I agree with RT...you can't go wrong with either the Tymar or Ford's AIS. I personally would stay away from K & N type filters in a diesel. Proper and frequent maintenance is critical with this type of air filter. And most don't know how or do it often enough to be effective. Just my two cents.My original point was the Tymar and the Ford Severe Duty AIS flow the most air WHILE offering the best filtration. I'll freely admit the K&N washable will flow more air - lets in a lot of dirt too. I'll even go on record and state that you can get a lot more airflow by just leaving the filter out altogether. In fact, you can just disconnect the cold air intake hose at the turbo. The issue is improved airflow over stock AND improved filtration. The Tymar has a 98% filtration ability and the Donaldson filter (Ford Severe Duty AIS) is ranked at 99.5%. Either of these filters will move enough air to get you to about 500HP. If you're producing more than that - you're probably not worried about blowing motors anyway.