1999-2004 Ford Lightning and 2003-2004 Harley Davidson Edition TrucksThis valve cover breather assembly replaces the original oil fill cap found on the passenger side of the factory valve cover.  The base is CNC-machined from billet aluminum for precise fit, and the included silicone O-ring is specially designed to prevent oil seepage at the base of the breather.  The filter base is microfinished for surface protection and good looks, and is easily hand-polished to a mirror-like appearance.  The removable filter element is a high-quality reusable unit from S & B Filters, which is securely retained in the filter base by the specially-machined retention groove at the top of the base.The purpose of this valve cover breather is to vent unwanted accumulation of pressure in the crankcase, and to provide maximum circulation of ambient air in the crankcase to reduce oil temperatures.  The installation of this breather will contribute to increased engine oil life and reduce the possibility of failed engine seals resulting from excessive crankcase pressure.  This breather will reduce the effectiveness of the vehicle's PCV system, and it is not emissions-legal.The kit includes (2) tube plugs needed to seal the vent line between the air inlet boot & driver's side valve cover, which is recommended when the breather is installed.