Dynomax 38517 VT Muffler Cat-Back System DynoMax Valve Technology Mufflers feature an exclusive, precisely calibrated internal valve that redirects exhaust flow, during cruising conditions, to provide Drone-Free Performance. Hammer the gas and the valve automatically adjusts for maximum exhaust flow, delivering on-demand performance and a deep, throaty drone-free sound. Exclusive Dynomax Valve Technology DRONE-FREE Performance. On demand performance and sound Straight through welded design