The K&N cone filters aren't the problem it was the way the drop in filter wouldn't seal around the edges that have dusted so many diesels. If you want the very best filtering element than go with the Ford AIS system = $200 from powerstrokeshop.com, it will flow about 30% more air over stock and even more if you do the Zoodad mod, if you want the very best airflow than go with the AFE StageII. I didn't want the extra noise you get from a open element filter, so the AIS was the best choice for me. The AIS/Zoodad/BTM combo flows all the air my truck needs.