what would be best for my 400ex all i am going to get is air fliter and jet kit so would the x-4 be the best for my aplication and where is the cheapest place to buy it and not ebay i've checked

 

it depends, if you want a lot of bottom end then go with the x4, but if you want pretty much the same bottom end and more top end then go with the x6, they are almost identical except the x6 has just a hair less bottom end and more top and vice versa for the x4. I would check motojoe.com, ronnies.com or any other big aftermarket companies. look through some mags for ads.

 

i run the x-6 and my buddy runs the x-4. both are simlar. the x-6 is better at high rpms, mainly on a built bike. i wouldn't hesitate buying the x-4. it opened my buddies up a lot. i would also look into lrd or hmf. i would call C&D racing. the # is 308-696-7805. these prices will be cheaper than directly through the company. lrd sets their prices and distributors can't change that but i think you can get free shipping from C&D on that pipe.