Understanding the Role of Aftermarket Headers on Your WRX

The factory exhaust manifold on a Subaru WRX is a major restriction. It’s designed for cost, noise compliance, and thermal management, not for peak power. Replacing it with a set of COBB WRX headers (often called an “equal-length header” or ELH for later models, or unequal-length for the classic boxer rumble) unlocks significant performance potential by improving exhaust scavenging and reducing backpressure. The result is faster spool, more top-end power, and a more aggressive exhaust note. However, installation requires careful planning, precise torque, and a proper tune to realize the full benefit. This guide covers everything you need to know to install COBB headers for maximum sound and power gains.

Header Design: Equal-Length vs. Unequal-Length

Before installing, understand what you’re buying. COBB offers both unequal-length (UEL) and equal-length (EL) header options for various WRX generations.

Unequal-Length Headers (UEL)

These retain the classic Subaru boxer rumble. The unequal pulse spacing creates a deep, throaty idle and a distinctive “burble.” They sacrifice a small amount of top-end power for that iconic sound. If you prioritize the Subaru signature tone, UEL headers are your choice.

Equal-Length Headers (EL)

EL headers equalize the exhaust pulses, producing a smoother, more even sound that resembles a high-revving four-cylinder. They typically deliver better top-end horsepower and faster turbo spool due to optimized scavenging. The sound is more “European” and less distinct, but performance gains are often larger. COBB’s EL header is a popular upgrade for FA20 and FA24 WRX models.

COBB manufactures both types in T304 stainless steel with mandrel-bent tubes and thick flanges to prevent cracking. Knowing which you’re installing is critical because the process is similar, but gasket orientation and torque specs differ slightly.

Preparation: Tools, Safety, and Workspace

Proper preparation prevents leaks, broken studs, and wasted time. Plan for 4–6 hours for a first-time installation.

Required Tools and Consumables

  • Socket set: 10mm, 12mm, 14mm, 17mm deep sockets
  • Torque wrench (in-lb and ft-lb capability)
  • Breaker bar or impact gun (with proper adapters)
  • Gasket scraper or razor blade
  • Anti-seize compound (copper-based for exhaust fasteners)
  • Penetrating oil (e.g., PB Blaster or Kroil)
  • New OEM or COBB-supplied gaskets (do not reuse old ones)
  • Jack and jack stands or a lift
  • Safety glasses and gloves
  • Digital camera or phone (to document stock routing)

Vehicle Preparation

  • Work on a cold engine. Hot exhaust components can cause severe burns.
  • Disconnect the battery negative terminal to avoid shorting the O2 sensor circuits.
  • Raise the vehicle safely and support with jack stands. Never rely on a jack alone.
  • Spray all exhaust manifold studs and nuts with penetrating oil at least 24 hours before. This breaks rust and prevents broken studs.
  • Review the official COBB installation manual for your specific part number. Torque values, bolt sizes, and gasket orientation vary by model year.

Step-by-Step Installation Process

The following steps apply to most WRX platforms (GD, GR, VA, VB). Always defer to your vehicle-specific instructions.

Removing the Factory Headers

Start from the turbo side. Loosen the bolts connecting the factory header to the turbo inlet. Next, unbolt the header from the cylinder heads. You may need to remove the under-engine cover, heat shields, and sometimes the oil dipstick tube for clearance. Note: the factory header often has integrated heat shields that must be unbolted or cut off if rusted. The front O2 sensor (wideband) is located on the factory header or uppipe. Carefully unplug it and remove it with a 22mm wrench. Do not force it; use penetrating oil if seized.

Once all bolts are removed, the factory header should drop out from below. You may need to wiggle it past the steering rack and oil pan. If it sticks, check for missed bolts or heatshield interference.

Surface Preparation

This is the most common cause of exhaust leaks. Use a gasket scraper to remove all remnants of the old gaskets from the cylinder head flanges and the turbo flange. Be careful not to gouge the aluminum heads. Wipe the surfaces clean with brake cleaner. Any debris or old gasket material will cause a leak and a ticking sound.

Installing New Gaskets and the COBB Headers

Install the new gaskets dry (no sealant) unless the installation manual specifies otherwise. COBB typically does not recommend sealant. Place gaskets on the cylinder head studs, then carefully position the COBB header into place. It may require tilting and rotating to clear the oil pan and steering rack. Do not force it; if it doesn’t align, check for interference with heat shields or brackets.

Start all bolts by hand to avoid cross-threading. Tighten the cylinder head flange bolts to the specified torque (typically 25–35 ft-lb, but check your manual). Torque in a cross pattern. Next, tighten the turbo flange bolts. Reinstall the O2 sensor into the provided bung on the COBB header (often located in the collector). Use anti-seize on the O2 sensor threads to prevent future seizure.

Reassembly and Clearance Checks

Before lowering the vehicle, check all clearances. The header should not contact the oil pan, subframe, steering shaft, or any body panels. With the engine running (or using a borescope), ensure there is at least ¼ inch of clearance around hot spots. If contact occurs, loosen bolts and adjust. COBB headers are precision-bent, but minor tweaks may be needed due to chassis tolerances.

Reconnect the battery, start the engine, and check for exhaust leaks at idle. A small leak will sound like a ticking or puffing and usually requires tightening the flange bolts or re-gasketing. Do not drive the car until you are certain there are no leaks.

