Introduction: Why Upgrade to GReddy Headers on Your BRZ

Installing aftermarket headers is one of the most effective modifications you can make to unlock the true potential of your Subaru BRZ or Toyota 86. The factory exhaust manifold on these cars is notoriously restrictive, with a heavy cast-iron design that hampers exhaust gas flow and robs the engine of power, especially in the mid-to-high rpm range. GReddy headers, known for their precise engineering and high-quality T304 stainless steel construction, offer a significant upgrade by reducing back pressure and improving scavenging. This can yield gains of 10–15 horsepower and a similar increase in torque, along with a more aggressive exhaust note.

However, installing headers is not a plug-and-play job. It requires mechanical skill, the right tools, and attention to detail. This guide will walk you through every step, from preparation to final testing, ensuring a safe and successful installation. We'll also cover critical post-installation considerations such as ECU tuning, because running aftermarket headers without a proper tune can lead to check engine lights and suboptimal performance. Let's get started.

Tools and Materials You'll Need

Before lifting the car, gather all necessary tools and parts. Having everything on hand will prevent frustrating delays.

Tools

  • Socket set with metric sockets (10mm, 12mm, 14mm, 17mm, 19mm, 22mm)
  • Torque wrench (capable of measuring 20–50 ft-lb range)
  • Breaker bar (for stubborn bolts)
  • Ratchet and extensions (6-inch and 12-inch)
  • Jack and two jack stands (rated for the vehicle weight)
  • Penetrating oil (like PB Blaster or Kroil)
  • Wire brush (for cleaning studs and flanges)
  • Heat-resistant gloves and safety glasses
  • Shop rags or paper towels

Parts and Consumables

  • GReddy headers (specific model for FA20 engine)
  • New header gaskets (OEM or high-quality aftermarket, such as Grimmspeed or Cusco)
  • New exhaust manifold studs and nuts if old ones are corroded (optional but recommended)
  • Anti-seize compound (for threads)
  • Medium-strength thread locker (blue Loctite) for header-to-cat-pipe bolts
  • New O2 sensor gaskets (if reusing stock sensors)
  • Copper-based assembly lube for gasket surfaces (optional)

Note: Some aftermarket headers require a flex joint or V-band clamp adapter if they use a different connection than OEM. Check the GReddy kit documentation.

Preparation and Safety

Proper preparation ensures a smooth installation and avoids common pitfalls. Park the car on a level surface, engage the parking brake, and disconnect the negative battery terminal. This prevents accidental short circuits or electrical damage while working near sensors.

Raising the Vehicle

Using a floor jack, lift the front of the car at the factory jacking point (the front crossmember or subframe). Place jack stands under the reinforced pinch weld points behind the front wheels. Lower the car onto the stands and shake it gently to confirm it is stable. Never work under a car supported only by a jack. For additional clearance, you may also jack up the rear slightly to allow the exhaust system to hang more freely.

Protect Yourself

Exhaust components get very hot. Work on a cold engine only – ideally after the car has sat overnight. Wear heat-resistant gloves to avoid burns from hot studs, and safety glasses to protect from falling debris or penetrating oil splatter.

Removing the Stock Headers

Removing the factory manifold is the most challenging part of the job, often complicated by rust and limited access. Spend extra time on preparation to avoid broken studs.

Step 1: Apply Penetrating Oil

Spray penetrating oil generously onto all exhaust manifold studs and the bolts connecting the header to the cat pipe. Let it soak for at least 10–15 minutes, preferably longer if bolts are rusty. This significantly reduces the risk of snapping studs.

Step 2: Remove Undertray and Heat Shields

Remove the plastic under-engine splash shield (if equipped) using a 10mm socket or screwdriver. This gives you access to the bottom of the headers. Next, remove any OEM heat shields that are bolted to the manifold. They are often held by 10mm or 12mm bolts. Set them aside; some can be reused, but many aftermarket headers do not use them.

