APR Catback Exhaust System for Audi S4/S5 (B9) | CBK0012

The APR Catback Exhaust System (CBK0012) is a comprehensive, high-performance solution for the Audi B9 S4 and S5. Unlike traditional catback systems, this is a "true" full system that includes downpipes extending all the way to the factory catalysts in the upper engine bay. Inspired by the routing found on high-output RS models, this system replaces the restrictive factory dual-pipe setup with an oversized 3.5" (91mm) center section, delivering verified gains of +10 HP and +12 FT-LBS of torque to all four wheels.

Crafted from mandrel-bent T304 stainless steel, the system features electropolished cast Y-junctions for smooth transitions and maximum exhaust velocity. To ensure a premium cabin experience, APR engineers integrated a Helmholtz resonator to cancel out drone without restricting flow. The rear mufflers utilize the factory electronic valve actuators, allowing the car to maintain a civilized tone during cruising while unleashing a bold, aggressive roar under wide-open throttle. The system is finished with quad 3.5" motorsport-style polished tips for a refined, high-end aesthetic.

Key Features:

• True Full System: Includes downpipes, midpipes, and rear mufflers, extending from the factory catalyst to the bumper.
• Verified Power Gains: Proven increases of +10 HP and +12 FT-LBS of torque at the wheels.
• RS-Inspired Routing: Dual 2.5” downpipes to 2.75” midpipes merging into a massive 3.5” center section for optimized flow.
• Drone-Free Acoustics: Integrated Helmholtz resonator cancels unwanted frequencies while maintaining a straight-through flow design.
• Valve-Controlled Sound: Fully integrates with OEM exhaust valve controls to dynamically adjust sound based on driving mode.
• Premium Construction: TIG-welded T304 stainless steel with a brushed finish and cast splitters for maximum durability.
• Complete Hardware Kit: Includes an upgraded tunnel brace to accommodate oversized piping and precision brackets for a perfect fit.
• Customizable Quad Tips: 3.5” polished, single-walled motorsport tips with the APR logo; tips are removable for future customization.

Technical Specifications:

Installation Instructions