99-04 Mustang GT 4.6L Cat Back Kit

The MagnaFlow Performance Exhaust 99-04 Mustang GT 4.6L Cat Back Kit is a complete exhaust system engineered to replace the factory components from the catalytic converter rearward on fourth-generation Mustang GT models. Built from stainless steel and featuring 2.5-inch diameter tubing with 3.5-inch polished tips, this cat-back kit delivers measurable gains in flow efficiency while preserving the street-legal compatibility your daily-driven Mustang requires.

The 2.5-inch tube diameter is matched to the displacement and airflow characteristics of the Ford modular 4.6L engine, maximizing scavenging efficiency without requiring internal engine modifications. Stainless steel construction resists rust and corrosion from road salt and moisture exposure, extending the lifespan compared to mild steel alternatives. The larger diameter and optimized bend radius reduce backpressure in the exhaust stroke, which translates to improved throttle response and horsepower recovery—typically 8–15 hp depending on tune and fuel octane. The 3.5-inch exits provide a purposeful aesthetic while remaining streetable for daily driving through residential areas.

This cat-back system fits 1999 through 2004 Mustang GT coupes and convertibles equipped with the factory 4.6L naturally aspirated engine. Installation is bolt-on; the kit connects directly to your stock catalytic converter without removing it, preserving emissions legality. The MagnaFlow name has established credibility in the performance exhaust market, particularly among late-model muscle car enthusiasts who balance power gains against noise regulation and longevity. Weighing 55 pounds, the complete kit is substantial enough to ensure quality construction without unnecessary bulk.