The Audi B9 S4 is already a formidable machine, but even the best stock exhaust leaves performance on the table. If you are looking to unlock a deeper, more aggressive exhaust note while picking up a few extra horsepower, the AWE Tuning Exhaust system is one of the most popular and proven upgrades. Priced around $1,200, this system delivers a transformative driving experience. This expanded guide covers everything from why this exhaust is a worthy investment to detailed installation tips, common pitfalls, and complementary modifications.

Why the AWE Tuning Exhaust Stands Out

AWE Tuning has built a reputation for precision engineering and exhaust systems that prioritize sound quality without drone. For the B9 S4, they offer several configurations to suit different tastes. Here’s what makes the AWE system a top choice:

  • Material and construction: Made from T304L stainless steel with CNC-mandrel bent tubing, the system resists corrosion and cracking. The wall thickness and welds are done by hand to ensure durability.
  • Sound profiles: AWE provides both a Resonated and Non-Resonated option. The Resonated version smooths out high-frequency rasp for a more mature tone, while the Non-Resonated is louder and more aggressive. Both eliminate the factory’s overly muffled volume.
  • Drone mitigation: Unlike many aftermarket systems, AWE’s 180 Technology® uses a helmholtz resonator to cancel out drone frequencies at cruising speeds. This means you get a thrilling sound under throttle but a quiet cabin on the highway.
  • Weight savings: The full cat-back system sheds about 30 pounds compared to the stock exhaust. Less weight on the rear axle can improve handling and throttle response.
  • Performance gains: On a dyno, the AWE exhaust alone adds roughly 5–8 horsepower and 10–15 lb-ft of torque at the wheels. When paired with a tune and downpipes, those numbers climb significantly.

Before buying, decide between the Resonated or Non-Resonated version. Many owners start with Non-Resonated and later add the optional resonated mid-pipes if they want less volume. Both options are compatible with the factory quad-tip look.

What to Expect: Sound and Performance Gains

Sound Character

The stock B9 S4 exhaust is surprisingly quiet, muted by restrictive mufflers and particulate filters. After installing the AWE system, the first thing you will notice is a rich, European-sounding baritone at idle and a bellowing roar above 3,500 RPM. Cold starts gain a brief, satisfying growl. Under hard acceleration, the Non-Resonated version can produce a sharp crackle on upshifts. The Resonated version retains a full, deep tone without the raspiness that sometimes comes with opened-up turbo engines.

Performance Data

Independent testing shows peak gains of +7 hp and +12 lb-ft at the wheels. More importantly, the power curve feels stronger in the mid-range, helping the car pull harder between shifts. Combined with a stage 1 ECU tune, the AWE exhaust can unlock another 10–15 wheel horsepower. The increased airflow also helps keep exhaust gas temperatures lower during track use.

If you plan to add a downpipe later, the AWE system is designed to pair directly with aftermarket downpipes without modifications. Many enthusiasts combine it with a Unitronic or 034Motorsport stage 2 tune for a complete package.

Tools and Preparation

Having the right tools and a clean workspace makes the installation smoother. Here’s the full list:

  • Socket set (metric: 10mm, 13mm, 15mm, 18mm sockets)
  • Combination wrenches (13mm, 15mm, 18mm)
  • Torque wrench (range 20–100 ft-lb)
  • Breaker bar for stubborn bolts
  • Penetrating oil (e.g., PB Blaster or Kroil)
  • Jack and two jack stands (minimum 3-ton capacity)
  • Rubber mallet (to loosen hangers)
  • Flathead screwdriver (for hose removal)
  • Safety glasses and mechanic’s gloves
  • Optional: exhaust hanger tool, quick jack system
  • New exhaust gaskets (if not included with the kit – check first)

Park on a level surface and allow the engine and exhaust to cool completely. A hot exhaust can cause burns and makes bolts harder to torque. Apply penetrating oil to all exhaust flange bolts 30 minutes before starting. For rust-prone vehicles, consider replacing the downpipe-to-cat-back hardware with stainless steel bolts.

Step-by-Step Installation Guide

1. Prepare and Lift the Vehicle

Use the jack to raise the rear of the car to a comfortable working height. Place jack stands under the designated lift points on the frame rails. Verify the vehicle is stable before crawling underneath. Remove any under-tray panels that block access to the exhaust hangers. On some B9 S4s, a heat shield may need to be loosened. Keep these fasteners safe.

