Cat-Back Exhaust Kit - 99-04 Mustang 4.6L

The FLOWMASTER Cat-Back Exhaust Kit for 99-04 Mustang 4.6L is a bolt-on performance exhaust system designed to enhance engine efficiency and auditory feedback on fourth-generation Mustangs equipped with the 4.6-liter naturally aspirated V8. This cat-back configuration—meaning it begins after the catalytic converter—preserves emissions compliance while delivering measurable flow improvements through a 2.5-inch diameter tailpipe with 3-inch stainless steel tips, allowing exhaust gases to exit with less restriction than factory tubing.

The American Thunder design from FLOWMASTER emphasizes resonance tuning—the internal chamber geometry is engineered to produce a deeper, muscle-car character while the stainless steel construction resists corrosion and retains heat efficiency during sustained driving. The 2.5-inch piping diameter represents a practical balance: larger than OEM 2.25-inch stock exhaust but not so oversized that it compromises back-pressure control on naturally aspirated engines. Stainless steel tips maintain a natural finish that resists rust and discoloration, complementing both stock and modified Mustang exteriors. Installation follows the cat-back-only principle, requiring no modifications to fuel mapping, oxygen sensors, or emission systems.

This exhaust kit targets enthusiasts seeking a straightforward bolt-on upgrade for 1999–2004 Mustang 4.6L builds—whether daily drivers wanting improved engine breathing and sound character, or weekend track-day participants optimizing low-cost performance gains. The FLOWMASTER cat-back exhaust for Mustang delivers visible power gains through reduced restriction while maintaining full street legality and OBD-II compliance across most jurisdictions.

At 56 lbs, this complete system represents a compact, manageable upgrade suitable for home installation with basic hand tools and jack stands. The FLOWMASTER 817312 for sale at TacticalSurplusUSA delivers proven American Thunder exhaust technology backed by the brand's 30+ years of performance muffler expertise.