Tools and Materials Needed

Having the right tools on hand will keep the job moving smoothly and prevent frustrating stops. You can often rent specialty tools at auto parts stores if you don't own them outright.

  • Complete socket and wrench set (metric, 10 mm, 12 mm, 14 mm, 17 mm, 19 mm, and a 22 mm for oxygen sensors if you are replacing them)
  • Breaker bar (for stubborn rusted fasteners)
  • Torque wrench (range 15–100 ft-lb)
  • Jack and two sturdy jack stands (minimum 3-ton capacity)
  • Exhaust hanger removal tool (or large flat-head screwdriver and pliers)
  • Penetrating lubricant (WD-40, PB Blaster, or equivalent)
  • New exhaust gaskets (turbo-to-downpipe, downpipe-to-midpipe, midpipe-to-axle-back; verify size and shape for your year/model)
  • Replacement nuts and bolts (exhaust-grade stainless or copper anti-seize coated)
  • Oxygen sensor socket (22 mm O2 sensor socket with a cutout for the wiring, especially if you have a wideband sensor)
  • Anti-seize compound (for threads to prevent future seizing)
  • Safety glasses and mechanic’s gloves
  • Lubricant spray (silicone or penetrating oil for rubber hangers)

Preparation and Safety Precautions

Begin by parking your WRX on a flat, level concrete floor where you can safely lift it. If the car has been driven recently, allow the exhaust system to cool completely – a hot system can cause severe burns and makes gaskets difficult to align. Put on safety glasses and gloves before you start. Disconnect the negative battery terminal if you plan to remove any oxygen sensors, to avoid shorting the sensor heater circuits. For 2015+ WRX models, also consider disconnecting the battery before working near the turbo area to prevent accidental airbag sensor activation.

Safety note: never work under a vehicle supported only by a jack. Use properly rated jack stands on the vehicle’s frame points or pinch welds. A second set of stands under the rear subframe adds extra stability when working on the exhaust.

Vehicle Lift Points (for 2015–2021 WRX)

The front lift point is the central crossmember near the oil pan. The rear lift point is the rear differential. Place jack stands under the side frame rails behind the front wheels and in front of the rear wheels. For better access to the exhaust hangers near the rear, you may also lift the car by the rear differential and place stands under the rear subframe.

Step-by-Step Removal of the Factory Exhaust

This general procedure works for both OEM systems and many aftermarket turbo-back setups. Specific clamp and hanger positions differ between 2002–2014 and 2015–2021 WRX generations, but the core steps are identical.

Step 1 – Disconnect Oxygen Sensors (If Necessary)

Locate the upstream and downstream oxygen sensors. On Subaru turbo-back systems you typically have one sensor near the turbo (front O2) and one in the downpipe (rear O2). Spray the sensor threads with penetrating lubricant 15 minutes before removal. Using the O2 sensor socket or a 22 mm wrench, carefully unthread each sensor. If they are tight, work slowly to avoid stripping the threads in the downpipe. Place the sensors aside on a clean rag.

Step 2 – Support the Exhaust and Remove Hangers

Place a jack (with a block of wood) under the center muffler or resonator to support weight. Starting at the rear, spray the rubber exhaust hangers with silicone lubricant. Use an exhaust hanger removal tool or a large flat-head screwdriver to pry the hanger rods out of the rubber mounts. There are typically 4–6 hangers: two near the rear mufflers, two on the center resonator/midpipe, and two on the downpipe. Remove all hangers so the exhaust is hanging only by the flange bolts. Do not let the system hang unsupported – it can damage the flex section of the downpipe.

Step 3 – Unbolt the Flanges

Starting from the turbo-to-downpipe connection at the back of the turbocharger, use a socket and breaker bar to remove the two or three bolts securing the downpipe to the turbo. Then unbolt the downpipe-to-midpipe connection (usually two bolts) and finally the midpipe-to-axle-back connection (two bolts on each side if dual exhaust). With all bolts removed and the hangers disconnected, carefully lower the entire exhaust system from the jack. Watch for any remaining hangers – on WRX models with a center brace, you may need to remove a bolt near the transmission crossmember.

Step 4 – Clean Mounting Surfaces

Once the old exhaust is out, use a wire brush or abrasive pad to clean the turbo outlet flange, downpipe flange, and midpipe flanges. Remove all traces of old gasket material and any rust scale. A clean surface is critical for a leak-free seal with new gaskets. Wipe the area with brake cleaner to remove oil or grease.

Installing the New Turbo-Back Exhaust

Whether choosing an OEM replacement or an aftermarket system, the installation process follows the same order: downpipe → midpipe → axle-back. Use new gaskets at every connection – never reuse old gaskets, as they will compress unevenly and lead to exhaust leaks. Apply a thin coat of copper or anti-seize to the bolt threads (unless the hardware is pre-coated).