Maximizing Sound: Exhaust System Pairing

The header is only one part of the exhaust system. To achieve the desired sound, pair it with the right cat-back exhaust.

  • UEL + stock cat-back: Deep rumble, modest volume increase. Good for a sleeper.
  • UEL + aftermarket muffler delete: Classic boxer roar, very loud, can drone.
  • EL + resonated midpipe: Smooth, aggressive tone without excessive drone. Ideal for daily drivers.
  • EL + straight through muffler: High-pitched, race-car sound. Not recommended for street use in many areas.

Consider adding a heat shield wrap or ceramic coating to the headers. This not only reduces underhood temperatures but can slightly change the exhaust note by keeping gases hotter and flowing faster. Look into COBB’s own exhaust systems for a guaranteed match.

Maximizing Performance: The Critical Tune

Never run COBB headers on a stock ECU tune. The change in exhaust backpressure and scavenging will cause incorrect air-fuel ratios, potentially leading to knock, high EGTs, and engine damage. A proper tune recalibrates fuel, ignition timing, and boost control to take advantage of the improved flow.

COBB Accessport Tuning

The most straightforward path is using a COBB Accessport with a custom or off-the-shelf (OTS) tune from COBB. COBB provides OTS maps specifically for their headers. An OTS tune is safe and offers a good power increase, but a professional dyno tune will extract the maximum gains. Expect 15–30 whp and 20–40 lb-ft of torque depending on the turbo and supporting mods. A protuner can also dial in the idle quality and tip-in throttle response.

After flashing the tune, perform a learning drive: let the car warm up, then do several full-throttle pulls in 3rd and 4th gears to let the ECU adapt. Monitor knock correction, AFR, and boost with the Accessport. If anything looks abnormal, stop driving and consult your tuner.

Supporting Modifications

To fully use the flow potential, pair headers with a high-flow downpipe (catted or catless) and a cold-air intake. COBB offers a complete stage system. The combination of header, downpipe, intake, and an intercooler upgrade yields the best results on the FA20/FA24 engines. Learn more about tuning fundamentals to understand how each mod interacts.

Heat Management and Thermal Protection

Aftermarket headers radiate a lot of heat because they lack the heavy cast-iron heatshielding of the factory manifold. This heat can degrade nearby wiring, plastic components, and even your oil temperature. Mitigation is essential.

  • Wrap the headers with DEI titanium wrap or similar. This reduces underhood temps by 50% and can add a few horsepower by improving exhaust velocity.
  • Ceramic coating (jet-hot) is a more permanent solution. It reduces radiant heat and prevents corrosion.
  • Ensure the turbo heat shield is reinstalled or replaced with an aftermarket shield. The COBB header may require trimming of the factory shield.
  • Check the gap between the header and the oil pan. Many WRX owners add a heat blanket or reflective foil on the oil pan.

Common Mistakes and How to Avoid Them

Even experienced installers make errors. Here are the most frequent pitfalls with COBB header installations on WRX models.

Skipping the Tune

This is the #1 mistake. Without a tune, you risk detonation and melted pistons. Always flash the appropriate Accessport tune before driving.

Reusing Old Gaskets

Exhaust gaskets crush and deform during installation. Reusing them guarantees a leak. Buy new OEM or COBB gaskets. Also, check the gasket between the header and the turbo; the metal multi-layer gaskets are one-time-use.

Forgetting to Tighten Bolts After Heat Cycling

Exhaust components expand significantly. After the first 50 miles, re-torque all header bolts while the engine is cold. This prevents loosening and leaks. COBB recommends a cold re-torque procedure in their manual.

Cross-Threading Studs

The cylinder head studs are easy to cross-thread if the header is not aligned perfectly. Always start bolts by hand and check alignment before applying force. If a stud snaps, extraction requires a machine shop.

Ignoring CEL Codes

Post-installation, you might get check engine lights for catalyst efficiency or O2 sensor heater circuits. If you have a catted downpipe, the COBB tune often includes codes to disable those. If a code persists, check for exhaust leaks or sensor damage. A bad O2 sensor from heat exposure can happen if the sensor is not properly heat-shielded.

Post-Installation Inspection and Break-In

After the first drive, inspect the header flange area with the engine cool. Any black soot indicates a leak. Listen for changes in exhaust note—a sudden rasp may mean a crack or loose bolt. Record your baseline before and after with a decibel meter app; you'll be surprised by the increase.

Perform an oil change at the same time if you are due, because heat from the header can temporarily raise oil temps during installation. Use a high-quality 5W-30 or 0W-40 depending on your region.

For ongoing performance, keep an eye on the flexible exhaust hangers. A stiff new header can pull the exhaust system out of alignment, causing rattles. Replace old rubber hangers if needed. Visit COBB’s tech blog for model-specific updates.

Conclusion

Installing COBB WRX headers is one of the most rewarding modifications for sound and power. The key to success lies in meticulous preparation, proper torque, a mandatory tune, and heat management. By following the steps above and avoiding common errors, you’ll unlock the full potential of your WRX while maintaining reliability. Whether you choose the iconic rumble of unequal-length headers or the race-inspired note of equal-length, the transformation will be unmistakable every time you press the throttle.