Introduction

The Subaru BRZ is a platform that rewards careful modification. Among the most impactful changes you can make to its FA20 or FA24 engine is upgrading the exhaust headers. The stock manifold is a cast-iron or welded unit that prioritizes low-cost manufacturing and NVH suppression over outright performance. Swapping to a set of aftermarket headers directly addresses the most restrictive part of the exhaust system, improving flow, reducing backpressure, and extracting genuine power gains. This article explains the science behind exhaust flow, evaluates header designs, provides a detailed installation guide, and covers tuning and maintenance considerations so you can make an informed upgrade.

Understanding Exhaust Flow and Its Importance

How Exhaust Flow Affects Engine Performance

Every four-stroke cycle ends with the exhaust stroke: the piston pushes spent gases out of the cylinder and into the exhaust manifold. If the manifold creates resistance—sharp bends, unequal tube lengths, or small cross-sections—the engine must work harder to expel those gases. This pumping loss robs power. Improved exhaust flow reduces the pressure differential across the exhaust valves, allowing the engine to spin more freely and produce more torque, especially in the mid- to high-RPM range.

The Role of Scavenging

Beyond simple flow, header design influences a phenomenon called exhaust scavenging. When one cylinder’s exhaust pulse travels down the primary tube, it creates a low-pressure wave that can help draw gases from a neighboring cylinder. This effect is strongest when tube lengths are carefully matched—hence the benefit of equal-length headers. On the Subaru BRZ, which uses a boxer engine, the left and right cylinder banks have separate header collectors. Properly tuned primaries can significantly improve cylinder filling and power output.

Backpressure Myths

A common misconception is that engines need some backpressure to run well. In reality, engines need exhaust velocity, not backpressure. For naturally aspirated engines, the goal is to maintain gas velocity to keep the scavenging effect strong, but any restriction that adds backpressure is harmful. Aftermarket headers remove those restrictions while preserving or increasing velocity through proper tube sizing. Modern ECU tuning can then adjust fuel and ignition timing to fully exploit the improved flow.

Benefits of Aftermarket Headers

Measurable Power Gains

On a stock Subaru BRZ, aftermarket headers typically provide 10–15 whp and a similar increase in torque. With a full exhaust system (header, front pipe, cat-back) and a tune, those gains can reach 20–25 whp. The power increase is most noticeable above 4,000 rpm, where the engine’s torque curve flattens with stock exhaust. Aftermarket headers allow the engine to continue building power to redline.

Audible Transformation

The boxer engine has a distinct rumble, especially with unequal-length headers. Aftermarket headers change the exhaust note significantly. Equal-length headers produce a smoother, more consistent tone, while unequal-length headers preserve the classic Subaru burble. Many enthusiasts prefer the latter for its aggressive character. Either way, the sound becomes louder and more present inside and outside the car.

Weight Reduction

Stock exhaust manifolds on the BRZ are cast iron, heavy, and heat-soak prone. Aftermarket headers made of 304 stainless steel or even titanium can save 5–10 lbs. While not massive, that weight is unsprung and located near the engine’s center of gravity, which contributes to sharper handling.

Thermal Management

Most aftermarket headers are wrapped or coated to reduce under-hood temperatures. This prevents heat from radiating into the intake tract and cooling system, helping maintain consistent intake air temperatures (IAT) and reducing the risk of heat soak during track sessions. Some headers even incorporate integrated heat shields.

Choosing the Right Headers for Your Subaru BRZ

Material Selection

Stainless Steel (304): The most common option. It resists corrosion, can be polished or left raw, and offers a good balance of cost and durability. Mild steel is cheaper but rusts quickly, especially in winter climates.

Titanium: Lighter and with unique aesthetics (blue/rainbow heat tint), but 2–3x more expensive. Titanium headers are often used in competition builds.

Inconel: Extremely high heat tolerance, but rare on street cars due to cost. Not recommended for most BRZ owners.

Equal-Length vs. Unequal-Length (EL vs. UEL)

Equal-Length (EL): Primaries are the same length, maximizing scavenging efficiency and producing a more linear power band. The sound is smoother, often described as “Ferrari-like.” Many tuners prefer EL headers for consistent cylinder-to-cylinder flow. Available from brands like Tomei, JDL, and ACE.

Unequal-Length (UEL): Primaries are different lengths, which preserves the signature Subaru boxer rumble. UEL headers sacrifice some top-end power for a more aggressive mid-range torque curve. However, modern UEL headers have improved scavenging compared to older designs. Popular options from Grimmspeed, Borla, and Perrin.

Primary Tube Diameter and Wall Thickness

For a naturally aspirated FA20/FA24, 1.5″ to 1.625″ inner diameter is ideal. Too large and exhaust velocity drops, hurting low-end torque. Too small and flow restriction remains. Wall thickness: 16-gauge (0.065″) or 18-gauge (0.049″) is common. Thicker walls resist cracking but add weight; thinner walls save weight but can fatigue over time near the collector.

Collector Design and Flanges

Most BRZ headers use a merge collector where four primary tubes combine into a single collector, then connect to the front pipe via a V-band or two-bolt flange. V-bands are easier to seal and align. Ensure the header includes a proper donut gasket or flat flange compatible with your front pipe.

Coating and Wrapping

Ceramic coating (e.g., Jet-Hot) inside and out reduces radiant heat and slows cooling, which keeps exhaust velocity higher. Wrapping with DEI or Thermo-Tec fiberglass is effective but can trap moisture and promote corrosion if the header isn’t stainless. Wrap is best for track-only cars; ceramic coating is better for daily drivers.

