are with it.

 

anything but big gun i personaly love my yoshimura

 

yoshimura is excellent but curtis sparks is the best you can buy check out there site at "sparksracing" to look at there pipe
the x-6 is good there pipes cost a lot though but ur paying for the best
believe me
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Are you only interested in sound or performance too? We use to own a 400EX and we put a Big Gun exhaust on it. It was good for low-mid range performance.

 

I have to agree with the Curtis Sparks. That is probably the best on the market. I personally have the W/B R Series on mine with the Header. Not many have this one because it's a pain to jet it right. I actally lost power when I first put it on because it needs LOTS of air and fuel , so I changed the rev box, added 8 1" holes in the airbox lid, changed and raised the needle, and went from a 148 to a 165 main. It took about 3 months of playing with (swapping jets about a dozen or so times), but it's right now. In a staight line drag, it'll beat anything with the same mods except a well jetted Curtis Sparks. If their jetting is off, they can forget it. Better pickup than a stock Raptor, beats stock Banshees and some with pipes, even a preditor. I love my R series, but the Curtis Sparks would be on my next if I did it over again. But then again, the sound of Delilah (my quad) when she gets on the pipe gives me the chills!