Wrx Headers Installation Tips: Step-by-step Guide for Brand-specific Fitment

Installing aftermarket headers on a Subaru WRX is a popular upgrade that can unlock meaningful gains in both power and exhaust note. Headers reduce exhaust backpressure, allowing the engine to breathe more freely, which often results in a bump of 10–20 horsepower and a more aggressive sound. However, the installation process requires careful attention to detail—especially because different header brands have unique fitment characteristics. This guide provides a comprehensive, step-by-step walkthrough for installing WRX headers, with brand-specific tips to help you avoid common pitfalls and achieve a leak-free, long-lasting install.

Understanding WRX Headers

WRX headers come in two main configurations: equal length and unequal length. Equal length headers, such as those from Killer B Motorsport, balance exhaust pulses for more consistent torque and a smoother sound—similar to a typical inline-four. Unequal length headers, like the factory units, retain the classic Subaru rumble at the expense of some top-end power. Material choices also matter: 304 stainless steel headers offer high corrosion resistance and a bright finish, while ceramic-coated headers reduce under-hood temperatures. Regardless of design, all headers must fit the port spacing of the Subaru EJ or FA engine precisely. Poor fitment leads to exhaust leaks, persistent Check Engine Lights, and even cracked flanges.

Tools and Materials Needed

Before starting, gather the following tools and supplies. Having everything on hand prevents mid-project trips to the hardware store.

• Socket set – 10mm, 12mm, 14mm, and 17mm sockets; a 12-point 12mm socket helps with some header bolts.
• Torque wrench – ⅜‑inch drive, ranging from 10 to 80 ft‑lb.
• Ratchet extensions – 3-inch and 6-inch extensions make it easier to reach studs near the block.
• Header gaskets – OEM or high-quality aftermarket (e.g., Grimmspeed multi-layer steel).
• Exhaust sealant – High-temp copper or ultra-copper RTV for gasket edges.
• Penetrating oil – WD‑40 or PB Blaster for rusted nuts and studs.
• Anti-seize compound – Applied to stud threads during reassembly.
• Jack and jack stands – A 2‑ton low-profile jack with two stands rated for your vehicle.
• Oxygen sensor socket – 22mm or 7/8″ crowfoot for O₂ sensor removal.
• Shop towels and gloves – Exhaust work is dirty.
• Flashlight or work light – Many header bolts are hidden in shadows.

Safety Precautions

Working on an exhaust system involves hot components and heavy parts. Follow these safety rules:

• Disconnect the battery negative terminal to prevent accidental shorting or starter engagement.
• Allow the engine and exhaust to cool completely before beginning—surface temps can exceed 500°F.
• Use jack stands rated for your WRX’s weight; never rely solely on a hydraulic jack.
• Wear safety glasses to protect against falling debris and rust particles.
• Work in a well-ventilated area. Exhaust fumes are toxic even when the car is off (residual fuel vapors).

Step-by-Step Installation Process

Step 1: Prepare Your Workspace

Clear the area of clutter and ensure you have enough room to slide under the car. Lay out all tools and new parts. Check the new headers against your vehicle’s engine bay: confirm port alignment, the presence of bungs for exhaust gas temperature or oxygen sensors, and the downpipe flange orientation.

Step 2: Lift the Vehicle

Drive the WRX onto ramps if available, or use a jack to raise the front. Place jack stands under the reinforced frame rails just behind the front wheels. Shake the vehicle to verify stability. You’ll need clearance to access the under-engine exhaust components, so aim for at least 18 inches of lift.

Step 3: Remove the Old Headers

Begin by disconnecting the battery. Then remove any heat shields that cover the factory headers—they are usually held on by 10mm bolts. Next, if your WRX has an unmodified exhaust, spray all header-to-engine studs and the downpipe bolts with penetrating oil. Wait 10 minutes.

Unbolt the downpipe from the header (or from the turbo, depending on your generation). Use a 12mm or 14mm socket for these nuts. Carefully disconnect the front oxygen sensor wiring harness, then remove the sensor itself with the O₂ socket.

Now tackle the header-to-cylinder head bolts. There are typically 12 bolts (three per cylinder) on EJ engines, or 8 bolts on FA engines. Work in a crisscross pattern to relieve tension evenly. Lift the old header out from the top through the engine bay or from below—depending on clearance. It may need to be twisted and pulled sideways past the oil pan. Take care not to damage the studs or the fuel lines above.

Step 4: Inspect and Prepare the New Headers

Visually inspect the new headers for cracks, welding defects, or warped flanges. Lay them on a flat surface and check that the flange faces are straight. Apply a thin bead of exhaust sealant around the port openings of the header gaskets—this helps prevent small leaks. Place the gaskets onto the studs with the metal side facing the cylinder head.

For the header-to-header and header-to-downpipe connections, apply anti-seize to the threads of all bolts. If your headers came with new studs, install them now with a drop of threadlocker (medium strength, 242) to prevent loosening from vibration.

Step 5: Install the New Headers

Position the headers under the car or through the engine bay opening. Align them onto the studs carefully—do not force them, or you may bend a stud. For most WRX header designs, the left (driver side) bank slides in first, then the right bank, with the crossover pipe connecting under the oil pan. Hand-tighten all bolts until snug, but do not fully tighten yet.

