My son has a 400ex with stock exhaust and air intake. I have considered installing and FMF pipe along with a K&N air filter. Does anyone have a better suggestion?

 

well the k&n filters may be the best flowing but they let in dirt, thats why i would reccomend a uni foam filter or a twin air (twin air come pre oiled). as far as the pipe, the fmf is a good pipe. slip ons are ok, but its just a whole lot better to get the full system (but dont get the power bomb, its just a waste of money).

but along with these mods u will have to get it jetted up for the extra air flow, its not hard if ur patient hahaha.

if its ALOT of power u want, go with the white brothers E series full system, there insanly big, but made more for racing and hit the wallet pretty hard too.

trust me, ur son will have bragging rights with this stuff

 

Thanks alot beastly good info..

 

You know I hear alot about K+N filters letting in dirt and I know i saw that test sheet about all the filters a time before saying K+N let in the most dirt. Welp I've used K+N filters my entire life and I have never had a single issue except better performance I mean seriously by the time the tiny bit of dirt that a K+N filter may or may not let in it's time for a rebuild or another wheeler.