Why Upgrade to a Perrin Turbo Downpipe?

Your Subaru WRX is a performance machine, and one of the most effective bolt‑on modifications you can make is replacing the restrictive factory downpipe with a high‑flow aftermarket unit like the Perrin Turbo Downpipe. This single component can unlock significant horsepower and torque gains, sharpen throttle response, and give your exhaust note a deeper, more aggressive tone. Whether you’re chasing better spool times or just want your WRX to sound the way it always should have, a Perrin downpipe is a proven upgrade.

This step‑by‑step guide walks you through the entire installation process, from gathering the right tools to performing the final test drive. We’ll cover safety precautions, torque specifications, and common pitfalls to help you complete the job with confidence. If you’re installing a catted version, you’ll retain emissions legality in most areas; a catless downpipe offers maximum performance but may require an aftermarket tune and is not street‑legal in some jurisdictions.

Tools and Materials

Having everything ready before you start keeps the job moving smoothly and reduces frustration. Below is a comprehensive list of what you’ll need.

  • Perrin Turbo Downpipe with included hardware and gaskets
  • Socket set – metric sockets (10mm, 12mm, 14mm, 17mm, 19mm)
  • Torque wrench (½‑inch drive, capable of 30–80 ft‑lb)
  • Jack and two jack stands (rated for at least 3 tons)
  • PB Blaster or penetrating oil – essential for rusted bolts
  • Safety glasses and gloves
  • 6‑inch extension and a universal joint for tight spaces
  • Flathead screwdriver or trim removal tool (for exhaust hangers)
  • Oxygen sensor socket (22mm) if reusing stock sensors
  • Anti‑seize compound for bolt threads and O2 sensor threads
  • Wire brush to clean flange surfaces
  • Shop rags and a drain pan (a small amount of oil may drip)

Optional but recommended: a set of new OEM exhaust gaskets, a flex‑head ratchet, and a floor jack with a rubber pad to protect the pinch weld.

Preparation

Before you crawl under the car, take a few minutes to prepare your workspace and vehicle. A clean, well‑lit garage with a flat concrete floor is ideal.

Cool Down the Exhaust

Let the engine cool completely – at least two hours after the last drive. Hot exhaust components cause severe burns and can make bolts harder to remove as they expand.

Lift and Secure the Vehicle

Use a floor jack to raise the front of the WRX. Place jack stands under the front subframe jack points (the reinforced sections just behind the front wheels). Never rely on a jack alone. Give the car a gentle shake to confirm it’s stable before getting underneath.

For extra working room, you may also lift the rear slightly and place stands under the rear jack points. Ensure the parking brake is engaged and chock the rear wheels.

Disconnect the Battery (Optional but Smart)

Disconnecting the negative battery terminal prevents accidental short circuits if you’re working near electrical connectors, and it also resets the ECU, which some Subaru owners prefer after exhaust modifications.

Removing the Stock Downpipe

The factory downpipe is heavy, restrictive, and often stubborn. Patience and penetrating oil are your friends.

Spray All Bolts with Penetrating Oil

Apply PB Blaster to every nut and bolt you’ll remove: the turbo‑to‑downpipe flange bolts (two studs or nuts), the downpipe‑to‑midpipe flange (two bolts), the two O2 sensor locations, and any bracket bolts. Let it soak for 10–15 minutes while you prepare the car.

Remove the Oxygen Sensors

Using an O2 sensor socket or a 22mm wrench, carefully loosen the front O2 sensor (located before the turbo, but the downpipe connects after the turbo). The rear sensor is on the downpipe itself – unplug its electrical connector first, then remove the sensor. Apply anti‑seize to the threads of both sensors before reinstalling later.

Tip: Mark the sensors with tape so you don’t confuse which one goes where (though they are usually keyed differently).

Unbolt the Downpipe from the Turbo

Access the two or three fasteners holding the downpipe to the turbo outlet. On most WRX models, these are studs with nuts. Use a combination of a socket, extension, and universal joint to reach them. If they’re extremely tight, a breaker bar works well. Remove the nuts and set them aside.

Separate the Downpipe from the Midpipe

Locate the slip‑joint or flange connection between the downpipe and the center exhaust section. Remove the two bolts. If the exhaust system uses a spring‑loaded joint, be aware that the springs will pull the flanges together – Compress the springs or carefully pry the flanges apart once the bolts are out.

Remove Exhaust Hangers

There may be one or two rubber exhaust hangers holding the downpipe to the car body. Use a flathead screwdriver or hanger removal tool to pop the metal prongs out of the rubber isolators. It helps to lubricate the rubber with a little soapy water.

Lower and Remove the Stock Downpipe

With everything disconnected, carefully wiggle the downpipe out from the engine bay. It can be tight – you may need to rotate it and guide it past the steering rack and subframe. If it sticks, check for any remaining bolts or hangers. The stock unit is heavy, so support it with your free hand.

Safety note: There’s a small chance loose carbon deposits will fall from the pipe – wear safety glasses and a dust mask if you’re sensitive to exhaust particulates.

Installing the Perrin Turbo Downpipe

Now for the exciting part. The Perrin downpipe is engineered for a direct fit, but following these steps ensures a perfect seal and long‑term reliability.

