Upgrading Your Subaru WRX: A Deep Dive into Process West Headers

Subaru WRX owners know the importance of balanced performance. The stock exhaust manifold does the job, but it leaves power and sound on the table. Process West headers offer a proven upgrade path. This article explores what makes these headers stand out, how to install them, and the real-world sound and performance results you can expect. Whether you’re a weekend wrench-turner or a serious enthusiast, this guide covers everything you need to know.

What Exactly Are Process West WRX Headers?

Process West is an Australian engineering company with a strong reputation in the Subaru aftermarket. Their WRX headers are designed as a direct replacement for the factory exhaust manifold. They are constructed from T304 stainless steel tubing and feature a tri-y or four-into-one design depending on the specific model year and application. The primary goal is to reduce exhaust backpressure and improve scavenging, which translates to increased horsepower and torque across the rev range.

Unlike some headers that prioritize top-end power at the expense of low-end torque, Process West engineers both for daily drivability. The tubing sizes are chosen to maintain exhaust velocity. The flanges are laser-cut for a perfect seal against the cylinder heads, and the collectors are mandrel-bent to ensure smooth flow. These headers are available for most Subaru EJ and FA engine platforms, including the WRX and STI models.

Key Design Features

  • T304 Stainless Steel: Resists corrosion and heat cycling better than mild steel or aluminized steel.
  • Mandrel-Bent Tubing: No crushed bends, preserving exhaust flow and preventing turbulence.
  • CNC-Machined Flanges: Flat and true surfaces eliminate leaks and maintain consistent clamping force.
  • Tri-Y or 4-1 Configuration: Optimized for the engine’s firing order and preferred power band.
  • O2 Sensor Provisions: Include bungs for factory wideband sensors, avoiding check engine lights.

Why Upgrade? Performance and Sound Benefits

The stock exhaust manifold on a Subaru WRX is cast iron. It is heavy, restrictive, and designed more for noise compliance than outright performance. Process West headers shave weight and add power. The most noticeable gains come at the upper midrange and top end, but a well-sorted header can also improve spool time if paired with a proper tune.

Dyno-Proven Horsepower Gains

Independent testing on a 2015+ WRX (FA20DIT) shows gains of roughly 15-20 wheel horsepower and 10-15 lb-ft of torque after installing Process West headers and a tune. On older EJ engines, similar gains are common, especially when combined with a cat-back exhaust and an aftermarket downpipe. The headers alone won’t turn a stock WRX into a race car, but they undo one of the biggest bottlenecks in the stock system.

The Sound Factor

Perhaps the most immediate change is the exhaust note. Stock WRX exhausts can sound flat. Process West headers introduce a rich, throaty tone with a distinctive Subaru boxer burble. The sound is more aggressive but remains civilized. There is no obnoxious drone at highway speeds, and the headers do not trigger a loudness war with neighbors. It is exactly what enthusiasts describe as "subtle sportiness." The headers add a deeper growl under acceleration without overwhelming the interior during cruising.

If you are worried about noise complaints, these headers are a safe choice. They allow the engine to breathe but keep the overall volume reasonable, especially when mated to a stock cat-back. Paired with an aftermarket exhaust, you get a more authentic sports car note without crossing into "too loud" territory.

  • Deep boxer rumble with each cylinder pulse
  • No high-pitched rasp common on cheap headers
  • Civilized cruising – no drone at 70 mph
  • Sporty growl during spirited driving

Installation: Is It Really That Easy?

Process West headers are designed for a bolt-on installation. No modifications to the factory exhaust hangers or crossmembers are required. The fitment is tight but correct, utilizing factory mounting points and securing hardware. Most owners complete the job in an afternoon with basic hand tools, a jack, and stands.

What You’ll Need

  • Socket set (10mm, 12mm, 14mm, 17mm)
  • Wrench set (combination wrenches for tight spaces)
  • Torque wrench (for final tightening)
  • Floor jack and two jack stands
  • Penetrating oil (for rusty bolts)
  • Safety glasses and mechanic gloves
  • New gaskets (often included, but have spares on hand)
  • Anti-seize compound (for threads)

Step-by-Step Walkthrough

1. Prepare the Vehicle
Park the WRX on a level surface. Disconnect the negative battery terminal to prevent any electrical shorts. Jack up the front of the car and secure it on jack stands. Always use the subframe or reinforced jack points. Remove the plastic undertray if fitted.

2. Remove the Exhaust System
Unbolt the midpipe from the catalytic converter or downpipe. Lower the exhaust system section carefully. It helps to have an extra set of hands or an exhaust hanger tool to release the rubber mounts. Set the exhaust aside.

3. Access and Remove the Manifold
The factory manifold bolts are often tight and may require penetrating oil. Soak them 10 minutes before turning. Use a breaker bar if needed. There are typically 8-12 bolts holding the manifold to the cylinder heads. There may also be bracket bolts near the turbo inlet or crossmember. Wiggle the manifold free and pull it out from below. It is heavy, so be careful.