Connect the downpipe to the header collector loosely with the supplied gasket and hardware. This ensures the header can still shift slightly for final alignment. Check for any contact between the header tubes and steering shaft, oil pan, or subframe. If you find interference, loosen the header bolts and reposition the assembly.

Step 6: Torque the Bolts

Using a torque wrench, tighten the header-to-cylinder head bolts in the correct sequence (usually from the center outward) to 35–40 ft‑lb for most aftermarket headers. Always consult the brand’s accompanying instructions; some manufacturers recommend lower values (28–32 ft‑lb) to avoid pulling threads in the aluminum cylinder head. Re-torque after the first heat cycle (see “Testing” below).

Torque the downpipe-to-header bolts to 35–40 ft‑lb and the header crossover connections to 30–35 ft‑lb.

Step 7: Reconnect Exhaust Components

Reinstall the front O₂ sensor into its new bung using anti-seize on the threads. Torque to 30 ft‑lb. Reattach the sensor wiring and secure it away from hot header tubes with zip ties.

If your new headers included heat shields, install them now. Otherwise, you can reuse the factory heat shields (some trimming may be necessary). Reconnect the battery.

Step 8: Lower the Vehicle and Final Checks

Remove the jack stands and lower the car. Turn the steering wheel fully left and right to confirm the headers do not contact the steering shaft or sway bar. Inspect all hoses, lines, and wiring for proximity to the headers; reroute or wrap any components that are within 1 inch of the exhaust.

Step 9: Test the Installation

Start the engine and let it idle. Listen for hissing or ticking sounds—these indicate exhaust leaks. Use a glove (or an old rag) to seal the tailpipe for a moment; if the engine stumbles and dies, you have a leak upstream. Spray a mix of soapy water around each header-to-head joint and the collector; bubbles confirm escaping gas. Tighten any loose bolts immediately (after the engine has cooled).

After a 20-minute heat cycle, allow the engine to cool and re-torque all header bolts to spec. This second torque pass accounts for thermal expansion and gasket settling.

Brand-Specific Fitment Tips

Brand A: Equal Length Performance Headers

Brand A headers (e.g., Tomei or A’PEXi equal-length designs) are precision-formed from 321 stainless steel. They fit most 2002–2014 WRX/STIs without major modification, but the collector often sits very close to the oil pan. Tip: Use a thin 5mm spacer on the oil pan bolt that faces the collector to prevent metal-on-metal contact. Torque the header bolts to 32 ft‑lb maximum to avoid stressing the thin flanges. Do not reuse the factory gaskets; these headers require specific copper or multi-layer steel gaskets.

Brand B: Unequal Length Rumble Headers

Brand B headers (like OEM-style aftermarket copies from companies such as Borla or Invidia) preserve the classic Subaru flat‑four rumble. They are typically thicker-walled and heavier. Installation may require dropping the subframe slightly to slip the driver‑side header past the suspension crossmember. Tip: Apply anti-seize liberally to the downpipe bolts because unequal-length headers generate more heat and can seize. Check the primary tube lengths: if one bank’s tube is significantly longer, you may need to trim the downpipe flange by 1–2mm for a proper seal.

Brand C: Motorsport‑Grade Long‑Tube Headers

Brand C headers (e.g., Killer B Motorsport Ultimate) are designed for full‑race applications and often include a 3‑inch collector and a V‑band downpipe connection. These headers are tall and may interfere with the hood or intercooler piping on WRX models with stock turbo locations. Tip: Before installing, test‑fit the header with the intercooler removed. You may need to reinforce the engine mounts (Group N mounts) to provide enough clearance. Use the supplied high‑temp gaskets and do not apply sealant; the multi‑layer metal gasket is designed to seal dry. Torque to the higher end of the spec (38–40 ft‑lb).

Common Installation Challenges and Solutions

After Installation: ECU Reset and Tuning Considerations

Installing headers changes exhaust velocity and oxygen sensor readings. On 2002–2014 WRX models with a stock ECU, the car will often run rich at idle and may trigger a P0420 catalyst efficiency code. Perform a hard ECU reset: disconnect the battery, pump the brake pedal three times, and wait 10 minutes before reconnecting. Drive the car for 50–100 miles under varying load to allow the ECU to relearn fuel trims.

For best results, especially with equal-length headers, consider an ECU reflash or a tune via an Accessport. A custom tune can adjust fuel tables and cam timing to capitalize on the increased exhaust flow, often yielding an additional 10–15 whp over a simple bolt‑on installation.

Conclusion

Installing WRX headers is a rewarding project that can sharpen throttle response, add a distinctive exhaust note, and free up horsepower. The key to a trouble‑free installation lies in thorough preparation, attention to torque specs, and understanding the quirks of different brands. By following the step‑by‑step process above—paying special attention to gasket condition, bolt sequences, and clearance checks—you can avoid common mistakes and enjoy a performance‑grade exhaust system that lasts for years. Always re‑torque the bolts after the first heat cycle and monitor your OBD‑II system for any emissions‑related codes.

For additional reference, consult the NASIOC header installation guide and the official Cobb Tuning installation resources for torque specs that apply to your specific model year. As always, when in doubt, seek professional installation from a shop experienced with Subaru aftermarket exhaust work.