Transfer the Oxygen Sensors

If you’re reusing the stock sensors, install them into the Perrin downpipe’s bungs. Use anti‑seize on the threads, and tighten them to roughly 30 ft‑lb. Position the wire routing so it doesn’t touch the downpipe or nearby heat sources.

Inspect and Clean Flange Surfaces

Use a wire brush or scotch‑brite pad to clean the turbo outlet flange and the midpipe flange. Any old gasket material, rust, or debris will cause leaks. Wipe the surfaces with a clean rag.

Apply New Gaskets

Use the gaskets included with your Perrin downpipe, or purchase OEM replacements. Perrin often supplies a thick multi‑layer steel (MLS) gasket – do not use sealant. Place the gasket on the turbo flange, aligning the holes.

Position the Perrin Downpipe

Carefully maneuver the downpipe into place. It’s lighter than the stock unit and should slide in without major resistance. Align the downpipe flange with the turbo outlet studs and push it into position. If the midpipe connection is a flange, loosely install two bolts to hold it in place.

Hand‑Tighten All Fasteners

Start the nuts on the turbo studs – hand tighten them to ensure the downpipe is seated flush. Then install the two bolts at the midpipe connection. Do not fully tighten yet; you want the downpipe to “float” so you can adjust alignment.

Tighten to Torque Specifications

Use your torque wrench on all fasteners in a staggered sequence to avoid warping flanges. Standard torque for the turbo‑to‑downpipe nuts is 32–38 ft‑lb. For the downpipe‑to‑midpipe bolts, 30–35 ft‑lb is common. Always refer to the manufacturer’s instructions – some Perrin downpipes specify different values.

Important: Over‑tightening can strip threads or crush gaskets. Under‑tightening causes exhaust leaks and the dreaded “exhaust tick.”

Reattach Exhaust Hangers

Snap the downpipe’s hangers (if any) into the rubber isolators. You may need to apply a little force. If the midpipe connection uses a spring‑loaded system, install the springs and ensure they are seated properly.

Reconnecting Exhaust Components

Double‑check every connection before lowering the car. This is also a good time to inspect other exhaust sections for wear.

Check Clearance

Rotate the steering wheel lock‑to‑lock and check that the downpipe doesn’t contact the frame, steering rack, or any heat shields. A misaligned downpipe can rattle or cause damage. If clearance is tight, loosen and reposition the downpipe slightly.

Plug in O2 Sensor Connectors

Route the sensor wires away from hot surfaces and sharp edges. Secure them with zip ties if necessary. Connect the electrical plugs until they click.

Inspect Exhaust Mounts

Make sure all rubber hangers are properly engaged and not stretched to the point of failure. A sagging exhaust will rattle and make noise.

Final Checks and Test Drive

With everything tightened and connected, you’re ready to fire it up.

Leak Test

Start the engine and let it idle. While the car is still on stands, listen for any whistling, hissing, or popping around the downpipe flanges. Use a glove to carefully feel for air leaks – but be extremely cautious of hot surfaces. A shop towel can also be held near flanges to detect puffs of exhaust. If you hear a leak, shut off the engine, allow it to cool, and retighten the offending bolts.

Lower the Vehicle

Once you’re satisfied there are no leaks, turn off the engine, raise the car enough to remove the jack stands, and lower it to the ground.

Road Test

Take the WRX for a gentle drive for the first five minutes to let the system heat‑cycle. Gradually increase throttle to feel the performance gain – you’ll notice quicker spool and a more urgent pull. Listen for any new rattles, vibrations, or scraping sounds. After the drive, let the car cool and re‑check the downpipe bolts; they sometimes loosen slightly after the first heat cycle.

Post‑Installation Considerations

Engine Tuning

If you installed a catless downpipe, an aftermarket tune (e.g., Cobb Accessport or Open Source tune) is mandatory. Without a tune, the ECU will run rich, potentially causing boost spikes, knock, or catalytic converter failure. Even with a catted downpipe, a tune is highly recommended to fully utilize the increased flow and to optimize the air‑fuel ratio.

Emissions and Inspection

In many jurisdictions, removing or replacing the catalytic converter violates emissions laws. Retain the stock downpipe for annual inspections if needed. Perrin offers catted versions that are legal in many areas – check your local regulations.

Common Issues and How to Avoid Them

  • Stuck bolts: Soak in penetrating oil overnight if needed. Use a breaker bar and impact driver for extra stubborn nuts. Replace studs if they snap.
  • Exhaust leak at turbo flange: Often caused by a damaged gasket or dirty surface. Use only new gaskets and clean flanges perfectly.
  • O2 sensor wire burn: Route wires away from the downpipe. Use heat‑resistant wire loom if necessary.
  • No check engine light? If you install a high‑flow cat, you may still trigger a CEL for catalyst efficiency. An O2 sensor spacer (defouler) or a tune can eliminate this.

Conclusion

Installing a Perrin Turbo Downpipe is a satisfying DIY project that delivers real‑world performance improvements. By following this detailed guide, you’ve upgraded your WRX with a high‑quality component that enhances both power and sound. Remember to respect torque specifications, use generous penetrant, and always tune your engine after a significant exhaust mod. With proper installation, your Perrin downpipe will provide years of reliable, spirited driving.

For more information on the product, visit the Perrin Performance Official Website. Community forums like NASIOC offer additional tips and owner experiences. Always consult your vehicle’s service manual for model‑specific torque values and procedures.