Installation Guide for Aftermarket Headers

Tools and Consumables

  • Metric socket set (10mm, 12mm, 14mm, 17mm) and wrenches
  • Torque wrench (range 10–50 ft-lbs)
  • Breaker bar and extensions
  • Penetrating fluid (PB Blaster or equivalent)
  • Anti-seize compound (copper or nickel-based)
  • New exhaust gaskets (manifold-to-head and collector gaskets)
  • Jack and jack stands (4-point preferably)

Step 1: Safety and Preparation

Park on level ground, disconnect the battery negative terminal, and allow the engine to cool completely. Raise the car securely on jack stands. Remove under-engine covers if equipped.

Step 2: Remove the Stock Header

Unbolt the front pipe from the stock header collector (three nuts, 14mm). Disconnect the oxygen sensors carefully using an O2 sensor wrench or socket—heat cycles cause them to seize. Remove the heat shield covering the primary tubes. Unbolt the stock manifold from each cylinder head (10mm bolts, usually 3 per bank). The driver’s side bank may require removing the alternator for clearance; the passenger side may require removing the airbox and intake duct. Lower the stock header out from below.

Step 3: Inspect and Prep the New Header

Check the new header for casting sand, burrs, or debris. Apply anti-seize to all thread points that will contact exhaust gas (except O2 sensor threads—use anti-seize sparingly). Install the supplied gaskets onto the cylinder head studs.

Step 4: Install the Aftermarket Header

Position the header from below, ensuring it clears the subframe and oil pan. For EL headers with a single collector, the left bank will need to be guided into position first. Hand-tighten all head flange bolts, then torque to 18–20 ft-lbs in a crisscross pattern. Reattach the front pipe using a new gasket; torque collector bolts to 30–35 ft-lbs.

Step 5: Reconnect Oxygen Sensors and Hardware

Reinstall O2 sensors. If the new header removes the secondary cat (catless), you may need a spark plug non-fouler or a tune to avoid a Check Engine Light (CEL). Secure the harness with zip ties away from hot surfaces. Reinstall the alternator, airbox, and any other components removed. Double-check all connections for clearance—header tubes should not contact the steering shaft, transmission bell housing, or frame rails.

Step 6: Start-Up and Leak Check

Reconnect the battery. Start the engine and let it idle. Listen for exhaust leaks—a ticking sound near the flanges indicates a gasket leak. Use a smoke machine or soapy water to pinpoint leaks. Shut off the engine and retighten any loose bolts after the first heat cycle (cool down).

Tuning and ECU Considerations

Why You Need a Tune

Installing aftermarket headers—especially catless ones—will change the air-fuel ratio and exhaust backpressure. The factory ECU may detect increased flow via the MAF sensor and attempt to compensate, but it cannot fully optimize timing and fuel maps. A custom tune (via OpenFlash Tablet, ECUTek, or Cobb Accessport) is essential to unlock the full power potential and prevent lean conditions that can cause engine damage.

O2 Sensor Calibration

Catless headers cause the secondary O2 sensor (post-cat) to read a lean mixture, triggering a P0420 code (catalyst efficiency below threshold). A tune can code out the post-cat sensor, or you can use a mechanical spacer (defouler) to pull the sensor out of the exhaust stream. For a reliable street car, tuning is the better approach.

E85 and Higher Octane Tunes

With headers and a tune, the FA20/FA24 responds well to E85, which provides additional knock resistance and allows more aggressive ignition timing. Expect 25–30 whp over a pump-gas tune. However, E85 requires upgraded fuel injectors and pump on earlier BRZs (2013–2016).

In many states and countries, removing catalytic converters (catless headers) violates emissions regulations. Vehicles must retain the same number of converters as delivered. Catless headers will fail visual inspection in California (SMOG check) and many other regions. Consider high-flow catted headers (e.g., Grimmspeed catted header) if you need to pass emissions. These preserve some emissions equipment while still improving flow.

Maintenance and Longevity

Heat Cycling and Cracking

All headers will crack eventually if subjected to repeated thermal shock. Stainless steel with good welding and proper support brackets lasts longer. Avoid headers with sharp 90-degree bends or thin tube walls. Check header bolts every 5,000 miles for loosening; retorque if necessary. Some owners use stage-8 locking header bolts to prevent loosening.

Rust and Corrosion

If you drive in winter conditions, ceramic-coated or titanium headers resist rust better than raw stainless. Wipe down headers occasionally if you live near saltwater. Avoid using steel wool on stainless; use a fine brass brush.

Heat Management Long-Term

Re-wrap the header every 2–3 years if using fiberglass wrap, as it degrades. Ceramic coating lasts indefinitely but can chip if struck by road debris. Consider adding a turbo blanket-style heat shield over the collector area.

Conclusion

Aftermarket headers are a foundational upgrade for any Subaru BRZ owner seeking real performance. By reducing backpressure, improving scavenging, and lowering weight, they transform the engine’s character. The choice between EL and UEL, material, and coating depends on your goals—be it maximum top-end power, that classic Subaru rumble, or emissions compliance. Pair headers with a professional tune and proper installation, and your BRZ will reward you with sharper throttle response, more power, and a soundtrack that turns heads. For more information, consult owner forums like FT86 Club and the Subaru Performance Parts catalog for recommended pairings.