Upgrading to a turbo-back exhaust system is one of the most rewarding modifications for a Subaru WRX. It unlocks significant horsepower gains, improves turbo spool response, and gives the boxer engine a deeper, more aggressive note. The Borla 3-inch cat-back system, in particular, is a popular choice among enthusiasts for its stainless steel construction, S-Type sound technology, and straightforward installation. While a full turbo-back system (downpipe + cat-back) offers even more gains, this guide focuses on the cat-back portion — the section from the downpipe back — which is entirely DIY-friendly for the average owner with basic mechanical skills.

In this comprehensive walkthrough, we’ll cover every step needed to remove the factory exhaust and install the Borla 3-inch cat-back system on your WRX. We’ll also include torque specifications, alignment tips, and how to avoid common pitfalls. By the end, you’ll have a professional-grade installation that sounds great and performs even better.

Tools and Materials You'll Need

Having the right tools on hand before you start is essential. The Borla cat-back system includes the necessary hardware (clamps, bolts, and hangers), but you’ll still need standard shop tools. Below is a detailed list, including optional items that can make the job easier.

Required Tools

  • Jack and jack stands (or a lift) — Ensure the vehicle is safely supported. Use a floor jack and two rear jack stands at minimum.
  • Socket set — Metric sockets in 10mm, 12mm, 14mm, and 17mm are most common for exhaust bolts and hanger brackets.
  • Combination wrenches — Same sizes as sockets, helpful for tight spaces.
  • Torque wrench — Critical for tightening bolts to spec without stripping threads.
  • Rubber mallet — Used to loosen stubborn exhaust hangers or align pipes.
  • Exhaust hanger removal tool (or a set of pliers with a curved tip) — Makes pulling rubber hangers off studs much easier.
  • New exhaust gaskets — Even if the stock gasket “looks okay,” replace it to prevent leaks. Borla may include a gasket; if not, buy a 3-inch flat gasket for the downpipe-to-cat-back connection.
  • Penetrating oil (e.g., PB Blaster, WD-40 Specialist) — Spray on rusted nuts/bolts 30 minutes before removal.
  • Safety glasses and gloves — Exhaust systems accumulate dust, rust, and sharp edges.

Optional but Helpful

  • Brake cleaner or degreaser — Clean the downpipe flange before installing the new gasket.
  • Wire brush — Remove rust from the downpipe studs.
  • Anti-seize compound — Apply to the downpipe studs and clamp threads to ease future removal.
  • Second jack or exhaust support stand — Helps support the heavy Borla system during alignment.
  • OBDII scanner — To clear any check engine lights after reconnecting battery (not usually needed for a cat-back).

Preparation: Safety First, Then Setup

Before turning a single bolt, take these preparatory steps. Skipping them can lead to injury or damage to your car.

Park and Secure the Vehicle

  • Choose a level surface — Concrete floor is ideal. Avoid gravel or steep inclines.
  • Engage the parking brake — Pull it firmly. If working on an automatic, put it in Park; for manual, leave it in gear (or reverse).
  • Disconnect the battery — Remove the negative terminal first, then positive. This prevents electrical shorts and accidental airbag deployment. Wait at least 5 minutes before proceeding.
  • Raise the rear of the vehicle — Using the floor jack, lift from the rear subframe or differential crossmember. Do not lift from the exhaust pipes. Place jack stands under the rear pinch welds or subframe lift points. Lower the vehicle slowly onto the stands, then shake it to confirm stability.

Under-Vehicle Inspection

  • Spray penetrating oil on all exhaust bolts and hanger pins that will be removed. Pay special attention to the two bolts connecting the cat-back to the downpipe.
  • Inspect the existing exhaust for rust or damage. If the hangers are brittle, replace them now (they’re inexpensive).
  • Ensure you have enough clearance to slide the stock exhaust out from under the car. Remove any underbody panels or heat shields that might obstruct removal.

Removing the Stock Exhaust System

The factory exhaust on a WRX is relatively straightforward to remove. Work from the front (near the downpipe) to the back.

Step 1: Disconnect the Downpipe-to-Cat-Back Connection

  • Locate the flange where the downpipe meets the mid-pipe. This is near the front of the center tunnel, under the driver/passenger floor area.
  • Use a 14mm socket to remove the two bolts and nuts. If they’re tight, use a breaker bar. Do not discard these bolts — they will be reused with the Borla system.
  • If the gasket sticks, gently pry the flange apart with a flathead screwdriver (be careful not to damage the downpipe surface).
  • Once separated, pull the mid-pipe slightly downward to create slack.

