yeah i have a 06 trx250ex im lookin to put some performance mods on it like exhaust and stuff like that..

please give your best knowledge on this concept

 

Bottom line the more air you can get into your motor and out of your motor equals more horse power as long as the air fuel mixture is correct.
If I had a stock bike I would add an after market pipe a better breathing air filter like a K&N and an outerwaer and a dynojet kit jet it correctly and possibly some gearing changes this will help get you better throttle responce and more power and also more top end speed.
Hope this helps.

 

by boii put a hmf full system it gave it good power and it sounds good then get a k and n ,a jet kit and a rev box ur bike will b rippin and take off ur air box lid