APR Valved Cat Back Exhaust System

The APR Catback Exhaust System for the Audi B9 S4 and S5 is a complete high-performance exhaust solution, running the full length of the vehicle from the catalyst back. Inspired by the larger centre-pipe design found on higher-output RS4 and RS5 models, this system is engineered to deliver increased performance, an aggressive exhaust note, and a striking visual upgrade.

Designed and manufactured using premium materials and advanced production techniques, the APR Catback Exhaust System is built to withstand harsh conditions while delivering long-term reliability. Under wide-open throttle, expect a bold, aggressive growl, along with gains of up to 10 horsepower and 12 ft-lb of torque delivered to all four wheels.

Unlike conventional catback systems, the APR design extends all the way to the factory catalyst located in the upper engine bay, making this a true full-system upgrade. Exhaust restrictions are minimised through smooth transitions, oversized piping, and straight-through mufflers and resonators. The system is constructed from mandrel-bent T304 stainless steel with a brushed finish and TIG welding throughout, ensuring exceptional durability and a premium appearance.

Inspired by RS performance models, the exhaust routing has been completely reengineered. Dual 2.5-inch (63.5 mm) downpipes transition into dual 2.75-inch (70 mm) mid-pipes before merging through a cast Y-junction into a large 3.5-inch (91 mm) mid-pipe. This replaces the restrictive factory dual-pipe design and incorporates an integrated Helmholtz resonator to minimise drone without compromising exhaust flow.

The system then splits again via another cast Y-junction into two rear, valve-controlled mufflers featuring advanced sound absorption technology. These valves integrate seamlessly with the factory exhaust control system, opening under aggressive driving for enhanced sound and closing during cruising for refined comfort. Exhaust gases exit through quad 2.5-inch (63.5 mm) outlets, finished with lightweight, single-wall 3.5-inch (91 mm) motorsport-style tips featuring a polished stainless finish and subtle APR branding.

Precision-fit brackets, OEM-style slip clamps, and an included upgraded tunnel brace ensure a straightforward installation while accommodating the system’s oversized piping.

• True full-system catback design extending to the factory catalyst
• Mandrel-bent T304 stainless steel construction with brushed finish
• Integrated Helmholtz resonator for reduced drone
• Valve-controlled rear mufflers with OEM integration
• Quad 3.5-inch (91 mm) polished stainless steel exhaust tips
• Includes upgraded tunnel brace and OEM-style mounting hardware

• Complete catalyst-back system including downpipes, extending from the factory catalyst rearwards
• Performance gains of 10 hp and 12 ft-lb of torque delivered to all four wheels
• Premium T304 stainless steel construction with TIG welding for strength and durability
• Optimised flow through dual 2.5-inch downpipes, 2.75-inch mid-pipes, and a 3.5-inch mid-pipe
• Mandrel-bent brushed piping paired with electropolished cast splitters for a refined finish
• Precision brackets and slip clamps ensure accurate alignment and hassle-free installation
• Includes an upgraded tunnel brace to accommodate the larger piping
• Integrated Helmholtz resonator minimises drone and enhances sound quality
• Valve-controlled rear mufflers dynamically adjust sound based on driving style
• Removable quad 3.5-inch motorsport-style polished tips with APR logo; optional styles available
• Smooth transitions and straight-through components maximise performance by reducing restrictions
• Strikes the ideal balance of power, sound, style, and quality for enthusiasts
• Fully emissions compliant for worry-free operation

• Brackets: Precise
• Brand: APR
• Category: Exhaust
• Clamping type: Slip clamp
• Clamps included: Yes
• Emission code: 5
• Exhaust tip colour: Polished
• Exhaust tip diameter: 3.5 inch
• Exhaust tip finish: Carbon fibre with brushed inlay
• Exhaust tip quantity: 4
• Exhaust tips removable: Yes
• Finish: Brushed
• Main piping diameters: 2.5 inch, 2.75 inch, 3.5 inch
• Muffler finish: Brushed
• Muffler type: Helmholtz, sound absorption
• Pipe bend type: Mandrel
• Pipe material: T304 stainless steel
• Product type: Exhausts (catback systems)
• Sub-category: Exhaust and tail pipes
• Tail pipe outlet outside diameter: 2.5 inch
• Tube connection: Butt joint
• Valve included: Yes
• Valve type: OEM
• Welding: TIG

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General Notes:

• If installing this system on a coupe, you will need to cut ~59mm off from the front Y-section of the exhaust.