Ford Racing Performance Parts 2005-2010 MUSTANG GT - MUFFLER KIT (50 STATE) Standard on the 2007-2008 Shelby GT & GTH 50-States drive-by noise legal Note: 409 stainless exhaust material is titanium stabilized ferritic stainless steel. 409 stainless is used in applications where appearance is a secondary consideration to mechanical properties and corrosion resistance and where some weldability is required. An example of 409 stainless usage is catalytic converter assemblies. 409 stainless has excellent forming characteristics and is rust through resistant. A surface rust will form in most instances. This rust retards further corrosion.