Originally Posted by pbonsalb
The bottom side probably looks great. If you change one of these filters and study the intake box, you will see how debris collects on the top, but falls off on the sides and does not collect on the bottom. And as air filters go, the used stock one in the picture is not bad or clogged up enough to cost 15 hp.
The top is the clean part! The bottom of the filter it was grimy. I'd say 15-20% of the filter was blocked.
Obviously, it sounds better and is a little more responsive. I'm not saying it's because of a K&N filter but a filter that is not clogged.