Step 5 – Install the Downpipe

Slide the new downpipe onto the turbo outlet studs. On aftermarket downpipes, you may need to slightly rotate the pipe to clear the transmission case or the wastegate actuator. Use new gaskets – the standard is a multi-layer steel (MLS) gasket for turbo-to-downpipe. Hand-tighten all bolts, then torque to 30–35 ft-lb (check manufacturer specs; for OEM Subaru it is 32 ft-lb). For aftermarket downpipes with a separate flex section, ensure the flex joint is aligned to reduce vibration. Do not fully tighten the lower downpipe flange until the midpipe is attached.

Step 6 – Connect the Midpipe

Attach the midpipe to the downpipe’s rear flange. Use a new gasket – many aftermarket systems use a 3-inch flat gasket. Loosely install the bolts. If your midpipe includes a resonator or a high-flow catalytic converter, ensure it is oriented correctly and that the hanger rods point upward toward the chassis. Attach the rubber hangers to the new midpipe’s hanger rods. Do not snap the hangers in yet – just slip them on loosely. Repeat for any other center hangers. Tighten the midpipe-to-downpipe bolts to 30 ft-lb.

Step 7 – Install the Axle-Back Section

Now attach the axle-back (muffler) section to the midpipe. Again use a new gasket. Slide the two halves together, then attach the hanger rods to the rubber isolators. On dual-exit systems, fit both mufflers and connect them with a cross-pipe if applicable. Hand-tighten the bolts, then torque to 25–30 ft-lb. Check that the exhaust tips are centered in the bumper cutouts – loosen the bolts and shift the mufflers if needed.

Step 8 – Tighten All Remaining Connections

With the entire system loosely assembled, go back and fully tighten every bolt and clamp. Start at the turbo flange, then work rearward. Use your torque wrench on all bolted flanges. For band clamps (common on aftermarket V-band systems), tighten to the manufacturer’s value – often 40–50 ft-lb, but always check the included instructions. Over-tightening band clamps can crack the pipe.

Step 9 – Reinstall Oxygen Sensors

Reinstall the oxygen sensors into their bungs. Apply a small amount of anti-seize to the threads (if using a new sensor, skip this as they come pre-coated). Torque to 25–30 ft-lb. On aftermarket downpipes, the rear O2 bung may be located further downstream – you may need a sensor extension harness if the factory harness does not reach. Most quality aftermarket systems include an extension.

Step 10 – Final Inspection and Engine Start

Double-check all connections: ensure no hangers are missing or twisted, and that the exhaust is not contacting the underbody, driveshaft, or any heat shields. Check that all bolts are tight but not stripped. Reconnect the negative battery terminal. Start the engine and listen for any ticking or whooshing sounds indicating a leak near a flange. A common leak source is the turbo-to-downpipe gasket – if you hear a high-pitched whistle, shut off the engine and re-torque those bolts. Allow the car to reach operating temperature and check for exhaust smoke from under the car.

Lower the vehicle carefully, then take it on a short test drive. Listen for any rattles or abnormal drone. After a few miles, park on a level surface and re-check all bolts – some aftermarket systems require a re-torque after initial heat cycles.

OEM vs. Aftermarket Turbo-Back Exhaust Options

Choosing between a factory replacement and an aftermarket system involves trade-offs in sound, weight, power gains, legality, and cost. Below is an expanded comparison to help you decide based on your goals.

OEM Subaru Exhaust (Factory Replacement)

A genuine OEM turbo-back exhaust is designed to meet strict noise regulations and emissions requirements. It uses relatively small pipe diameters (often 2.5 inches on older WRX models, ~2.75 inches on newer ones), restrictive catalytic converters, and heavy mufflers. Benefits include:

  • Fully emissions-legal – retains all catalysts and meets EPA/CARB standards for street use.
  • Factory fitment guaranteed – no modifications needed, hanger positions are perfect.
  • Quiet interior and exterior – no drone at highway speeds.
  • Longevity – stainless steel construction (though some sections are aluminized steel on older cars).

Drawbacks: minimal performance gains, heavy (often 40+ pounds more than aftermarket), and expensive when purchased new from the dealer. An OEM system is best for drivers who want a stock experience or need to pass strict noise inspections.

Aftermarket Turbo-Back Options

Aftermarket systems from brands like COBB, Injen, Mishimoto, AWE, Borla, and ETS offer substantial improvements in flow, weight savings, and sound tuning. Most are TIG-welded 304 stainless steel (some with 3-inch or 3.5-inch piping). Key considerations:

Full Turboback vs. Downpipe + Cat-Back

A true turbo-back system replaces all piping from the turbo outlet to the tailpipes. Some owners prefer a downpipe paired with a separate cat-back. A full system ensures optimal diameter and tuning, but mixing brands can cause fitment issues at the midpipe connection.

