Fits 2011-2014 Mustang GT 409 aluminized stainless steel corrosion-resistant muffler body construction with polished 304 stainless 4" diameter tips Mufflers were standard on 2011-2012 Mustang Shelby GT500 Throatier exhaust note 50 state 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.