Introduction: Why Upgrade to a Milltek Sport Cat-Back Exhaust on Your Audi RS5

The Audi RS5 is already a performance-oriented vehicle with a potent V6 or V8 engine (depending on the generation). However, the stock exhaust system is often designed with noise regulations and cost constraints in mind, restricting both sound and flow. Installing a Milltek Sport Cat-Back Exhaust unleashes the engine's true acoustic character while providing measurable performance gains. A cat-back system replaces everything from the catalytic converter back to the tailpipes, using mandrel-bent tubing, high-flow resonators, and precision-engineered mufflers. The result is a deeper, more aggressive exhaust note, reduced backpressure, and a slight bump in horsepower and torque.

This expanded guide walks you through the entire installation process on a B8 or B9 Audi RS5. Whether you are a seasoned DIY mechanic or a first-time installer, following these steps will help you achieve a professional, leak-free fit. We also cover common pitfalls, torque specifications, and post-installation checks to ensure your new exhaust performs flawlessly for years.

Tools and Materials Needed

Having the correct equipment on hand before you begin will save time and prevent frustration. Beyond the Milltek Sport Cat-Back Exhaust kit itself, gather the following:

  • Milltek Sport Cat-Back Exhaust System – Verify you have the correct part number for your specific RS5 year and drivetrain (e.g., B8.5 coupe vs. B9 Sportback).
  • Socket Set with Extensions – Metric sizes (10mm, 13mm, 15mm, 18mm) for OEM bolts and clamps.
  • Wrench Set – Combination wrenches and a ratcheting wrench for tight spaces.
  • Torque Wrench – Critical for tightening clamps to Milltek’s specifications (typically 25–30 ft-lbs for band clamps).
  • Jack and Jack Stands – Use a low-profile floor jack and four quality jack stands. Never work under a vehicle supported only by a jack.
  • Safety Glasses and Gloves – Protect against rust, dirt, and potential pinch points.
  • Penetrating Oil (e.g., WD-40, PB Blaster) – For loosening stubborn exhaust hangers and rusted bolts.
  • Exhaust Hanger Lubricant or Silicone Spray – Makes removing and installing rubber hangers dramatically easier.
  • Rubber Mallet or Dead Blow Hammer – To free stuck hangers without damaging components.
  • Angle Grinder with Cut-off Wheel (optional) – In case a bolt or OEM exhaust section cannot be removed otherwise.
  • Helper – An extra pair of hands for aligning the exhaust tips and supporting the heavy cat-back assembly.

Important: Milltek Sport exhausts are designed for a direct fit. Do not force or modify any pipes. If something does not line up, re-check alignment at the hangers and slip joints.

Preparation Steps

Proper preparation ensures a safe and efficient installation. Follow these steps in order:

  1. Park on a level, solid surface. A concrete garage floor is ideal. Engage the parking brake firmly.
  2. Disconnect the battery. Remove the negative terminal (10mm nut) to prevent any accidental electrical shorts or air suspension issues (if equipped). Let the car sit for 5 minutes before proceeding.
  3. Allow the exhaust to cool completely. If you have driven the car, wait at least one hour to avoid burns.
  4. Lift the vehicle. Using a floor jack at the factory lift points (front subframe for the front, rear diff for the back), raise the car high enough to comfortably work underneath. Place jack stands under the designated pinch weld jacking points. Lower the car onto the stands and test stability by shaking the vehicle.
  5. Clear the work area. Remove any obstacles, tools, or debris that could roll under the car.

Safety note: Never crawl under a vehicle supported only by a hydraulic jack. Always use jack stands rated for the RS5’s weight (approx. 4,000 lbs).

Removing the Stock Exhaust

The removal process requires patience, especially if the car has been driven in winter climates where rust is prevalent. Take your time to avoid breaking studs or damaging the downpipe flanges.

Step 1: Access and Loosen Clamps

Locate the connection between the stock exhaust and the downpipe(s). On an Audi RS5, this is usually a V-band or two-bolt flange near the transmission. Depending on your generation:

  • B8/B8.5 (4.2L V8): Two separate pipes converging near the center.
  • B9 (2.9L V6): Single exhaust path with a Y-pipe later.

Spray penetrating oil on all bolts and flange nuts 10 minutes before attempting removal.

Step 2: Remove Exhaust Hangers

The stock exhaust is suspended by several rubber isolators (hangers). Use a pry bar or a specialized hanger removal tool. Alternatively, apply silicone spray and twist the hangers off with your hands. Work from the rear forward, unhooking each hanger. If a hanger is stuck, use a rubber mallet to tap the exhaust rod out of the bushing.

