Why Upgrade GR86 Headers?

Installing aftermarket headers is one of the most effective modifications you can make to the GR86 (and the related Subaru BRZ and Toyota GR86). The factory headers are heavily restrictive to meet emissions and noise regulations, especially on the FA24 engine found in the second-generation model. Replacing them with a performance set from brands like Perrin or Agency Power unlocks measurable horsepower—typically 15–25 whp—and transforms the exhaust note from a muted, flat drone into a crisp, aggressive sound that complements Subaru’s signature boxer rumble.

Beyond the power gain, headers improve throttle response by reducing backpressure and allowing the engine to breathe more freely. This is particularly noticeable in the mid-range and upper RPM band, where the FA24 truly comes alive. Whether you’re chasing lap times, highway passing power, or simply a more engaging daily drive, headers are a foundational mod that pairs well with a tune, cat-back exhaust, and cold-air intake.

In this expanded guide, we’ll walk through the installation process for both Perrin and Agency Power headers, covering tools, step-by-step removal, specific fitment notes, tuning requirements, and common pitfalls. By the end, you’ll have the confidence to tackle the job yourself or know exactly what to expect from a shop install.

Choosing Between Perrin and Agency Power Headers

Before diving into the install, it’s important to understand the differences between these two popular options. Both are proven performers, but they cater to slightly different priorities.

Perrin Headers

Perrin has a long history with Subaru platforms. Their GR86 header is a stainless steel equal-length design, which balances performance, sound, and durability. The equal-length layout gives a smoother power curve and a more refined exhaust note (less of the uneven cylinder firing “gurgle” some owners love). Perrin includes all necessary hardware, gaskets, and step-by-step instructions. Their header is also CARB-exempt for racing use only, so check your local emissions laws.

Agency Power Headers

Agency Power offers both equal-length and unequal-length header options. For many GR86 enthusiasts, the unequal-length design is the top pick because it emphasizes the classic boxer rumble – that distinctive, offbeat sound that made the BRZ famous. Agency Power headers are typically made from 304 stainless steel, with thick flanges and smooth mandrel bends. They come with new gaskets and bolts, and are also track-use only in terms of emissions compliance.

If you prioritize sound character, Agency Power’s unequal-length design is hard to beat. If you want a clean, broad powerband with a slightly more exotic tone, Perrin’s equal-length setup is an excellent choice.

Tools and Parts List (Expanded)

Having the right tools on hand makes the difference between a smooth afternoon and a frustrating weekend. Here is a complete checklist:

  • Socket set – 10mm, 12mm, 14mm, 17mm, 19mm deep and shallow
  • Torque wrench – 1/2″ drive, settings for ft-lbs (20–80 ft-lb range)
  • Ratchet – 3/8″ and 1/2″
  • Extension bars – 3″, 6″, 12″
  • Flathead and Phillips screwdrivers
  • Combination wrenches – 10mm, 12mm, 14mm, 17mm
  • Header gaskets – usually included; have spare OEM gaskets on hand
  • New bolts / studs – if reusing OEM, clean threads and apply anti-seize
  • Anti-seize compound – copper or nickel based
  • Penetrating oil – for stubborn bolts/nuts (e.g., WD-40 Specialist or PB Blaster)
  • Jack and jack stands – minimum 2-ton capacity
  • Safety glasses and gloves
  • Oxygen sensor socket – 22mm slotted type
  • Shop rags and vacuum cleaner – for debris near open ports

Tip: Some headers require you to reuse OEM studs or springs. Confirm with your kit. Perrin and Agency Power both include gaskets and bolts, but it’s wise to have OEM replacements on hand, especially for the header-to-engine flange.

Preparation: Safety and Access

Proper preparation prevents injury and ensures a clean install.

1. Disconnect the Battery

Disconnect the negative terminal and wait at least 10 minutes to allow the ECU to discharge. This prevents accidental short circuits and also resets fuel trims, which is beneficial when installing a tune later.

2. Lift the Car Safely

Park on a level, hard surface. Loosen the lug nuts slightly, then use a jack to lift the front of the car. Place jack stands under the factory pinch weld points (front and rear on each side). Lower the car onto the stands gently and shake to confirm stability. Remove the wheels for easier access to the header area.

3. Remove Underbody Panels

The GR86 has several plastic underbody covers. Remove them using a 10mm socket or Phillips screwdriver. You’ll need to remove the main belly pan and the small shield near the oil pan. Store the fasteners in a container.

Removing the Stock Headers

This is the most labor-intensive part. Take your time – many bolts are in tight spaces and may be stubborn the first time.

  1. Disconnect the oxygen sensors. Use the O2 sensor socket to unthread both the upstream (front) and downstream (rear) sensors. Mark which sensor goes where – they are not interchangeable. Unplug the wiring connectors from the brackets.
  2. Remove the heat shields. Using a 10mm socket, remove the bolts holding the factory heat shields around the header and the catalytic converter. You may need to cut some zip ties that secure wiring to the shields.
  3. Unbolt the header-to-engine flange. Using a 14mm socket and extension, access the nuts on the studs that connect the header to the cylinder head. There are 6 nuts per side (12 total). Work from the center outward. Apply penetrating oil if needed.
  4. Separate the header from the mid-pipe. Locate the flange where the header meets the front pipe (the “cat pipe”). Unbolt the two 17mm nuts. If the joint is stuck, tap with a rubber mallet.
  5. Remove the header assembly. Gently wiggle the header free from the engine bay. It may require rotating and sliding out through the bottom or from above – the GR86 chassis allows removal from below if you have clearance. Be careful not to damage the studs or oxygen sensor threads.

Note: If you’re installing a header that deletes the primary cat (which both Perrin and Agency Power do), you’ll need a tune or an O2 spacer to prevent a check engine light. We’ll cover that in the tuning section.