Step 3: Disconnect the Downpipe/Cat Pipe

Working from underneath, locate the connection between the stock header collector and the front portion of the exhaust (the overpipe or cat pipe). The bolts are typically two 14mm or 17mm nuts. If they are stubborn, use the breaker bar. Remove the nuts completely, then separate the flanges. You may need to pry gently with a flathead screwdriver. The entire exhaust will now be unsupported from the header side.

Step 4: Unbolt the Headers from the Engine

Access the header studs from above and below. The stock manifold is held by eight or nine studs (three per cylinder head, plus one in the center). Use a 12mm or 14mm deep socket with a ratchet and extension. Work slowly, applying penetrating oil again if any bolt feels tight. Remove all nuts and extract the manifold. You may need to wiggle it out from under the car – it is heavy and awkward. Be careful not to damage the wiring harness or O2 sensor wires.

Step 5: Remove O2 Sensors (if necessary)

If the GReddy headers have different O2 sensor bungs, you'll need to swap the sensors. Use a specialized O2 sensor socket or a 22mm wrench. Apply anti-seize to the threads before reinstalling into the new bungs. If the sensors are stubborn, heat them with a propane torch – the thermal expansion helps break the bond.

Tips for Stubborn Bolts

  • Use a breaker bar with a six-point socket for maximum grip and less chance of rounding.
  • If a stud snaps, you will need to drill out the broken piece and retap the hole, or use a stud extractor. Consider having a tap and die set and helicoil kit on hand if working on a high-mileage car.
  • If the nut rounds off, try using a bolt extractor socket (like Irwin) or vice grips as a last resort.

Installing the GReddy Headers

With the stock manifold removed, thoroughly clean the engine block's stud threads and the exhaust port faces using a wire brush. Install new gaskets over the studs – the gasket may have a "this side up" indicator. For FA20 engines, OEM gaskets are recommended for a proper seal.

Step 1: Position the New Headers

Carefully lower the GReddy headers into place from above or below, depending on clearances. They are lighter than the stock manifold. Align the header flange holes with the studs. It helps to have a helper hold the header while you start a few nuts by hand.

Step 2: Hand-Tighten All Nuts

Start all nuts onto the studs and spin them down by hand. Use a small amount of anti-seize on the threads (but keep it off the gasket surface). Once all nuts are started, tighten them in a crossing pattern (like tightening a cylinder head) to ensure even clamping. Do not fully torque yet.

Step 3: Torque to Specification

Using a torque wrench, torque the header nuts to the manufacturer's specification. For FA20 engines, this is typically 17–22 ft-lb for the manifold nuts (check the GReddy manual). Over-tightening can warp the flange or strip threads. A common recommended sequence is to torque to 15 ft-lb in sequence, then final to 20 ft-lb. After the initial torque, go back and recheck each nut.

Step 4: Connect to Exhaust System

Slide the gasket over the header collector flange. If you are using a new gasket (often included with the headers), position it correctly. Then attach the cat pipe (or overpipe) to the header. Use new bolts and nuts; apply anti-seize to the threads. Tighten these bolts to around 30–35 ft-lb, but follow the specific instruction for your system. Do not forget to install any supplied hardware such as springs or flex joints.

Step 5: Reinstall O2 Sensors

Thread the O2 sensors into the new bungs on the GReddy headers. Use a small amount of anti-seize compound on the threads (do not get it on the sensor tip). Torque to about 25–30 ft-lb. Route the sensor wires away from moving parts and potential heat sources. Use zip ties to secure them if necessary.

Post-Installation Checks and First Start

Before lowering the car, double-check all fasteners. Reattach any heat shields that are compatible with the new headers (though many aftermarket headers discard them). Reinstall the undertray if desired. Reconnect the battery negative terminal.