2. Remove the Stock Exhaust

Start at the rear. Loosen the bolts connecting the exhaust to the downpipes (two bolts at each flange, usually 13mm or 15mm). They are tight—use the breaker bar. Next, disconnect the rubber hangers by pulling/pushing the hanger brackets. A little soapy water or silicone spray on the rubber makes them slide off easier. Carefully lower the rear muffler section, then the mid-pipes. The factory exhaust is heavy, so have a helper or a transmission jack. Remove the entire cat-back system from the vehicle. Keep the factory hanger brackets and rubber mounts—you will reuse them.

3. Install the AWE Exhaust

Begin with the mid-pipe section. Attach it to the downpipe flanges using the provided hardware. Do not fully tighten yet—leave the bolts finger-tight to allow adjustments. Slide the rubber hangers onto the AWE hanger rods (apply lubricant). Next, hang the rear muffler section. Align the pipes carefully to avoid contact with the underbody, driveshaft, or heat shields. The AWE system is jig-welded for a precise fit, but slight tweaks may be needed. Ensure the exhaust tips are centered in the bumper cutouts.

4. Tighten and Final Check

Once everything is in place, tighten the flange bolts to the manufacturer’s torque spec: 30–35 ft-lb for the downpipe connection and 15–20 ft-lb for the inter-module clamps. AWE provides a torque chart in the box. Re-tighten all hanger connections. Double-check clearance around the rear differential and sway bar. Spin the tips to verify they are parallel and level. Reattach any heat shields removed earlier.

5. Lower and Test

Remove the jack stands and lower the car. Start the engine and listen for any hissing or rattling. Let the engine reach operating temperature. Inspect all flanges for leaks with a gloved hand—if you feel exhaust gas, tighten a bit more. Take a short test drive at varying RPMs to ensure no drone or strange vibrations. Many owners find the sound breaks in after about 100 miles as carbon builds up on the packing.

Common Pitfalls and How to Avoid Them

  • Leaks at flange connections: Always use new gaskets (AWE supplies them). Clean the downpipe surface with a wire brush before assembly. Over-tightening can crush the gasket, so use a torque wrench.
  • Hanger rattles: If you hear a metallic rattle, one of the hanger rods may be touching the car’s body. Use a rubber mallet to gently adjust the rod angle. Alternatively, install rubber isolators from the factory positions.
  • Tip alignment: The quad tips must be aligned symmetrically. Loosen the rear clamps, adjust the tips, then re-tighten to 15 ft-lb. A small mirror helps verify alignment.
  • Heat shield interference: On some models, the heat shield near the driveshaft may contact the new mid-pipes. Spacers (washers) can be used to push the shield away.
  • Check engine light (CEL): The cat-back alone will not throw a CEL. But if you pair it with a downpipe, your car may need a tune or O2 sensor spacer to avoid a catalyst efficiency code.

Alternatives and Complementary Upgrades

Downpipes

Installing high-flow or catless downpipes with the AWE exhaust dramatically increases volume and power. Expect a gain of 25–40 whp with a proper tune. Brands like 034Motorsport and Red Star offer direct-fit downpipes that bolt to the AWE system.

Intercooler and Intake

To really take advantage of the exhaust flow, upgrade the intercooler to reduce intake air temperatures. The GM-style stepped intercooler from Wagner Tuning is a popular choice. A larger cold air intake (e.g., from Integrated Engineering) complements the exhaust sound and adds a few more horsepower.

ECU Tune

A stage 1 tune from Unitronic, APR, or 034Motorsport will increase boost and timing, making the exhaust worth 10–15 whp extra. The combination of exhaust and tune transforms the S4 into a true mid-tier sports car rival.

Cost Breakdown and Value

The AWE Tuning exhaust system retails for approximately $1,199–$1,299 depending on the configuration (Resonated or Non-Resonated) and any special finishes (black chrome tips add $100). Installation at a reputable shop runs $200–$400 for labor. DIY installation saves that cost. Total investment: around $1,200–$1,700. Compared to other European performance upgrades, this is very competitive. The system is backed by AWE’s limited lifetime warranty, and the improvement in driving engagement is immediate.

If you plan to keep your S4 for several years, this modification holds value well on the used market. Many owners easily resell the system for 60–70% of the original price when they upgrade to a new car.

Conclusion

Installing an AWE Tuning Exhaust on your B9 S4 is one of the most satisfying modifications you can make. The combination of weight savings, a richer exhaust note, and modest power gains transforms an already capable daily driver into a thrilling weekend toy. With careful preparation and attention to detail, the installation is straightforward even for intermediate DIYers. Whether you choose the refined Resonated version or the rowdy Non-Resonated setup, you will notice the difference every time you start the engine. Enjoy the roar—you’ve earned it.