Upgrading your Subaru WRX with an aftermarket axle-back exhaust system is a popular modification that not only amplifies the car's aggressive exhaust note but can also improve exhaust flow, potentially enhancing throttle response and overall performance. While the installation process is straightforward for those with basic mechanical skills, it requires attention to detail and the right tools to ensure safety and optimal results. This comprehensive guide provides step-by-step instructions, helpful tips, and expert advice to help you successfully install your new axle-back exhaust system.

Understanding Axle-back Exhaust Systems

An axle-back exhaust system replaces the portion of the exhaust from the rear axle to the exhaust tips, including the muffler and tailpipes. Unlike cat-back systems, axle-back upgrades primarily affect the sound and aesthetics of your Subaru WRX without major modifications to the catalytic converters or mid-pipe sections. This makes axle-back systems a popular choice for enthusiasts seeking a deeper, more aggressive exhaust tone while maintaining emissions compliance and factory-like drivability.

Before beginning installation, it's important to confirm that the axle-back exhaust you purchased is specifically designed for your Subaru WRX's model year and trim, as fitment can vary. Additionally, some aftermarket systems may require minor adjustments or additional hardware for a perfect fit.

Preparation Before Installation

Gather Necessary Tools and Materials

Having all your tools and parts ready before you start will streamline the installation process. You should prepare the following:

  • Floor jack and sturdy jack stands or ramps
  • Socket set (commonly 10mm, 12mm, 14mm sockets)
  • Ratchet wrench and extensions
  • Penetrating oil such as WD-40 or PB Blaster
  • Torque wrench (recommended for proper tightening)
  • Rubber mallet (optional, for gentle adjustments)
  • Safety glasses and gloves
  • Anti-seize compound (optional, for bolts)
  • Shop rags or paper towels

Vehicle Safety and Positioning

Park your Subaru WRX on a level surface and engage the parking brake. For maximum safety, disconnect the negative terminal of your vehicle's battery to prevent any accidental electrical shorts or shocks during the process. Using a floor jack, carefully lift the rear of the car and place it securely on jack stands. Alternatively, you can use ramps designed for vehicle maintenance. Never work under a vehicle supported only by a jack.

Inspect the Exhaust System

Before removal, inspect the stock exhaust system for signs of rust, corrosion, or damage. This will help you anticipate any difficulties during removal and assess if additional parts such as replacement gaskets or hardware may be necessary.

Removing the Stock Axle-back Exhaust

Locate and Access Mounting Points

The stock axle-back exhaust is secured to the mid-pipe by clamps or bolts and hung from rubber exhaust hangers attached to the chassis. Locate these mounting points and assess their condition. Applying penetrating oil to all nuts, bolts, and clamps is critical to loosen rusted or stuck hardware and prevent breakage.

Detach Exhaust Hangers

Using pliers or a pry tool, carefully remove the exhaust hangers. These rubber mounts can be stubborn, especially on older vehicles, so take your time to avoid tearing them or damaging the chassis mounts. If the hangers are worn or damaged, consider replacing them during reinstallation to ensure proper fitment and vibration isolation.

Loosen Clamps and Bolts

Using your socket set, begin loosening the clamps or bolts connecting the axle-back exhaust to the mid-pipe. It is best to fully remove these fasteners once loosened. Keep all hardware if you plan to reuse it, or dispose of it if your new exhaust kit comes with replacement parts.

Remove the Stock Exhaust

Once all fasteners and hangers are detached, gently wiggle and pull the axle-back exhaust away from the mid-pipe. Be cautious not to damage surrounding components such as brake lines, suspension parts, or wiring harnesses. If the exhaust is stuck, applying additional penetrating oil and gently tapping with a rubber mallet can help loosen it. Avoid using excessive force as this can cause damage.

Inspect and Clean Connection Points

With the stock axle-back removed, thoroughly inspect the mid-pipe flange or slip joint for rust, carbon buildup, or damage. Use a wire brush or sandpaper to clean the mating surfaces to ensure a proper seal with the new exhaust. Also, check the condition of the exhaust hangers and replace if necessary.

