Why Replace the Stock Up-Pipe on Your Subaru Legacy GT?

The up-pipe on a turbocharged Subaru Legacy GT (2005‑2009) is a critical component that carries exhaust gas from the cylinder heads to the turbocharger. While the factory up-pipe on these models does not contain a catalytic converter (unlike some earlier WRX variants), it is still restrictive due to its narrow inner diameter, sharp bends, and cast iron construction. This restriction increases backpressure, slows turbo spool, and limits peak boost potential. Swapping to a Grimmspeed up-pipe — a mandrel-bent, smooth-flowing stainless steel unit — removes those bottlenecks. The result is quicker spool, higher ultimate boost, and a measurable power gain especially when combined with a tune.

Beyond raw numbers, the improved exhaust flow also lowers exhaust gas temperatures (EGTs) before the turbine, which can help protect the turbocharger during sustained high-load operation. For enthusiasts running a stage 2 setup or a larger turbo, the Grimmspeed up-pipe is a foundational upgrade that unlocks the full potential of other modifications. In this guide we will cover every step of the installation, from tool selection through final leak testing, so you can perform this swap safely and correctly.

Tools and Materials You Will Need

Before lifting the Legacy GT, gather all necessary items. Having everything on hand prevents unnecessary trips to the toolbox and reduces installation time.

Parts and Hardware

  • Grimmspeed up-pipe (PN: 132040 or 132041 for the Legacy GT; verify fitment)
  • New up-pipe-to-turbo gasket (often included with Grimmspeed, but buy a genuine Subaru or OEM-grade replacement as backup)
  • New up-pipe-to-exhaust manifold gaskets (two required; copper or multi-layer steel recommended)
  • Turbo-to-downpipe gasket (if you disturb the downpipe connection)
  • Anti-seize compound (for exhaust bolts to prevent galling)
  • Thread-locker (medium-strength) for small bolts that see vibration
  • Penetrating oil (like PB Blaster or Kroil) to free stubborn fasteners
  • Heat wrap or ceramic coating (optional, to reduce under‑hood temperatures)

Tools

  • Socket set (metric): 10mm, 12mm, 14mm, 17mm, 19mm deep and standard
  • Combination wrench set (10mm–19mm)
  • Torque wrench (capable of 20–40 ft‑lb range)
  • Ratchet with extensions (3″, 6″, 12″)
  • Breaker bar (for stubborn bolts)
  • Jack and jack stands or a lift
  • Flathead screwdriver and pick set (for prying stubborn gaskets)
  • Wire brush (for cleaning flange surfaces)
  • Safety glasses and mechanic’s gloves
  • Shop vacuum (to remove any debris that falls into open turbo inlet)

Preparing the Vehicle

Park the Subaru on a level concrete surface. Disconnect the negative battery terminal to eliminate any risk of shorting tools against the battery or triggering a check‑engine light during electrical disconnections. Allow the engine to cool completely — working on a hot exhaust system is dangerous and can cause burns.

Raise the front of the car using a jack and secure it on jack stands placed under the factory lift points. For additional working clearance, consider also raising the driver’s side slightly (the up‑pipe lives on the left side of the engine bay). Remove the plastic under‑tray that shields the engine bay below the front bumper.

Access to the up‑pipe from above is very tight on the Legacy GT. Most installers find it easier to remove the factory top‑mount intercooler (TMIC). This opens up the area around the turbo and firewall, allowing you to reach the up‑pipe fasteners more easily. To remove the intercooler:

  • Unclip the four intercooler‑to‑turbo Y‑pipe hoses (both sides).
  • Disconnect the boost control solenoid hoses attached to the intercooler.
  • Remove the two 12mm bolts securing the intercooler to the mounting brackets.
  • Carefully lift the intercooler and set it aside on a clean cloth. Plug the turbo inlet with a lint‑free rag to prevent debris from entering the engine.

