EXCEPT Convertible. BORLA presents their exhaust systems for the Mustang EcoBoost equipped with Active Exhaust. Our 2.25" diameter Cat-Backâ„¢ systems include valves that retain the function of the Active Exhaust allowing you to change the volume of your exhaust by selecting different driving modes. The S-Type sound level delivers an aggressive sound without the drone and is tuned specifically for the 2.3L EcoBoost engine. This system features quad (2 per muffler assembly) 4" round bright chrome on T-304 stainless steel tips but is also available with black chrome on T-304 stainless steel tips. Cat-Backâ„¢ Exhaust System Active Exhaust Valves S-Type Sound Level No-Drone Bolt-On Installation 4" Round Bright Chrome On T-304 Stainless Steel Quad Tips T-304 Stainless Steel Construction. Each BORLA Exhaust System is built from premium T-304 austenitic stainless steel to give you the absolute best in performance and durability. Ultra-smooth mandrel bends ensure maximum flow & power and precision computer numerical control (CNC) manufacturing ensures an accurate fit. Best of all BORLA stands behind every system with a Million-Mile Warranty. Just what youâ€d expect from the worldâ€s most experienced (and most winning) exhaust brand.