Installing Perrin Headers – Step by Step

Now that the stock unit is out, follow these instructions for the Perrin header:

  1. Transfer the oxygen sensors. Remove the sensors from the stock header and install them into the Perrin header. Use anti-seize on the threads (do not get any on the sensor tip). Torque to 20–25 ft-lb.
  2. Prepare the engine flange. Clean the cylinder head mounting surface with a scouring pad or brake cleaner. Place the new gasket onto the studs – ensure the “up” side faces the head (most gaskets have a marking or are symmetric).
  3. Mount the header. Position the Perrin header so the flanges align with the studs. May require slight rotation to clear the oil pan and steering shaft. Slide the header onto the studs, then hand-tighten the 14mm nuts in a star pattern.
  4. Connect the mid-pipe. Slide the two-pipe assembly (or single, depending on version) onto the header outlet. Use the supplied spring bolts or new M10 nuts with lock washers. Do not fully tighten yet.
  5. Torque to spec. Use a torque wrench to tighten the header-to-engine nuts to 27 ft-lb (or as specified in Perrin’s instructions – typically 27–30 ft-lb). Work from the center out. Then tighten the mid-pipe connection to 35 ft-lb.
  6. Reinstall heat shields. Perrin headers often come with a small shield or you can reuse the OEM heat shields if they fit. Secure any wiring that was unclipped.
  7. Reconnect O2 sensors and plug them into the car’s harness.

Installing Agency Power Headers – Step by Step

The Agency Power installation is very similar, with a few key differences:

  1. Check for unequal-length layout. Agency Power’s unequal-length headers have one runner longer than the other. Ensure you route the longer runner away from the engine mount. Dry-fit the header before tightening anything.
  2. Use supplied gaskets. Agency Power includes multi-layer steel gaskets. Apply a thin film of anti-seize to the gasket surfaces if desired, but it’s not needed.
  3. Bolt the header to the head. Same torque: 27–30 ft-lb. Use a star pattern.
  4. Attach the mid-pipe. Agency Power headers typically use a V-band clamp or a flat flange with springs. If using a V-band, ensure the clamp is oriented correctly and tighten to 25–30 ft-lb.
  5. Sensor placement. Some Agency Power headers have a bung on the collector for the wideband O2 sensor. Make sure the sensor does not contact the chassis. If it does, use an O2 spacer or reposition the header slightly.

Pro tip: Both brands recommend checking clearance near the steering shaft and subframe. If the header touches, loosen the bolts and adjust. A slight gap ensures no rattles or heat transfer issues.

Post-Installation Checks and Tuning

1. Verify No Leaks

Start the engine cold and listen for any exhaust hissing. Run your hand (carefully) near the flanges to feel for puffs of air. If you have a smoke machine or can use soapy water, apply it to the gasket joints. Tighten any loose nuts after the first heat cycle.

2. Clear the ECU and Drive

Reconnect the battery. Start the engine and let it idle for 10 minutes. The idle may be rough initially as the ECU adapts. Take a calm 20-minute drive, varying engine speeds. Avoid full throttle until the system learns.

3. Check Engine Light Management

Because both headers remove the primary catalytic converter, you will almost certainly get a P0420 code (catalyst efficiency below threshold) without a tune or O2 spacer. There are three options:

  • Get an ECU tune. Best option – unlocks full power gains and disables the rear O2 sensor. Expect 10–20 more whp after tuning.
  • Install O2 spacers/defoulers. These push the sensor out of the exhaust stream, preventing the code. Works for many but not 100% reliable.
  • Use a piggyback like the OFT or Ecutek. Provides a base map pre-configured for headers.

4. Sound and Performance Expectations

Both headers will significantly increase volume at wide open throttle. Expect a deeper tone with more crackles on deceleration. With an equal-length header (Perrin), the sound is smoother and higher-pitched; with unequal-length (Agency Power), you get the classic boxer rumble. Power gains will be most noticeable above 4000 RPM.

Common Pitfalls and How to Avoid Them

  • Stripped studs. The factory studs can seize. If a nut spins but won’t come off, use a nut splitter or cut it off. Replace the stud with a new one from Subaru (part 800610860).
  • O2 sensor wire routing. Route the sensor wiring away from the headers. Use heat wrap or zip ties to keep it off the tubes.
  • Steering shaft interference. After installation, turn the steering lock-to-lock. If the header contacts the shaft, you may need to dimple the header tube (carefully) or add a small clearance bend. This is rare but has happened with wide-tube designs.
  • Leaks after heat cycling. Re-torque the header bolts after the first 100 miles. The gaskets settle and require a second pass.

Long-Term Maintenance and Considerations

Stainless steel headers will develop a blue/gold patina over time – this is normal. High heat can discolor but does not affect performance. If you live in a region with road salt, consider ceramic coating to prevent corrosion and reduce underhood temperatures.

Headers also increase underhood heat, which can affect intake temperatures. Upgrade your intercooler or intake to a heat-shielded design if you track the car. Additionally, header wrap can be added, but be aware it may trap moisture and accelerate corrosion on non-coated stainless pipes.

Final Thoughts

Installing headers on your GR86 is a rewarding project that transforms the driving experience. Whether you choose Perrin’s equal-length design for a refined powerband or Agency Power’s unequal-length headers for that iconic boxer sound, the process is straightforward with the right tools and patience. Follow the torque specs, re-torque after heat cycling, and pair the upgrade with a proper tune to maximize results. Your GR86 will reward you with stronger acceleration, improved throttle response, and a soundtrack that turns heads.

For further reading, check out Perrin Performance’s official install guide and Agency Power’s product page. For tuning options, visit OpenFlash Tablet or consult a local dyno shop. Happy wrenching!