Removing the Stock Up‑Pipe

The factory up‑pipe is sandwiched between the exhaust manifold and the turbocharger. Its removal is the most time‑consuming part of the job due to limited clearance and heat‑rusted fasteners.

Step 1: Access and Penetrating Oil

From above, spray the two bolts connecting the up‑pipe to the turbo and the two bolts at the exhaust manifold flange with penetrating oil. Let it soak for at least 15 minutes. While it works, remove any heat shields that block access. On the Legacy GT, this typically means removing the turbo heat shield (a two‑piece shield held by 10mm and 12mm bolts).

Step 2: Disconnect Supporting Components

  • Oxygen sensor: The factory up‑pipe on some Legacy GTs includes a small O₂ sensor port near the turbo flange. Disconnect the sensor harness and carefully unscrew it from the up‑pipe. (On later models this sensor may be in the downpipe; verify before proceeding.)
  • Turbo inlet hose: Loosen the clamp at the turbo compressor inlet and pull the silicone hose off. This provides a bit more wiggle room to reach the up‑pipe bolt on top of the turbo.
  • Dipstick tube bracket: The up‑pipe often shares a bracket with the engine dipstick. Unbolt the bracket using a 12mm socket and move the dipstick out of the way.

Step 3: Unbolt the Up‑Pipe

Using a 14mm socket with an extension, reach the two nuts that secure the up‑pipe to the turbo flange (located on top of the turbine housing). These are often stubborn — use a breaker bar if needed. Then move underneath the car and remove the two 14mm nuts or bolts that attach the up‑pipe to the exhaust manifold flange (located behind the left front wheel well). Once all four fasteners are loose, the up‑pipe should be free. If it sticks, gently tap it with a rubber mallet from above. Do not pry against the turbo or manifold flanges to avoid warping them.

Slide the stock up‑pipe out through the gap between the engine and the firewall. On the Legacy GT, it may need to be rotated slightly to clear the block. Inspect the removed pipe: note the narrow diameter (typically 1.5″ ID) and any cast obstruction that hindered flow.

Preparing the Flanges

Before installing the Grimmspeed up‑pipe, clean all sealing surfaces thoroughly. Use a wire brush or a razor blade to scrape off old gasket material and carbon deposits from both the exhaust manifold flange and the turbo inlet flange. Wipe the surfaces with a shop towel and brake cleaner to remove oil residue. Check for flange warpage with a straightedge — if either flange is bent, the new gaskets may not seal, causing a persistent exhaust leak.

Installing the Grimmspeed Up‑Pipes

Grimmspeed up‑pipes are precision‑made with smooth mandrel bends and typically feature a flex section to reduce stress on the turbo and manifold. The installation is essentially the reverse of removal, but with attention to proper gasket placement and torque sequence.

Step 1: Install New Gaskets and Position the Up‑Pipe

Apply a thin smear of anti‑seize to the threads of the bolts and studs that will be reused. Place the new gaskets over the studs on the exhaust manifold flange. Then, from underneath the car, guide the new up‑pipe into position. It should align easily if the flange surfaces are clean. Lift the pipe and slide the top flange onto the turbo studs. Do not force the pipe — if alignment is off, loosen the turbo mounting bolts slightly to re‑center the turbo (but this is rarely necessary for a direct‑fit Grimmspeed unit). Insert the bolts and hand‑tighten them.

Step 2: Torque All Fasteners

Use a torque wrench with the appropriate socket. Grimmspeed recommends tightening all up‑pipe bolts to 35 ft‑lb (47 N·m) for M8‑sized hardware and 25 ft‑lb (34 N·m) for M10 studs. Always tighten in a cross‑pattern where possible. Start with the two bolts at the turbo flange, then the two at the exhaust manifold flange. Re‑torque after the first heat cycle.

Step 3: Reconnect the Oxygen Sensor (if applicable)

If your factory up‑pipe had a sensor, the Grimmspeed pipe will include a bung for it. Apply anti‑seize to the sensor threads and tighten it to 35 ft‑lb. Reconnect the harness and secure the wire with a zip tie away from the exhaust.

