Catback Exhaust System | Audi B9 S4, S5 | APR

Overview

The APR Catback Exhaust System for the Audi B9 S4 and S5 is a complete, high-performance exhaust upgrade designed to improve power, sound, and overall exhaust flow. Drawing inspiration from the larger exhaust architecture used on the RS4 and RS5, APR replaces the restrictive factory dual-pipe configuration with a larger, optimized exhaust system extending from the catalyst back.

The system utilizes dual 2.5" (63.5mm) downpipes transitioning into dual 2.75" (70mm) midpipes before merging through a cast Y-junction into a large 3.5" (91mm) midpipe. This free-flowing design reduces restriction while maintaining proper exhaust velocity and incorporates an integrated Helmholtz resonator to help control unwanted drone without compromising flow.

At the rear, the system splits through another cast Y-junction into dual valve-controlled mufflers. The exhaust valves integrate directly with the factory OEM valve control system, automatically adjusting based on driving conditions. This allows for a more aggressive exhaust note under acceleration while maintaining a quieter, more refined sound during normal cruising.

The system exits through dual cast Y-junctions into a quad 2.5" (63.5mm) outlet configuration, finished with lightweight 3.5" (91mm) motorsport-style tips. The tips feature a polished stainless-steel finish and subtle APR branding.

Construction is centered around durability and precise fitment, with mandrel-bent T304 stainless-steel tubing, a brushed finish, and TIG-welded construction throughout. Precision-fit brackets, OEM-style slip clamps, and an upgraded tunnel brace are included to accommodate the larger exhaust piping and simplify installation.

With its larger-flowing exhaust architecture, integrated valve control, drone-reducing Helmholtz resonator, and premium stainless-steel construction, the APR system provides a significant upgrade in both performance and character for the B9 S4 and S5. APR reports gains of up to 10 HP and 12 ft-lbs of torque at all four wheels.

Details

• Complete catalyst-back system including downpipes, extending from the factory catalyst back.
• Performance gains of 10 HP and 12 FT-LBS of torque delivered to all four wheels.
• Premium T304 stainless steel construction with TIG welding for strength and durability.
• Optimized flow through dual 2.5” downpipes, 2.75” midpipes, and a 3.5” midpipe.
• 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 minimizes drone and enhances sound quality.
• Valve-controlled rear mufflers dynamically adjust sound based on driving style.
• Removable quad 3.5” motorsport-style polished tips with APR logo; optional styles available.
• Smooth transitions and straight-through components maximize performance by reducing restrictions.
• Strikes the perfect balance of power, sound, style, and quality for enthusiasts.
• Fully emissions compliant for worry-free operation.

Fitment