I would like to pipe my 05 400ex this summer and I will probally go full. I am just wondering what the best one would be? for power, sound (not to loud). so if anybody has any tips or suggestions that would be great.

 

i would go with hmf or trinity and jet it and put a k&n or another performance airfilter in it.

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06 rapotr 700r- myne
06 blaster to many parts to list - my bros
04 raptor 80 fmf pipe and K&n - little sisters

 

I put a slip on HMF Sport Series pipe on my wife's 2006 400EX and rejetted it. I also opened the back of the airbox lid.
I was very surprised at the amount of power and throttle response gained with just the slip on.
A full system would gain even more.