Installing the Aftermarket Axle-back Exhaust

Pre-assembly and Fitment Check

Before final installation, loosely assemble the new axle-back exhaust components on the ground to familiarize yourself with the fit and orientation. This step helps identify potential fitment issues and prepares you for the actual installation under the vehicle.

Attach Exhaust to Mid-pipe

Position the new axle-back exhaust onto the mid-pipe connection. If your exhaust uses a slip-fit design, ensure the slip joint is clean and apply a thin coat of anti-seize compound to help with future removal. Slide the exhaust over the mid-pipe, aligning it properly to avoid leaks.

Secure Clamps and Hardware

Install the clamps or bolts provided with your exhaust kit at the mid-pipe connection, hand-tightening them at first to allow for adjustments. Verify the new exhaust’s alignment relative to the vehicle’s rear bumper and wheel wells. The exhaust tips should be centered in the cutouts or visible areas, neither too far inside nor protruding excessively.

Attach Exhaust Hangers

Carefully mount the new exhaust onto the rubber hangers. If the hangers are tight or difficult to install, using a small amount of lubricant like soapy water can ease the process. Confirm that the exhaust is properly supported and not putting undue stress on any hangers or chassis mounts.

Torque All Fasteners

Once the exhaust is positioned correctly, use a torque wrench to tighten all clamps and bolts to the manufacturer’s recommended specifications. Proper torque prevents leaks and ensures the exhaust stays securely in place during driving. Over-tightening can damage components, so adhere strictly to torque values.

Post-Installation Checks and Testing

Lower the Vehicle Safely

After securing the exhaust, carefully remove the jack stands and lower your Subaru WRX to the ground. Reconnect the negative battery terminal to restore electrical systems.

Initial Engine Start and Leak Inspection

Start the engine and listen closely for any exhaust leaks, rattles, or unusual noises. A slight ticking or hissing sound near joints may indicate a leak that needs tightening or repositioning. You can also use a soapy water spray around joints to check for escaping exhaust gases—bubbles will form where leaks exist.

Visual Inspection of Exhaust Alignment

With the engine running, visually inspect that the exhaust tips remain centered and clear of the bumper and body panels to avoid heat damage or rattling. Adjust if necessary.

Test Drive and Final Verification

Take your WRX for a short drive, paying attention to exhaust sound, vibrations, and any abnormal behavior. The sound should be deeper and more aggressive without unwanted drone or resonance inside the cabin. After the drive, recheck all fasteners to ensure they remain tight.

Additional Tips for a Successful Installation

  • Work in a well-ventilated area: Exhaust fumes are hazardous; avoid enclosed spaces when testing your exhaust.
  • Use quality replacement hardware: If your stock bolts or clamps are heavily corroded, replace them with stainless steel hardware to prevent future issues.
  • Consider professional alignment: Some aftermarket exhausts benefit from minor adjustments or welding; consult a professional if unsure.
  • Wear protective gear: Safety glasses and gloves protect you from debris, sharp edges, and chemicals.
  • Keep a fire extinguisher nearby: When working with penetrating oils and tools near hot components, safety first.
  • Apply anti-seize compound: Using anti-seize on bolts and clamps facilitates easier removal during future maintenance or upgrades.
  • Check local regulations: Ensure your aftermarket exhaust complies with noise and emissions standards in your area to avoid fines or failed inspections.

Maintaining Your Aftermarket Axle-back Exhaust

To prolong the life and appearance of your new exhaust system, periodic maintenance is recommended. Regularly inspect the exhaust for loose hardware, rust spots, and damage from road debris. Cleaning the exhaust tips with metal polish enhances their shine and prevents corrosion. Additionally, addressing rattles or vibrations early can prevent more serious issues.

If you encounter any persistent exhaust leaks or unusual noises, it’s advisable to have a professional mechanic perform a detailed inspection to ensure there are no hidden problems.

Conclusion

Installing an aftermarket axle-back exhaust on your Subaru WRX is a rewarding upgrade that can significantly enhance your vehicle’s auditory appeal and, to some extent, its performance. By following these detailed installation steps and safety precautions, you can confidently complete the job yourself while ensuring a precise fit and reliable operation. Remember, patience and careful attention to detail are key to a successful installation. Enjoy the enhanced sound and style your new exhaust brings to your WRX!