Step 3: Separate and Lower the Stock Exhaust

With all hangers unhooked and flanges unbolted, the stock exhaust will be free but heavy. Have a helper support the rear section while you maneuver the system out from under the car. On some B9 models, you may need to temporarily drop the rear brace or heat shields for clearance. Lower the exhaust carefully to avoid scratching the bumper or damaging the oxygen sensor wires (if they are attached).

Pro tip: If the exhaust is rusted solid at slip joints, cut the pipe with an angle grinder near the connection. Milltek supplies new pipes, so destroying the old one is acceptable.

Installing the Milltek Sport Cat-Back Exhaust

Now the fun part: fitting your new exhaust. The Milltek system is designed for a bolt-on installation, but careful alignment is key to avoiding rattles and uneven tip gaps.

Step 1: Dry Fit All Sections

Before tightening any clamps, loosely assemble the entire exhaust from the downpipe connection to the tips. Slide the band clamps onto the pipes but do not tighten them yet. This allows you to adjust the positioning.

Step 2: Install Hangers

Attach the new hanger brackets (if included) and slide the rubber isolators onto the exhaust hanger rods. Use silicone spray to ease installation. Ensure each hanger is fully seated and the exhaust is not touching the underbody, heat shields, or driveshaft.

Step 3: Align the Tips

Position the rear sections so that the exhaust tips are centered in the bumper cutouts. The Milltek tips should sit slightly recessed or flush, depending on your preference. Use a measuring tape or a spacer (like a block of wood) to maintain equal gap on left and right sides. Tighten the tip clamps just enough to hold the position.

Step 4: Tighten All Clamps

Work from the front to the rear. Tighten the downpipe flange bolts to the OEM torque specification (usually 30–35 Nm). Then tighten each band clamp progressively, using a torque wrench set to 28 Nm (20 ft-lbs) for Milltek clamps. Do not overtighten, as this can deform the pipe or strip the clamp threads.

Step 5: Final Position Check

With all clamps tightened, recheck tip alignment and hanger tension. If the exhaust sits too low, adjust the rear hangers. If there is contact with the chassis, loosen the relevant clamps, reposition, and retighten.

Important: On B9 RS5 models, ensure the exhaust does not interfere with the rear diff or the active exhaust valves (if keeping them). Milltek provides a version with valve control; if you have a valve-delete system, cap any vacuum lines to prevent check engine lights.

Final Checks and Adjustments

Before lowering the car and celebrating, run through these critical checks:

  • Leak Test: With the engine off, stuff a rag into the tailpipes to create backpressure. Listen and feel for hissing at every joint. Alternatively, use a smoke machine if available. Start the engine and rev gently to hear if there are any obvious leaks.
  • Clearance Inspection: Spin the driveshaft by hand (if accessible) to ensure no contact. Check near the rear sway bar, brake lines, and fuel tank straps.
  • Hanger Security: Jiggle the exhaust from side to side. All rubber isolators should hold firmly without excessive movement.

If you detect a leak, tighten the affected clamp an additional 2–3 ft-lbs until the noise stops. If the leak persists, disassemble the joint, clean the pipe ends, and reassemble with a thin layer of high-temperature exhaust sealant. Milltek recommends dry assembly, but sealant can be used for stubborn leaks.

Post-Installation: Reconnecting Battery and Testing

  1. Reconnect the battery: Reattach the negative terminal and tighten to 10 mm specification.
  2. Start the engine: Listen for abnormal rattles or metallic sounds. The RS5 will idle slightly louder – this is normal. Allow the engine to reach operating temperature.
  3. Check for warning lights: Drive a short distance (1–2 miles) and monitor the dashboard. If a check engine light appears, scan for codes. Common issues include oxygen sensor wiring damage or vacuum leaks from valve control.
  4. Test drive: Take the car on a mix of roads. Accelerate gently and then hard. Listen for drone at highway speeds. Milltek systems are typically free of drone, but individual preferences vary. Note any contact sounds under load or over bumps and adjust hangers accordingly.

Break-in period: The new exhaust will settle over the first 500 miles. The sound may mellow or deepen as carbon deposits form inside the pipes. Re-tighten all clamps after the first heat cycle (let the car cool completely and then re-torque).

Conclusion

Installing a Milltek Sport Cat-Back Exhaust on your Audi RS5 is a highly rewarding modification that amplifies the driving experience. The sound quality, build finish, and performance gains justify the investment. By following this detailed guide – from proper jacking procedures to torque specs – you can complete the installation in a weekend with confidence. Always refer to your specific Milltek kit instructions for any vehicle-to-vehicle variations.

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Enjoy the new soundtrack and the responsive throttle that your Milltek exhaust delivers. Drive responsibly and respect your neighbors – the RS5 is now a true road-going symphony.