Why Upgrade to the ERL Performance Cat-Back Exhaust?

The ERL Performance Cat-Back Exhaust system is engineered specifically for the Mercedes-AMG M177 engine, which powers vehicles like the C63 S, E63 S, GLC63, and GT 4-Door. Unlike generic aftermarket systems, the ERL cat-back is designed to optimize exhaust flow while preserving the factory’s precise variable valve timing and turbo spool characteristics. The result is a noticeable gain in peak horsepower—typically 15–25 wheel horsepower with no other modifications—combined with a deep, aggressive exhaust note that eliminates the stock system’s muffled tone without introducing unwanted drone at cruising speeds. This guide provides a detailed, shop-quality walkthrough for installing the ERL cat-back exhaust on any M177-equipped vehicle, covering every step from prep to final leak check.

Tools and Materials Needed

Essential Tools

Before you begin, assemble the following tools. Having everything at hand minimizes downtime and prevents frustrating trips to the toolbox during the install.

  • Floor jack and two heavy-duty jack stands – minimum 3-ton capacity to safely lift the vehicle’s rear
  • 3/8-inch and 1/2-inch drive socket sets – metric sockets from 10mm to 18mm, including deep sockets for hanger bolts
  • Ratchet and breaker bar – a 24-inch breaker bar helps break loose rusted factory fasteners
  • Torque wrench – a 1/2-inch drive torque wrench capable of 30–80 ft-lb for final tightening
  • WD-40 or penetrating oil – liberal application on bolts 30 minutes prior to removal reduces breakage risk
  • Rubber mallet – to gently tap stubborn exhaust hangers out of isolators
  • Safety glasses, mechanic’s gloves, and ear protection
  • Cutting tool (optional) – an oscillating multi-tool with a metal blade or a reciprocating saw may be needed if the factory exhaust has been welded at any point

Materials from the Kit

Inside the ERL Performance Cat-Back Exhaust box, verify you have all components before starting. The kit typically includes:

  • Front and rear exhaust sections with integrated resonators
  • Bypass valve connection pipes (if equipped with the factory active exhaust system)
  • Stainless steel hardware: clamp bolts, spring bolts, and spacers
  • New rubber isolators (often pre-installed on hangers)
  • Gaskets for the catalytic converter connection

If any parts are missing, contact ERL Performance directly or your authorized dealer before beginning the install. Do not attempt to reuse rusted factory gaskets—they will almost certainly leak.

Preparation and Safety

Park the vehicle on a level concrete surface. Allow the engine and exhaust system to cool completely—ideally overnight. A cold system is safer to work around and prevents burns from catalytic converters, which can remain hot for hours after driving. Engage the parking brake and chock the front wheels. Disconnect the negative battery terminal to avoid accidental short circuits when working near the exhaust valve actuator wiring.

Raise the rear of the vehicle using the floor jack at the factory-recommended lift point (the rear subframe or differential housing). Place jack stands under the rear axle jack points on both sides. Lower the vehicle gently onto the stands and test stability by pushing at the rear bumper. Never rely solely on the floor jack.

Step 1: Remove the Stock Cat-Back Exhaust

1A. Locate and Loosen All Connection Points

Slide under the vehicle and identify the factory exhaust path. The cat-back section begins immediately after the downstream oxygen sensor bungs on the catalytic converters. There are four main connection points:

  • Cat flange connections – two flanges (one per bank) where the stock exhaust bolts to the downpipes/catalytic converters. These are typically secured with two M10 or M12 bolts each.
  • Hanger isolators – usually three to four rubber hangers that attach the exhaust to hooks on the chassis. They are located near the center muffler and the rear axle.
  • Rear muffler bracket bolts – two bolts that secure the muffler to a support brace near the rear bumper.
  • Exhaust valve actuators (if applicable) – vehicles with the factory active exhaust have actuators on the rear muffler; unplug the electrical connectors before removal.

Spray penetrating oil onto every bolt and hanger stud you can reach. Wait 10–15 minutes for it to penetrate.

1B. Remove the Bolts and Hangers

Use a socket and breaker bar to loosen the cat flange bolts. If they are stubborn, apply additional penetrating oil and let it soak longer. Do not apply excessive force that could snap the studs—if a bolt is severely rusted, consider using a bolt extractor or cutting it with a reciprocating saw.

Once the flange bolts are removed, work on the rubber hangers. Use a flathead screwdriver to pry the rubber isolator off the chassis hook while pulling the exhaust away. A rubber mallet tapped on the hanger loop can help free it. For the rear muffler bracket, remove the two bolts with a socket.

1C. Lower the Stock Exhaust

After all connections are freed, slide the stock exhaust sections carefully from under the vehicle. The system is heavy—using a helper or a transmission jack prevents injury. If the exhaust is in sections, extract each piece separately. Set the old system aside or recycle it.

Step 2: Prepare the ERL Exhaust Components

Lay out the ERL cat-back sections on a clean surface. Inspect each pipe for any dents, scratches, or missing hardware. Check that the included gaskets match the factory flange pattern. If your M177 vehicle has active exhaust valves, confirm that the ERL system’s valve actuator brackets align with your factory wiring harness.

Slide the provided rubber isolators onto the hanger rods of the ERL exhaust if not pre-installed. A small amount of soapy water on the isolator bore makes installation easier. Dry fit the two main sections together without tightening—ensure the flange holes align and the system sits straight.

Step 3: Install the ERL Cat-Back Exhaust

3A. Attach to the Catalytic Converters

Lift the front section of the ERL exhaust into position. Align the flanges with the factory catalytic converter flanges. Insert the new gaskets between the flanges (note orientation—some gaskets have a direction). Hand-thread the bolts, then tighten them using a socket and ratchet. Do not final torque yet—you want slight adjustability for alignment.

