Introduction: Why Upgrade to Perrin Headers on Your WRX?

Installing aftermarket headers on your Subaru WRX is one of the most effective modifications you can make to unlock both performance and a more aggressive exhaust note. Perrin Performance has long been a trusted name in the Subaru community, known for engineering high-quality, direct-fit headers designed specifically for the FA20 and EJ series engines found in WRX and STI models. By replacing the restrictive factory manifold with a set of equal-length or unequal-length Perrin headers, you can experience reduced exhaust backpressure, improved spool, and a noticeable gain in horsepower and torque across the powerband.

This comprehensive guide walks you through the entire installation process step by step, from gathering the right tools to performing the first test drive. Whether you are a seasoned DIYer or a first-time modder, following these instructions carefully will help you complete the job safely and correctly. Always remember that proper installation is critical to avoid exhaust leaks, check-engine lights, or damage to your engine.

Tools and Materials You Will Need

Essential Tools

  • Socket set (metric, 10mm, 12mm, 14mm, 17mm sockets)
  • Torque wrench (capable of reading in ft-lb and in-lb)
  • Ratchet with extensions (3-inch, 6-inch, and a universal joint swivel)
  • Jack and jack stands (or a lift for easier access)
  • Safety goggles and gloves (heat-resistant gloves recommended)
  • Penetrating oil (like WD-40 or PB Blaster)
  • Breaker bar (for stubborn bolts)
  • Wire brush or drill with wire wheel (for cleaning mating surfaces)
  • Perrin header gaskets (usually included with the headers, but order extras)
  • New exhaust manifold studs and nuts (often best to replace when removing old ones)
  • Anti-seize compound (for threads to prevent future seizing)
  • High-temperature RTV silicone (for additional gasket sealing if needed)
  • Exhaust wrap or thermal coating (optional, to reduce under-hood heat)
  • O2 sensor socket (if your WRX has pre-cat oxygen sensors in the factory manifold)

Before starting, verify that your specific WRX model year is compatible with the Perrin headers you have purchased. Perrin offers versions for 2015+ WRX (FA20) and 2008-2014 WRX/STI (EJ257/EJ255). Some kits may require additional modifications like an aftermarket midpipe or a tune.

Safety and Preparation

Working under a vehicle and near hot exhaust components can be dangerous. Follow these preparation steps to set yourself up for success:

  1. Park the WRX on a flat, level surface and engage the parking brake. Chock the rear wheels.
  2. Disconnect the negative battery terminal to prevent accidental electrical shorts or airbag deployment.
  3. Allow the engine to cool completely (at least 2-3 hours if it has been driven). Exhaust components can reach 500°F+.
  4. Jack up the front of the car and securely place jack stands under the front frame rails. Never rely solely on a jack.
  5. Wear safety goggles and heat-resistant gloves throughout the procedure. A long-sleeve shirt is also recommended.

Step 1: Removing the Factory Headers

The factory exhaust manifold on a WRX is a cast-iron piece (on older EJ engines) or a tubular welded manifold (on FA20). It is bolted directly to the cylinder heads and connected to the uppipe (on turbo models) or directly to the catalytic converter. Follow these steps to remove it cleanly:

Clear the Work Area

  • Remove the under-engine plastic splash shield (if equipped) using a 10mm socket.
  • Use penetrating oil on all exhaust manifold nuts and studs. Let it soak for at least 15 minutes.

Disconnect Exhaust Components

On a turbocharged WRX, you will need to unbolt the headers from the uppipe. On naturally aspirated models, disconnect from the catalytic converter or midpipe. Depending on your model, you may also need to remove the front oxygen sensor from the manifold using an O2 sensor socket. Carefully unplug the sensor wiring and set it aside.

Unbolt the Headers

Working from underneath the car, use a 14mm or 17mm socket (depending on bolt size) to remove the nuts securing the manifold to each cylinder head. There are usually four to six bolts per side. A breaker bar or ratchet with a long extension will help reach the rear bolts. If any studs come out with the nut, remove the stud and plan to replace it.

Remove the Manifold

Once all bolts are removed, gently wiggle the factory manifold and pull it out from the bottom of the engine bay. You may need to turn it at an angle to clear the subframe. Repeat for the other side if you have separate left and right manifolds (common on EJ engines).

Clean the Mating Surfaces

Using a wire brush or a drill with a wire wheel, thoroughly clean the cylinder head mounting faces. Remove all old gasket material, carbon buildup, and rust. Any debris left behind will cause an exhaust leak. Wipe the surfaces with a clean rag and brake cleaner for a final clean.

Step 2: Installing the New Perrin Headers

Perrin headers are precision-crafted to fit factory bolt holes and often come with new gaskets. Follow these installation steps carefully:

Prepare the Gaskets and Hardware

Place the new Perrin gaskets onto the cylinder head studs. Ensure the gasket holes align perfectly. If any studs were damaged or missing, install new ones with a dab of anti-seize on the threads. Use a torque wrench to set the studs to the manufacturer’s specification (usually around 15-20 ft-lb).