Step 2: Remove Exhaust Hangers

  • The WRX uses several rubber hangers along the exhaust. Usually there are three or four: one near the mid-pipe, two on the muffler, and one on the rear resonator (if equipped).
  • Use the hanger removal tool to hook around the hanger pin and pull the rubber ring off. Alternatively, apply soapy water or silicone spray to the pin, then twist and pull with pliers. A rubber mallet tapped on the tool helps dislodge stubborn hangers.
  • Work from front to back as you go: first the mid-pipe hanger, then the muffler hangers.

Step 3: Slide Out the Stock Exhaust

  • With all hangers free and the downpipe disconnected, the exhaust should be able to slide out toward the rear of the car. You may need to jiggle it to clear the rear axle and differential.
  • Lower the exhaust gently. It’s heavy — ask a helper or use a second jack to support it. Once it’s clear, drag it out from under the car.
  • Set the old exhaust aside. You can sell it or keep it as a backup.

Pro tip: If a stud or bolt breaks during removal, don’t panic. Many WRX downpipe flanges are replaceable, but for cat-back installation, you only need the downpipe side intact. Damaged downpipe studs can be extracted or replaced depending on your downpipe design.

Installing the Borla 3-Inch Cat-Back System

Borla’s cat-back system is engineered for a precise fit. However, proper alignment takes patience. Follow these steps carefully to avoid rattles and exhaust leaks.

Step 1: Prepare the Downpipe Flange

  • Clean the downpipe flange with brake cleaner and a wire brush. Remove any old gasket material, rust, or debris.
  • Place the new gasket over the downpipe studs. Ensure it’s centered. Some downpipes use spring-loaded bolts; if yours does, you may need longer hardware (Borla includes hardware in the kit).

Step 2: Assemble the Borla System (If Not Pre-Assembled)

  • The Borla cat-back typically comes in three sections: the front pipe (connects to downpipe), a center section with a resonator (or straight pipe), and the rear muffler section with tips. Lay them out on the ground to confirm the orientation.
  • Do not fully tighten any clamps until the entire system is loosely hung. This allows you to adjust alignment.
  • Slide the clamps onto the pipes before connecting them — it’s a common mistake to forget a clamp and have to disassemble later.

Step 3: Hang the Front Section

  • From under the car, guide the front pipe up to the downpipe flange. Insert the two bolts (or studs) through the flange, hand-tighten the nuts (using the original bolts if they match the thread pitch). Borla sometimes includes new bolts; use them if provided.
  • Place the rubber hanger(s) into the bracket on the front section. Use a little dish soap to ease installation. Ensure the hanger is fully seated on the pin.
  • Do not fully tighten the downpipe bolts yet — only snug them to hold in place.

Step 4: Install Center and Rear Sections

  • Attach the center section (with resonator) to the front pipe using the supplied clamp. Slide the clamp over the joint and hand-tighten the nut.
  • Hang the center section using its rubber hanger.
  • Next, slide the rear muffler section onto the center section. Again, use a clamp and hand-tighten.
  • Insert the two rear hangers into the muffler brackets. The Borla muffler typically has two hanger positions; make sure both are engaged.
  • Check that the exhaust tips are roughly aligned with the rear bumper cutouts. They should be centered both vertically and horizontally.

Step 5: Align and Tighten

  • With everything loosely connected, go back and adjust the position of each section. The joints should have equal spacing around the pipe overlap (usually 1–2 inches).
  • Tighten the downpipe bolts to 35–40 ft-lbs (check your WRX service manual for exact spec). Use a torque wrench.
  • Tighten all band clamps to 40–50 ft-lbs or as specified by Borla. Over-tightening can crush the pipes; under-tightening leads to leaks.
  • Re-check exhaust tip alignment. If they’re off, loosen the clamps, twist the rear section slightly, and retighten.
  • Finally, verify each rubber hanger is fully seated and not partially pulled off.

Important: If you have an aftermarket downpipe (e.g., 3-inch with a different flange angle), you may need an adapter or different gasket. The Borla cat-back is designed for factory downpipes, but many 3-inch downpipes match the same flange pattern. Check fitment on the Borla official website for your specific WRX model year.