3B. Connect the Center and Rear Sections

Slide the rear muffler section of the ERL system into the front section’s slip joint or clamp connection (depending on kit design). Loosely tighten the clamp. Hang each hanger rod into its corresponding chassis hook—work from front to rear. Use the rubber mallet to fully seat the isolators. Reinstall the rear muffler bracket bolts but leave them slightly loose.

3C. Align the System

With all connections loosely assembled, check the exhaust tip alignment at the rear bumper. The tips should be centered in the cutouts and level left-to-right. Adjust the hanger positions and the slip joint/clamp to achieve perfect symmetry. This step is critical for a professional appearance and to prevent contact with the underbody that could cause rattles.

Step 4: Torque All Connections to Specification

Once alignment is satisfactory, begin final tightening. Use a torque wrench for all critical fasteners:

  • Cat flange bolts: 40–45 ft-lb (check ERL specifications; factory spec is typically 40 ft-lb)
  • Slip joint or band clamp: 30–35 ft-lb
  • Rear muffler bracket bolts: 30 ft-lb
  • Hanger isolator hooks: hand-tight only; do not over-torque the threaded hooks provided with some kits

Double-check that all bolts are evenly tightened and that no gasket is pinched. If your vehicle has active exhaust valves, reconnect the actuator electrical connectors now. Ensure the wiring is routed away from hot pipes and moving suspension components.

Step 5: Check for Leaks

Start the engine and allow it to idle. The ERL system will be louder than stock even at idle—this is normal. Walk around the vehicle and listen for any hissing sounds that indicate a leak at the flanges or clamps. You can also use a piece of tissue paper or a soapy water spray (do not use soapy water on hot exhaust – wait until the pipes are cool again or use a handheld “exhaust leak detector” tool). If you hear a leak, tighten the affected bolts slightly further (within torque range) or adjust the gasket.

Rev the engine gently to 2000–3000 RPM and check for exhaust pulses escaping from connections. Pay close attention to the cat flanges and the slip joint. Also inspect the O2 sensor bungs if the ERL system includes a secondary bung location (some M177 cats have a downstream bung; ensure it is capped or plugged if not used).

Step 6: Lower the Vehicle and Perform a Road Test

Turn off the engine, allow it to cool for a few minutes, and then lower the vehicle from the jack stands. Remove the wheel chocks. Do a thorough visual inspection underneath—ensure that the exhaust clears the rear axle, control arms, and body braces. There should be at least 1 inch of clearance around all moving parts to prevent contact during suspension travel.

Take the vehicle on a 10–15 minute test drive that includes city streets (for low-speed rattles) and a short stretch of highway (to evaluate drone and resonance). With the ERL cat-back, you should notice a deeper tone on acceleration with minimal interior drone at cruising speeds. If you detect a metallic rattle, it is often caused by the exhaust contacting a heat shield or chassis brace—re-center the system slightly and retighten.

After the test drive, let the system cool and re-check all external bolt torques. The heating and cooling cycle may cause clamps to loosen slightly. A second torque verification after 100–200 miles is recommended by ERL.

Post-Installation Tips and Break-In

Like many aftermarket exhausts, the ERL cat-back may sound a bit “tinny” or metallic for the first 50 miles. This is normal as the stainless steel and internal packing settle. The tone will deepen and smooth out over 200–300 miles of driving. Avoid extended full-throttle runs during the first 100 miles to let the gaskets and seals fully seat.

If your M177 is equipped with the factory active exhaust (button-controlled valves), the ERL system’s valves will mate directly to the factory actuators. No coding or modifications are needed. However, some users prefer to install a valved exhaust controller (like a remote module) to force the valves open or closed independently. This is an optional aftermarket upgrade and is not required for the ERL cat-back function.

Common Issues and Troubleshooting

1. Leak at Cat Flange

Cause: Gasket misaligned or reused factory gasket. Fix: Use only the new gaskets from the ERL kit. Ensure the gasket is centered on the flange before tightening bolts in a cross pattern.

2. Exhaust Hanger Rattle

Cause: Rubber isolator not seated fully, or a metal-on-metal contact at the hanger hook. Fix: Apply silicone spray to the isolator and push it all the way onto the chassis hook. If the hanger rod itself touches a heat shield, bend the heat shield slightly away with pliers.

3. Muffler Flange Leak

Cause: The slip joint clamp not tightened evenly. Fix: Loosen the clamp, apply exhaust sealant (high-temp) to the pipe overlap, and re-torque to 35 ft-lb.

4. Valve Actuator Error (CEL or Dash Warning)

Cause: Actuator electrical connector not fully seated, or wiring pinched during installation. Fix: Check connector for corrosion and click. If the warning persists, clear the OBD-II code with a scan tool after verifying no wiring damage.

Conclusion

Installing the ERL Performance Cat-Back Exhaust on your M177-powered Mercedes-AMG is a straightforward weekend project that dramatically improves the car’s exhaust note and frees up engine breathing. With careful attention to alignment, torque specifications, and leak checking, you can achieve a factory-quality fit that will last for years. The combination of sharper throttle response, a deeper growl, and modest power gains makes this one of the most satisfying upgrades for the M177 platform.

For further reading, we recommend checking out the official ERL Performance website for product details and warranty information. The MBWorld C63/S forum has numerous owner-install threads with photos that can help if you encounter unusual fitment. A video install by European Auto Source covers the process live on an E63 S. For torque specifications on M177 exhaust hardware, consult the Mercedes WIS/ASRA or a specialty service manual resource.