Step 4: Reinstall the Dipstick Bracket and Heat Shields

Bolt the dipstick bracket back onto the up‑pipe. Reinstall the turbo heat shield(s) using the original fasteners. Ensure no wires or hoses are pinched between the shield and the up‑pipe.

Reassembly and Final Checks

Now that the up‑pipe is in place, reassemble the remaining components in reverse order of disassembly.

  • Reinstall the turbo inlet hose and tighten the clamp.
  • Reinstall the intercooler: ensure the Y‑pipe hoses are seated securely and all four clamp bolts are snug.
  • Reconnect the boost control solenoid hoses to the intercooler.
  • Reinstall the under‑tray and lower the vehicle.
  • Reconnect the battery negative terminal.

Leak Testing

Start the engine and let it idle. Listen for any hissing or ticking sounds from the up‑pipe flanges — that indicates an exhaust leak. A leak at the up‑pipe will cause a boost leak and can lean out the air‑fuel mixture, potentially damaging the engine. If you suspect a leak, use a shop vac in reverse (blowing) or a dedicated smoke machine to pressurize the system. Tightening the flange bolts slightly (if they are below spec) may resolve minor leaks. Do not overtighten, as this can strip threads or warp flanges.

Inspect the oxygen sensor wires and ensure they are not contacting the exhaust. Check for any loose hardware under the hood.

Test Drive

Take the Legacy GT for a cautious test drive. Under light throttle the car should feel normal; under moderate to heavy acceleration you should notice a quicker spool and stronger mid‑range pull. Watch the boost gauge (if you have one) — the Grimmspeed up‑pipe typically raises peak boost by 1–2 psi on an otherwise stock car. If the car goes into limp mode or throws a check‑engine light, scan for codes (a P0037 or P0139 can indicate a sensor issue, not a problem with the pipe itself).

Tuning and Expectations

While the Grimmspeed up‑pipe can be installed on a stock ECU, the greatest gains come when paired with a professional tune (via OpenSource or an Accessport). The reduced backpressure allows the turbo to flow more air, and the ECU needs to be calibrated to take advantage of the increased mass airflow. Expect power gains of 10–20 wheel horsepower with a tune, plus improved throttle response. Without a tune, you may see a small boost increase and slightly earlier spool, but the ECU’s fuel and ignition maps may not be optimized for the larger airflow.

Be aware that aftermarket up‑pipes are often louder than stock. The exhaust note becomes slightly more aggressive, especially under boost. This is normal and indicates better flow.

Common Mistakes and How to Avoid Them

  • Reusing old gaskets: Always replace all gaskets that are disturbed. A reused gasket will likely leak, causing boost loss and a ticking sound.
  • Over‑tightening bolts: Subaru studs are strong but can fatigue. Tighten to spec and no more.
  • Forgetting to oil the turbo flange studs: Anti‑seize prevents the nuts from galling on the studs — a common cause of broken studs during removal.
  • Neglecting to plug the turbo inlet: Any debris that falls into the turbo while the up‑pipe is off can destroy the compressor wheel on startup.
  • Ignoring heat shielding: The up‑pipe radiates massive heat. The factory heat shields are not optional — reinstall them to protect nearby wiring and the brake master cylinder.

Additional Resources

For more detailed discussion of Subaru up‑pipe upgrades and Legacy‑specific tips, refer to these community resources:

Conclusion

Installing a Grimmspeed up‑pipe on your Subaru Legacy GT is one of the most rewarding bolt‑on modifications you can perform. It directly attacks the biggest restriction in the factory exhaust tract, resulting in faster spool, higher peak boost, and a genuine increase in horsepower. By following the steps outlined above — from thorough preparation and careful removal to precise torque specs and leak checking — you can complete this project in a weekend and enjoy a noticeably more responsive and powerful Legacy GT. For maximum benefit, pair the up‑pipe with a proper engine tune and a quality cat‑back or downpipe. Your turbo will thank you.