Originally Posted by Jinksy
Has anyone used Filtered Air Box Vents after drilling holes in there air box? If so, how did it effect the performance?
I doubt the difference in performance will be noticeable unless you also add a programmer and a free flowing exhaust. You can probably spend $750 and get 1-2 hp max. Motocyclist had a CBR250r that they decided to take racing in the 250cc street class. After a complete engine and suspension overhaul it was able to keep up with the slightly modified ninja 250s that most everyone else in the class was running. Considering your CRF has the same engine with different tuning you can do a lot to the engine but I doubt you'll get much out in return. I'd check the CRF250 thread see what mods others are doing for power. I'm pretty sure the gearing change will have the most bang for the buck.
Also as you add holes to the airbox, you increase the chances of it ingesting water.