my friend has a 400ex he right now has a white bros slip on and my other friend has a pro circut (cant spell it) ne way they both are looking a new exaust what do you think they should get any info will be greatly thanked o and money is not an object

 

Curtis Sparks's X-6 has the most power gain for a 400ex.

 

look

heres a good comparison of pipes for it. theres one with the single dyno and a black box that has all of the facts. i might go with the pro circut or big gun but ill see

if your friends just have slip ons try a new header for that pipe. it makes a diff.

 

i like those dual exhaust for the 400ex they are awesome but cost a lot.

 

LTE or looney dual exhaust claim to put out 6-6.5hp max. around 700 $ though