Upgrading your 2020 Audi S4 with a high-performance exhaust system is one of the most rewarding modifications you can make. Beyond the immediate improvement in sound, a properly installed exhaust can unlock additional horsepower, reduce weight, and sharpen throttle response. However, the installation process demands attention to detail to avoid leaks, drivetrain issues, or poor fitment. This guide expands on the basics, offering advanced tips and techniques to ensure your exhaust upgrade delivers maximum performance and longevity.

Choosing the Right Exhaust for Your 2020 Audi S4

The 2020 Audi S4 features a 3.0L turbocharged V6 (EA839 engine). Its exhaust layout is complex, with a single exhaust path from the turbo that splits after the downpipe. When selecting a system, consider these key factors:

System Types: Cat-Back vs. Axle-Back vs. Turbo-Back

  • Cat-back replaces everything from the catalytic converters rearward. This is the most common upgrade for sound and modest power gains (5–15 hp) without requiring a tune.
  • Axle-back only replaces the rear mufflers. It changes sound but offers minimal performance gains. Often chosen for a subtle tone without modifying emissions components.
  • Turbo-back includes downpipes, eliminating the stock catalytic converters. This yields the largest power gains (20–40 hp with a tune) but is illegal for street use in many regions due to emissions laws. It also requires ECU tuning to avoid check engine lights.

Material and Construction

  • Stainless steel (304 grade) offers excellent corrosion resistance and durability at a moderate price. Most aftermarket systems use 304ss.
  • Titanium reduces weight by 40–50% compared to stainless steel and produces a distinct, higher-pitched exhaust note. It is significantly more expensive but ideal for track-focused builds.
  • Mandrel bending ensures smooth internal diameter vs. crush bending, which restricts flow. Confirm the system uses mandrel bends for maximum performance.

Sound Preferences

Listen to online clips of different brands for the 2020 S4. Some systems (e.g., AWE, Milltek) are designed for a refined, drone-free tone. Others (e.g., Armytrix, Fi Exhaust) offer adjustable valves to switch between quiet and aggressive modes. Consider whether you want a resonated or non-resonated mid-pipe – resonated reduces drone but may soften top-end volume.

Tools and Equipment: Beyond the Basics

While the original list covers essentials, a professional-grade installation requires additional items. Gather these before you start:

  • Torque wrench (ft-lb and in-lb) – critical for accurate clamping forces on exhaust flanges and downstream O2 sensor bungs.
  • Exhaust hanger removal tool – pry-style or hook-style tools make removing stubborn rubber hangers much easier than using a pry bar.
  • Anti-seize compound – apply to threads of all bolts and O2 sensor bungs to prevent seizing from exhaust heat.
  • Penetrating oil (e.g., PB Blaster or Liquid Wrench) – spray bolts and hanger studs the night before to reduce breakage risk.
  • Deep sockets (14mm, 15mm, 16mm) – needed for exhaust manifold studs and downpipe bolts.
  • Oxidative torch or heat gun – helpful to loosen corroded bolt connections on the downpipe flange.
  • Gasket sealant (high-temp RTV) – optional for sealing flanges if new gaskets are not included.
  • Safety wire or zipties – to temporarily hold hangers while aligning the system.

Preparation and Safety Essentials

Work on a level, well-ventilated garage floor. Use jack stands rated for at least 3 tons – never rely solely on a hydraulic jack. Chock the rear wheels, and let the engine cool completely (exhaust components can exceed 600°F after a drive). Wear thick mechanic's gloves and safety glasses; hot oil or rust flakes can cause injuries.

Pre-Installation Inspection

Before removing the stock system, inspect the entire underbody for rust, corrosion, or damaged hangers. Spray all exhaust fasteners with penetrating oil and wait 15–20 minutes. Inspect the downpipe-to-turbo junction – the 2020 S4 uses a V-band clamp that can corrode. If the clamp looks seized, consider replacing it with a new OEM clamp.

Step-by-Step Installation Walkthrough (Advanced)

1. Removing the Stock Exhaust

Start at the rear: unbolt the axle-back section first, then work forward. Support each section with a jack or helper before removing hangers. For the downpipe, you will need to access the V-band clamp from underneath – a long extension and swivel socket help. Be prepared to wrestle the downpipe out past the steering rack and front subframe. On the 2020 S4, loosening the transmission heat shield (two 10mm bolts) gives you more room.

2. Dry-Fitting the New System

Before tightening anything, loosely connect all sections with clamps and hangers. Adjust the position of each piece to ensure equal gaps around the heat shields and no contact with the driveshaft or rear differential. The S4's exhaust tunnel is tight; give at least 3/8 inch clearance to all moving and hot components.