Position the Headers

Slide the new Perrin headers up into place from the bottom. For most models, you will need to angle the header flange to fit over the studs. Work slowly, and avoid scratching the header finish. Ensure the header collector aligns with the uppipe or downpipe flange.

Bolting the Headers In Place

Hand-tighten all the header nuts first, running them down evenly. Then use a torque wrench to tighten in a crisscross pattern to final torque. For Perrin headers, typical torque is 25-30 ft-lb for the cylinder head nuts and 35-40 ft-lb for the collector flange. Check the instructions provided with your specific kit, as torque values can vary.

Connect the Oxygen Sensors

If your Perrin headers include O2 sensor bungs, reinstall the front O2 sensor and any secondary sensor. Apply a small amount of anti-seize to the sensor threads (do not over-tighten; typically 30 ft-lb). Plug the sensor connectors back in and secure the wiring away from hot surfaces using zip ties.

Step 3: Reassembling and Final Checks

With the new headers installed, reverse the disassembly steps:

  • Reattach the splash shield and any heat shields that were removed (if they clear the new headers).
  • Reconnect the negative battery terminal.
  • Double check all bolts and nuts are tightened to spec under the hood and underneath.
  • Visually inspect that nothing is touching the headers – any contact with wiring, coolant hoses, or the chassis will cause vibration or melting.

Step 4: Testing and Break-In

Before taking your WRX for a road test, perform these checks:

  1. Start the engine and let it idle for 2-3 minutes. Listen for any exhaust leaks – a ticking or hissing sound near the flanges indicates a leak.
  2. If you suspect a leak, use a shop rag over the tailpipe to create backpressure. The hissing will become louder. Tighten the affected bolts or replace the gasket.
  3. Check for any check engine light (CEL) due to the O2 sensor reading change. If the light comes on, you may need an ECU tune (see below).
  4. Go for a short test drive, staying local. Accelerate gently and listen for changes in exhaust note. Monitor coolant temperature and oil pressure gauges.
  5. After the drive, re-torque the header bolts once the engine has cooled. Thermal expansion can cause bolts to loosen slightly after the first heat cycle.

Performance Gains and the Importance of a Tune

Upgrading to Perrin headers will reduce backpressure and allow the engine to expel exhaust gases more efficiently. On a stock WRX, you can expect gains of 10-20 horsepower and 15-25 lb-ft of torque, depending on the specific model and whether you have other modifications. The sound becomes deeper and more aggressive, especially with a cat-back exhaust.

Important: On modern turbocharged WRX models (2015+), installing aftermarket downpipe or exhaust headers often triggers a check engine light due to changed exhaust flow. To realize the full performance benefit and avoid a lean condition, an engine tune (ECU reflash) is highly recommended. Companies like Cobb Tuning or Innovative Tuning offer Accessport tuners and custom maps tailored for header upgrades. Without a tune, you risk running too lean or rich, which can cause engine damage over time.

Heat Management: Wrapping vs. Coating

Aftermarket headers, especially in stainless steel, radiate significant heat into the engine bay. This can raise intake air temperatures and stress nearby components. Two common solutions:

  • Exhaust wrap – A fiberglass-based wrap that insulates the headers. Do this before installation for easier access. Make sure to soak the wrap in water during application and secure with stainless steel ties. Note: wraps can trap moisture and accelerate corrosion on unsupported steel; ceramic coatings are more durable.
  • Ceramic thermal coating – Applied by specialized shops, coating the headers inside and out reduces radiant heat and adds a clean appearance. Many Perrin headers come pre-coated as an option.

If you do neither, ensure your headers have proper clearance from plastic components and hoses. Adding a turbo blanket or heat shield for the uppipe also helps.

Troubleshooting Common Issues

Exhaust Leaks at the Cylinder Head Flange

If you hear a ticking noise after installation, check that the gaskets are centered and that the mating surfaces were clean. Tighten the nuts in the correct sequence. If the leak persists, you may have warped flanges – use a straightedge to check the flange flatness. Perrin headers are generally flat, but imperfections can occur.

Check Engine Light (P0420 Catalyst Efficiency)

On cars with catalytic converters downstream, headers that delete a pre-cat or alter flow can trigger a Catalyst Efficiency code. An O2 spacer (also known as a “mini-cat”) or a proper tune will resolve this. Perrin headers often retain the primary catalytic converter location, but it depends on the specific part.

Difficulty Reaching Bolts

Some of the header bolts, particularly on the driver’s side near the firewall, can be very tight to access. A flexible extension (wobble socket) and a swivel joint are invaluable. Removing the intake box or intercooler (on turbo models) may provide extra room.

Conclusion: Enjoy the Sound and Performance

Installing Perrin WRX headers is a rewarding project that transforms the character of your Subaru. The step-by-step process described above ensures a safe and effective installation, even for beginners. By taking the time to prepare, use the correct torque specs, and address heat management, you can enjoy a louder, more aggressive exhaust note and tangible power gains. If you get stuck, consult the NASIOC forum or Perrin Performance’s technical support for model-specific advice. Always prioritize safety and consider a professional tune to get the most out of your investment.