Mine had a bunch of holes drilled in it but the other day i went ahead and like cut about 50% of the lid off and left just enough to keep the filter from ratling around. The diference that made is now instead of barely pulling a wheelie in 2nd gear it can go over backwards with power alone (because of my 22 inch over aired tires 2nd gear is very steep). Probably had something to do with the fact that it was pretty rich before i did it and that helped to lean it out. Sure didnt help my low end though [img]i/expressions/face-icon-small-sad.gif[/img]

 

yup, gains...but nothing to brag about. you need to compliment with jetting and pipe. WB e-series is the way to go. instead of drilling holes i purchased the moto-force air-box lid. it has vents built in it and is clear so you can see the condition of your air filter. pretty trick...i wish they made one for my Raptor.

 

I bought the moto-force for mine also. Can't say that the difference was that big but it was noticable. After a few rides it cracked in a couple of places and wouldn't seal anymore so I just bought another stock unit, traced the vent holes from the motoforce onto it and cut them out.