Best exhaust for 400ex

[Colt Gibson]

I'm looking for a S/O exhaust with the most gain, more so in bottom end performance, i have a stock 05 400ex, so far i heard the HMF and the white brothers exhaust is the best for the 400, so if anyone can help i'd appreciate it, also what should i jet the carb to.

[4TraxRider]

Do a search, the topic has been covered at least 100 times, but any reputable exhuast makeer will produce close to the same numbers. Stay away from certain DG's, all cobra's and anything that seems way to cheap to be good. HMF, White bro's, FMF, Pro-circuit, Sparks are all great manufacturers.
The jetting is going to depend on where you live, and elevation. Many times the exhaust you get will let you know a good size jet to start with and experiment from there. If it helps, i used to run a 165 main with the needle on the 4th clip, with no airbox lid when i used to have a 400.