Final Adjustments and Checks

You’re almost done. Now it’s time to verify everything is secure and properly sealed.

Leak Check

  • With the car still on jack stands, reconnect the battery (negative last). Start the engine and let it idle.
  • Listen for hissing sounds near the joints — that indicates a leak. Also feel around the flanges with your hand (but do not touch hot surfaces after the engine runs for more than a minute).
  • A small soap-and-water solution sprayed on the joints will bubble if there’s a leak. Use this method for a definitive check.
  • If you hear a leak, shut off the engine, let it cool, and tighten the corresponding clamp or bolt.

Tip Alignment

  • The Borla tips should be parallel to the bumper cutout and not touching any trim. If they’re too far left or right, loosen the rear clamp and rotate the muffler can.
  • Vertical alignment can be adjusted by bending the hanger brackets slightly (use a screwdriver to pry gently) or by adding/removing washers at the hanger mount.
  • Once aligned, re-check the clamp torque.

Rattle Check

  • While the car is running, rev the engine gently (do not exceed 3000 rpm while on jack stands) and listen for any metal-on-metal contact. Common causes: exhaust hitting the sway bar, differential, or underbody braces.
  • If you hear rattling, identify the contact point and adjust the pipe position. In some cases, you may need to slightly bend a heat shield or add a small zip tie to hold wiring away.

Reconnecting the Battery and Lowering the Vehicle

  • Reconnect the positive terminal first, then negative. Ensure the connections are tight.
  • Start the engine and let it idle for 2–3 minutes. The ECU will relearn idle; it may hunt slightly for the first minute — that’s normal.
  • While the engine is running, do a final visual check underneath for any loose hangers or dripping water (condensation from the new exhaust is normal).
  • Using the floor jack, lift the vehicle slightly to remove the jack stands. Lower it in stages, shaking the car to ensure it’s stable.
  • Take the WRX for a short test drive (5–10 miles) on various roads. Listen for changes in sound and check for any new leaks once the system is heat-cycled.
  • After the drive, re-check the downpipe bolts and all clamps. They may need a slight re-torque.

Aftercare and Maintenance

Borla exhausts are made from T-304 stainless steel and are highly corrosion-resistant. However, a few habits will keep them looking and sounding great for years.

  • Break-in period: The sound will change slightly after 500–1000 miles as soot builds up inside the packing. Don’t be alarmed if the idle becomes deeper over time.
  • Clean the tips: Use a dedicated stainless steel cleaner or a mild soap-and-water mix. Avoid abrasive pads that can scratch the polished finish.
  • Check fasteners periodically: Every oil change, give the exhaust a quick visual inspection and re-torque the clamps if needed.
  • Watch for leaks: If you develop a leak at any joint, replace the gasket or tighten the clamp immediately. Even a small leak can cause drone and reduce performance.

Frequently Asked Questions

Will this void my warranty?

A cat-back exhaust is generally considered a “bolt-on” modification and does not void your entire warranty. However, if the exhaust causes damage (e.g., by overheating nearby components due to misalignment), the dealership may deny coverage for that specific repair. Always check with your dealer and keep receipts. For more information, see this overview of the Magnuson-Moss Warranty Act.

Do I need a tune for a cat-back exhaust?

No. A cat-back exhaust does not alter the engine’s AFR (air-fuel ratio) in a way that triggers a check engine light. The ECU can easily adapt to the minimal backpressure change. If you later install a downpipe (turbo-back), a tune becomes necessary.

How long does the installation take?

A first-timer should expect 2–3 hours, including preparation and clean-up. Experienced DIYers can do it in 45–90 minutes. The Borla system’s fitment is excellent, which speeds up the process.

Conclusion

Installing the Borla 3-inch cat-back exhaust on your WRX is a rewarding upgrade that delivers a noticeable improvement in sound and throttle response. By following this detailed guide — from proper safety setup and removal to careful alignment and final checks — you can achieve a leak-free, rattle-free installation that will last for years. The key is patience: never force a connection, always use new gaskets, and double-check your work with a cold and hot inspection. Enjoy the new soundtrack of your WRX, and happy wrenching.

For additional DIY resources, check out the IWSTI forum’s exhaust installation guides or the official Borla support page for torque specifications specific to your kit.