Check for Leaks

Start the engine and listen for exhaust leaks. A ticking sound often indicates a leak at the header-to-engine or header-to-cat-pipe joint. Let the car idle and come to operating temperature. Use a shop rag to feel for puffs of air at the connections (be careful of hot surfaces). Alternatively, spray soapy water on the joints and watch for bubbling. If you detect a leak, tighten the offending bolts slightly (a quarter turn) – do it when the engine is cool enough to touch.

Re-Torque After Heat Cycle

After a short test drive (5–10 miles), allow the engine to cool completely. Then re-torque the header nuts and the cat-pipe bolts. The gaskets settle during heat cycling, and loosening can occur. This step is critical for a lasting seal. Many professionals recommend a second re-torque after 100–200 miles.

ECU Tuning – Absolutely Necessary

Installing free-flowing headers without an ECU tune will likely trigger a check engine light (CEL) due to the P0420 code (catalyst efficiency below threshold). The reduced back pressure changes the air-fuel ratio and can cause the engine to run lean, potentially damaging the catalytic converter or even the engine over time. To fully realize the performance gains and ensure reliability, you must have the ECU recalibrated.

Options for tuning include:

  • Custom dyno tune by a reputable Subaru tuner – best results, but expensive.
  • Open-source tuning (e.g., using RomRaider or EcuTek) with a tuning cable and software – requires skill and a wideband O2 sensor.
  • Pre-loaded OTS (off-the-shelf) tunes from companies like Tactrix or Delicious Tuning that offer header-specific maps.
  • ECU flash tool like COBB Accessport (for FA20) can run preloaded maps designed for aftermarket headers.

Without a tune, the headers will not perform optimally. You may even lose power in some areas. Invest in a proper tune to unlock the full potential.

Performance Benefits and What to Expect

After a successful install and tune, you will notice improved throttle response, a broader powerband, and a more aggressive exhaust note. Typical dyno results show gains of 10–15 whp and 8–12 wtq on a 93 octane tune. The power increase is most pronounced above 3,500 rpm, where the factory manifold becomes a bottleneck. The engine will rev more freely and feel peppier.

However, be aware of increased noise – the cabin will be louder, especially under load. Some owners install sound deadening material in the trunk area. Also, the headers will change the exhaust tone, making it deeper but potentially more drone-prone depending on the cat-back system.

Common Challenges and Troubleshooting

Fitment Issues

Some GReddy header versions may require slight clearancing of the steering shaft or underbody bracing. Check the supplied instructions carefully. If the headers contact anything, you may need a few millimeters of clearance; use a heat shield or carefully dimple the header pipe with a soft blow hammer (avoid damaging the welds).

O2 Sensor Wiring

The aftermarket header bungs may be located farther from the engine harness. Extend the O2 sensor pigtails if needed. Use heat-resistant wire and solder. Many performance shops offer pre-made extensions.

Check Engine Light after Install

If you get a CEL after the tune, it's likely a minor issue. Common codes include P0420 (catalyst efficiency) – often remedied by a tuner disabling the code via software, or a P0137 (O2 sensor slow response) – check sensor connections and ensure the bung is not too far from the engine (O2 sensor heater may struggle to reach proper temperature).

Maintenance and Long-Term Care

Aftermarket stainless steel headers are durable but can discolor slightly over time due to heat. This is normal. Check the header bolts periodically – once a year or every oil change – to ensure they have not loosened. Re-torque if needed. If you drive in salty conditions, consider ceramic coating the headers to prevent corrosion and reduce underhood temperatures.

Conclusion

Installing GReddy headers on your BRZ is a rewarding DIY project that delivers tangible performance gains and a more exciting driving experience. By following this detailed guide – with careful attention to preparation, torque specifications, and the critical need for an ECU tune – you can enjoy a successful installation and years of reliable performance. If at any point you feel overwhelmed, do not hesitate to enlist a professional exhaust shop or experienced friend. The time invested is well worth the satisfaction of a job well done and the immediate difference you'll feel behind the wheel.

For further reading on FA20 header installations and tuning, check out the FT86Club header guide and IAG Performance's installation tips.