Catalytic Converter Configuration

Aftermarket downpipes come in catted (high-flow catalytic converter) and catless versions. Catted downpipes reduce rasp and keep the check engine light off with proper tuning, while offering more flow than OEM. Catless downpipes maximize flow and spool but produce a louder, more aggressive tone and may trigger a P0420 code without an O2 sensor spacer or tune. Note that removing the catalytic converter is illegal for street use in many regions and can lead to emissions test failure.

Sound and Drone

Aftermarket systems produce a deeper, louder tone. The resonator and muffler design control drone: Helmholtz-style resonators or J-pipes can cancel out 2000–3000 RPM drone. Listen to sound clips from reputable brands to find your preferred note – some are “mature” and refined, others pure race-car.

Weight Savings

A full 3-inch aftermarket turbo-back can shed 15–25 pounds of unsprung weight compared to the heavy factory system. This reduces inertia and improves handling response in addition to power gains.

Performance Gains

With a proper tune, a turbo-back exhaust can add 30–50 whp on a WRX (depending on turbo size and fuel). Even without tuning, you may see a 10–15 hp gain due to reduced backpressure. A dyno tune is strongly recommended to adjust air-fuel ratios and avoid running lean.

Tuning Requirement

Most aftermarket downpipes increase flow enough that the ECU’s fuel and timing maps need adjustment. A common solution is an Accessport (COBB or Open Source) flashed with an off-the-shelf (OTS) map designed for your specific turbo-back setup. For best results and safety, schedule a professional dyno tune.

Warranty Considerations

Installing an aftermarket exhaust may void the factory warranty on the exhaust system and could affect related components. Check your vehicle’s warranty terms before proceeding.

Before purchasing an aftermarket turbo-back, understand local laws. In the United States, removing or replacing catalytic converters is illegal under the Clean Air Act unless the replacement is certified as meeting Tier 2 standards. Most high-flow cats are not approved for street use – they are for off-road/competition only. Many states (California, New York, Colorado, etc.) enforce visual inspections and OBD II readiness checks during emissions testing. A catless downpipe will fail an OBD II plug-in test if a CEL is present.

If you live in an emissions-testing area, a catted aftermarket downpipe combined with a good tune (which disables the P0420 code) is your best option. Keep the factory downpipe to swap back for inspection. Several online vendors offer “state-legal” high-flow cats that claim to pass – research reviews for your specific model year.

Common Installation Issues and Troubleshooting

Even with careful planning, you may encounter these pitfalls:

  • Stuck bolts on turbo flange: These are notorious for seizing after years of heat cycles. Apply penetrating spray the night before, and use a breaker bar. If a bolt snaps, you may need to extract the stud – consider replacing turbo-to-downpipe studs with new ones if they look weak.
  • Hanger difficulty: Rubber hangers on older cars can become brittle. Use a small flat-blade screwdriver to spread the rubber slit and lubricate generously. If they tear, replace them for $5–10.
  • Exhaust hitting subframe or underbody: Midpipe or downpipe contact with the transmission crossmember or front crossmember can cause vibration. Adjust hangers or add a small spacer (washer) at the hanger mount. Some aftermarket systems include an adjustable midpipe.
  • Drone at specific RPM: If the exhaust is too loud inside the cabin, consider adding a resonator or a Helmholtz quarter-wave pipe. Some brands sell add-on resonators that weld in.
  • Oxygen sensor error: P0420 (insufficient catalyst efficiency) is common with catted or catless downpipes. A tune with CEL delete or an O2 sensor spacer (angled bung) often resolves it. For catless, the spacer may need a mini-cat built in.

Maintenance and Longevity Tips

After installation, protect your investment:

  • After the first 500 miles, recheck all bolts and clamps – heat cycling can loosen connections.
  • Clean the exhaust tips with a stainless steel cleaner monthly to prevent yellowing.
  • If you drive in winter, consider applying a light coating of anti-seize on all exposed threads (downpipe-to-turbo) to ease future removal.
  • Inspect rubber hangers every oil change – silicone aftermarket hangers resist heat and sagging better than OEM rubber.
  • Keep the stock exhaust in storage in case you need to revert for resale or legal reasons.

For detailed torque specifications and fitment guides, consult: Subaru Official Performance Parts. For aftermarket product comparisons and dyno charts, COBB Tuning offers comprehensive tuning hub guides. The IWSTI / WRX forums provide real-world owner experience with dozens of turbo-back installs and sound clips. For federal legal information regarding aftermarket exhaust systems, the EPA’s policy on aftermarket parts is also helpful reading.

Conclusion

Installing a turbo-back exhaust on your Subaru WRX is one of the most rewarding modifications you can perform – it transforms the car’s character, reduces weight, and unlocks significant horsepower with a proper tune. Whether you choose an OEM replacement for factory manners or an aftermarket system for aggressive sound and flow, the install process is straightforward with the right preparation and tools. Take your time with each step, use new gaskets, and torque everything to spec. Enjoy the new soundtrack, improved throttle response, and the pride of a job well done.