just wanna know thanks.anyone ever try one on their kfx 400.

 

If you run it with the airbox lid on, it is unlikely to feel any power gain.
If you take the airbox lid off and rejet your quad you will feel a power gain, even with the stock filter.
I read on a website that aftermarket air filters on a stock quad made very little improvement.

A k&n is easier to clean and it is a better setup than stock.

If you are after power, start by removing the airbox lid and rejeting it. If you still want more spent the money on a pipe.