4. Clean the Mating Surfaces
Scrape off any old gasket material using a plastic scraper or brass wire brush. Do not gouge the aluminum heads. Wipe the surfaces clean with brake cleaner and a lint-free rag. A clean seal prevents exhaust leaks later.

5. Install the Process West Headers
Position the new headers onto the studs. You may need to rotate them to clear the oil pan and steering rack. Do not force them. Install the gaskets (usually graphite or multi-layer steel) and start the nuts by hand. Tighten in a crisscross pattern to the manufacturer’s torque specification, typically around 30-35 ft-lbs for M8 studs. Refer to the included instructions. Do not overtighten.

6. Reconnect the Exhaust
Bolt the midpipe or downpipe back to the header collector. Use new gaskets and apply anti-seize to the flange bolts. Verify there is clearance around the steering shaft, subframe, and other components. Process West headers are engineered to clear, but it never hurts to double-check.

7. Reinstall the Undertray and Battery
Refit the undertray if you removed it. Reconnect the battery. Start the engine and let it idle. Check for any exhaust leaks by listening for hissing or feeling for puffs of air near the joints. A quick rev to 2500 rpm helps confirm the seal.

8. Post-Installation Check
Let the engine cool, then retorque the header bolts after a heat cycle. The gaskets will compress slightly, risking loosening. Drive the car gently for the first 50 miles, then recheck all fasteners. A second retorque after 500 miles is recommended for peace of mind.

Common Pitfalls to Avoid

  • Rushing the initial bolt removal – stripped bolts can ruin a weekend project. Use impact-rated sockets and steady pressure.
  • Forgetting the gaskets – always use new ones. Reusing old gaskets leads to leaks.
  • Cross-threading the O2 sensor – start it by hand to avoid stripping threads.
  • Neglecting to retorque after heat cycling – this step prevents gasket failure and noise.

Choosing the Right Header for Your WRX

Process West makes several header variants. The most common are the standard street header (often called the "WRX Performance Header") and the "Race" version with larger primaries for high-horsepower builds. For a daily driver with a mild tune, the street version is ideal. For a fully built engine with a big turbo, the race header maximizes flow. Check Process West’s official fitment guide to confirm compatibility with your model year and engine code.

Pro Tip: If your WRX is a 2015+ with the FA20 engine, you will need a tune to fully realize the gains. The headers change the backpressure enough that the stock ECU can pull timing. A simple accessport tune or professional dyno tune is highly recommended. For EJ engines, tuning is strongly advised but not strictly mandatory, though you may see a check engine light for the catalyst efficiency monitor.

Comparing Process West to Other Options

Several brands compete in the Subaru header market, including Killer B Motorsport, Cobb Tuning, and Perrin. Killer B headers are premium equal-length designs made from coated steel, known for high-end flow but also a higher price. Cobb headers are budget-friendly and do the job, but they are not as well-engineered for clearance. Process West strikes a balance between price, quality, and sound. They offer the classic boxer rumble (due to their unequal-length design in many versions) and robust construction without the sticker shock of boutique brands.

Another consideration is equal-length vs. unequal-length headers. Equal-length headers sacrifice the boxer burble for pure flow, used on race cars. Unequal-length headers keep the iconic sound. Process West offers both, but most enthusiasts choose their unequal-length design for that classic Subaru growl.

Maintenance and Longevity

Stainless steel headers will develop a golden or blue patina over time from heat. This is normal and does not affect performance. However, stainless steel can crack if exposed to thermal shock. Avoid puddles or high-pressure water on hot headers. After a spirited drive, let the engine idle for a minute before shutting off to allow heat to dissipate evenly. Periodically check the flange bolts for tightness, especially after initial installation. Gaskets should be replaced every few years or if you notice a leak. With proper care, Process West headers will outlast the life of the car.

Taking the Next Step

Installing Process West WRX headers is one of the most satisfying bolt-on upgrades you can do. The performance gain is real, the installation is manageable for a DIYer, and the sound is exactly what Subaru fans want. Whether you are aiming for a mild street improvement or building a weekend track car, these headers are a solid foundation.

For more details, visit the official Process West website for product specifications and application guides. You can also find install diaries and owner reviews on Subaru enthusiast forums and NASIOC. If you are ready to purchase, check with reputable retailers like Import Image Racing or MAPerformance for pricing and availability.

Conclusion

Upgrading to Process West WRX headers delivers a noticeable improvement in engine responsiveness, horsepower, and sound. The installation is straightforward enough for most home mechanics, and the result is a more engaging driving experience without the drawbacks of an excessively loud exhaust. For Subaru owners who want a subtle sporty upgrade that performs as good as it sounds, Process West headers are an excellent choice. They blend engineering quality with the classic boxer burble, making every drive more rewarding.