well i am officially back to riding red!! i was lead astray after riding(racing) hondas for years. i was tricked into buying a polaris!! lol
anyways i have a 400 ex and want to make it a little faster. i was thinking about white brothers e series, uni filter, and rejet. is this worth my time?? also when i re-jet i will just need to change main jet right?? thanks

 

The E series is a good pipe as are some others. Any time the airflow, either in or out, is improved the fuel/air mix must be compensated for. So, yes, you will need to fatten up your main jet circuit; possibly by 2 full sizes, depending on your elev. or other alterations planned. Of course, the only way to know what YOUR particular engine wants is to ask it by testing & reading the plug.As you know the E series silencer, like the Supertrapp, is tunable. The number of discs you run will determine the part of the band that it will improve. The more discs, the higher in the band the improvement will appear. Also the fatter main jet you'll need.