The FLO 633NB is a 5" downpipe back exhaust system by FLO-PRO for the 2008-2010 Ford 6.4L. It replaces your restrictive OE exhaust system from the downpipe back with a 5" mandrel-bent exhaust system. It does not include a muffler and is intended for the track driven 6.4's! This kit not only sounds great but will improve the torque, mileage, and throttle response on your 6.4L!