3. Tightening Sequence and Torque

  • V-band clamp: Follow manufacturer spec (typically 18–22 ft-lb). Over-tightening can warp the flange.
  • Mid-pipe to downpipe flange: Use new gaskets and tighten bolts in a star pattern to 20 ft-lb.
  • Axle-back connection: Use a slip-fit clamp; tighten to 30–40 ft-lb but avoid crushing the tube.
  • Hanger studs: If your system uses bolt-on hangers, apply threadlocker (blue Loctite) and torque to 15 ft-lb.

4. O2 Sensor Reinstallation

The 2020 S4 has two O2 sensors: one in the downpipe (pre-cat) and one after the secondary catalyst. When transferring sensors to the new downpipe, apply anti-seize to the threads and torque to 25–30 ft-lb. Do not over-tighten – O2 sensor threads are fragile. If the new downpipe lacks a bung for the second sensor, you may need a weld-in bung or a spacer (defouler) to avoid a check engine light.

5. Final Checks and Test Drive

  • Start the engine and listen for exhaust leaks – use a damp cloth over the tailpipes to create backpressure and amplify hissing sounds.
  • Check exhaust tips for centering in the bumper cutouts. Adjust hangers or clamps if the tips sit crooked.
  • With the engine warm, check for any burning smells as new components outgas machining oils (normal for first 10 minutes).
  • Test drive for 10–15 miles, then recheck all bolts and clamps while the system is hot. Retighten V-band and flange bolts after the first heat cycle.

Tuning and ECU Considerations

A cat-back exhaust alone does not require a tune. However, if you install a downpipe with a high-flow or catless configuration, the ECU will trigger a P0420 code due to reduced backpressure. A stage 2 tune or using a sensor spacer can resolve this. Brands like Integrated Engineering, APR, and Unitronic offer tunes specifically for the 2020 S4. For maximum gains, combine a downpipe with an intake and intercooler upgrade, then have the car dyno-tuned.

Maintenance and Longevity

High-performance exhausts are low-maintenance, but a few steps extend their life. After installation, drive the car for a week and re-torque all connections. Annually, inspect for:

  • Clamp slippage – if the system shifts, it may contact the underbody.
  • Rust or pitting on stainless steel near weld joints – rare but possible in salt-belt regions.
  • Hanger degradation – silicone or polyurethane hangers last longer than rubber. Replace rubber hangers every 2–3 years.

If you drive in harsh winters, consider applying a ceramic coating or high-temperature paint to the downpipe to prevent surface rust. For titanium systems, avoid contact with brake fluid or road salt, which can cause discoloration.

Sound Characteristics and Break-In

Expect the exhaust note to change over the first 200–500 miles. Fresh packing material in mufflers and resonators may settle, producing a slightly louder and deeper tone. During break-in, avoid sustained high-RPM operation for the first 50 miles to allow gaskets and sealing surfaces to mate properly.

Reducing Unwanted Drone

If you experience resonance at highway cruising speeds (1800–2200 RPM on the S4), consider these solutions:

  • Add a Helmholtz resonator or J-pipe (some systems offer these as add-ons).
  • Fabricate a additional hanger near the center of the system to change vibration modes.
  • Use a resonated mid-pipe section instead of a straight-through design.

Common Mistakes to Avoid

  • Skipping new gaskets – always use new OEM or supplied gaskets. Reusing compressed gaskets guarantees leaks.
  • Over-tightening slip-fit clamps – this deforms the tube and causes leaks. Tighten until the clamp engages firmly, then add one quarter turn.
  • Ignoring hanger orientation – some aftermarket hangers are designed to rotate. Align them so the rubber hangs straight, not twisted.
  • Forgetting the ECU adaptation – after installing a full turbo-back, drive the car for 20 minutes in varied conditions to allow the ECU to relearn fuel trims. If a CEL appears, clear codes and retest.

External Resources and References

For additional guidance, consult these authoritative sources:

Performance Gains Summary

Below is a realistic estimate of power gains for a 2020 Audi S4 with a proper tune and supporting modifications:

  • Cat-back only: 5–12 hp, 8–15 lb-ft
  • Cat-back + intake: 10–20 hp, 15–25 lb-ft
  • Cat-back + downpipe + stage 2 tune: 30–50 hp, 40–70 lb-ft
  • Full turbo-back + intercooler + E85 tune: 60–80 hp, 70–90 lb-ft

These numbers are based on dyno results from reputable tuners. Individual results vary based on fuel, altitude, and installation quality.

Conclusion

Installing a high-performance exhaust on your 2020 Audi S4 is a tangible way to enhance both driving pleasure and power output. By selecting the right system, preparing thoroughly, and following a meticulous installation procedure, you can avoid common pitfalls and enjoy a drone-free, high-quality upgrade that lasts for many miles. Always consult professional installers if you lack lift access or experienced helpers. With the right approach, your S4 will sound and perform exactly as you intend.