Understanding Garrett GT-R Downpipes and Their Performance Impact

Upgrading to Garrett GT-R downpipes is one of the most effective bolt-on modifications for the Nissan GT-R (R35). These downpipes replace the restrictive factory units, which are heavily catalyzed and designed more for emissions compliance than performance. Garrett’s aftermarket downpipes feature mandrel-bent tubing, high-flow catalytic converters (or catless options), and larger diameter piping—typically 3 inches versus the stock 2.5-inch sections. This reduction in backpressure allows the twin-turbocharged VR38DETT engine to breathe more freely, resulting in gains of 30-50 wheel horsepower and similar torque increases on a stock vehicle, with even greater improvements when combined with a custom ECU tune.

The installation process is straightforward for a mechanically inclined beginner, but it does require attention to detail, proper tools, and a safe workspace. This expanded guide walks through each step—from preparation to post-installation testing—with expert tips to ensure a leak-free, trouble-free installation. Whether you choose Garrett’s catted or catless downpipes, following these instructions will help you unlock your GT-R’s true potential.

Tools and Materials Needed

Gathering the correct tools and supplies before starting saves time and prevents frustration. The Garrett GT-R downpipe kit typically includes new hardware (bolts, nuts, washers) and gaskets, but it’s wise to have backups on hand. Below is a complete list categorized by function.

Essential Tools

  • Socket and ratchet set – Metric sockets (10mm, 12mm, 14mm, 17mm) with extensions and a universal joint for tight spaces.
  • Wrench set – Combination wrenches (10mm to 19mm) for reaching awkward fasteners.
  • Torque wrench – A 3/8-inch drive torque wrench capable of 15-50 ft-lb is ideal for downpipe bolts.
  • Screwdriver set – Flathead and Phillips for releasing hose clamps or prying stubborn brackets.
  • Jack and jack stands – A low-profile jack and a pair of sturdy 3-ton jack stands are mandatory for safe lifting.
  • Safety equipment – Safety goggles, mechanic’s gloves, and long pants/sleeves to protect against sharp edges and hot components.

Consumables and Supplies

  • New gaskets – The Garrett kit includes turbo-to-downpipe and downpipe-to-exhaust gaskets. If reusing stock gaskets, replace them anyway – inexpensive insurance against leaks.
  • Anti-seize compound – Apply to all exhaust bolts to prevent seizure from high heat and corrosion.
  • Penetrating oil – Spray onto rusty nuts and studs the night before to ease removal.
  • O2 sensor socket – A 7/8-inch (22mm) oxygen sensor socket is needed if your GT-R uses wideband sensors that require careful removal.
  • Shop towels and pipe cleaners – For cleaning gasket mating surfaces.
  • Exhaust hanger removal tool – Optional but helpful for releasing the rubber hangers holding the mid-pipe.

Preparation: Creating a Safe and Organized Workspace

Before you touch a single bolt, take the time to prepare your GT-R and your environment. Working under a car is inherently dangerous, so follow these preparation steps meticulously.

Vehicle Positioning and Safety

  • Park on a flat, level surface. Concrete is ideal; avoid gravel or grass that can shift under the jack.
  • Engage the parking brake firmly. Chock the rear wheels with wheel chocks for added security.
  • Disconnect the negative battery terminal. This eliminates the risk of accidental electrical shorts, particularly near sensitive engine sensors.
  • Allow the exhaust system to cool completely. Even after a short drive, catalytic converters and turbochargers can exceed 400°F. Let the car sit overnight for best results.

Lifting the GT-R

The R35 GT-R has a reinforced aluminum chassis with designated jack points. Refer to your owner’s manual. Use the central front jack point to lift the front of the car, then place jack stands under the frame rail pinch welds. For downpipe work, you only need the front elevated enough to slide under safely (about 18 inches). Never rely solely on a hydraulic jack—always use jack stands rated for the vehicle’s weight (the GT-R weighs around 3,900 lbs).

Optional: Remove Engine Undercover

If your GT-R still has the factory under-tray, unbolt it (10mm bolts) to expose the downpipe area. This gives you clearer access to the turbo outlet flanges and O2 sensor wiring.

Removing the Old Downpipes

With the car safely lifted, you can begin removing the factory downpipes. The GT-R has left and right downpipes; work on one side at a time to avoid confusion with brackets and sensor routing.

Step 1 – Access and Visual Inspection

Look under the car to identify the downpipes. They run from the turbocharger outlet (just below the valve covers) down toward the catalytic converter and mid-pipe. The factory units have two oxygen sensors per side: primary wideband sensors near the turbo outlet and secondary narrowband sensors downstream. Note the routing of the sensor wiring harnesses – they often clip onto brackets attached to the downpipe.

Step 2 – Disconnect Oxygen Sensors

Use the O2 sensor socket to loosen each sensor from the downpipe. Unplug the electrical connectors from the main harness (located near the firewall on each side). Do not use excessive force; if a sensor is stubborn, spray penetrating oil and wait 10 minutes. Carefully thread the sensors out and set them aside in a clean area. Avoid contaminating the sensor tips with oil or dirt.

Step 3 – Unbolt the Downpipes from the Turbos

The downpipe flange connects to the turbo outlet with four bolts (12-14 mm). A universal joint and extension will help reach the lower bolts. Remove all four bolts and pull the downpipe away from the turbo. Some resistance is normal due to the gasket; gently pry the flange free with a flathead screwdriver, but watch not to damage the turbo outlet mating surface.

Step 4 – Disconnect the Mid-Pipe and Brackets

The lower end of each downpipe connects to the mid-pipe via a bolted flange (typically two bolts). There may also be a bracket holding the downpipe to the engine block. Remove those bolts and free the downpipe. If the rubber exhaust hangers prevent the mid-pipe from dropping, use an exhaust hanger tool or soapy water to slide them off.

Step 5 – Remove the Downpipes

Slide each downpipe out from below. You may need to tilt and turn it to clear the transmission bellhousing and subframe. If a pipe seems stuck, double-check that all sensors, brackets, and flange bolts are detached. Never force it—you risk bending the turbo outlet flange.

Installing the New Garrett GT-R Downpipes

Now the fun part: fitting the high-performance Garrett downpipes. Follow each step carefully to avoid cross-threading, gasket misalignment, or clearance issues.

Preparing the Mating Surfaces

Clean both the turbo outlet flange and the mid-pipe flange with a wire brush and brake cleaner. Remove any old gasket material or carbon deposits. A clean surface is crucial for a leak-proof seal. Apply a thin film of anti-seize to the studs or bolt threads (not the gasket face).

Gasket Placement

Garrett provides high-quality multi-layer steel (MLS) or graphite gaskets. Place the new gasket onto the turbo outlet studs. Do not use any gasket sealant unless specified—dry gaskets work best with metal flanges. For the downpipe-to-mid-pipe joint, use the supplied gasket as well.

Positioning and Bolting the Downpipe

Slide the new downpipe into place from below. Align the upper flange onto the turbo studs, then the lower flange onto the mid-pipe studs. Hand-tighten all bolts to hold the pipe in place. Check clearance around the transmission, steering shaft, and frame rails—Garrett downpipes are designed to fit, but occasionally a heat shield may need minor adjustment. Once satisfied, torque the turbo-to-downpipe bolts to the factory specification: typically 25-30 ft-lb. Use a crisscross pattern. Then torque the mid-pipe bolts to 30-35 ft-lb. Do not overtighten, as turbo studs can snap.

Reconnecting Sensors and Brackets

  • Reinstall the O2 sensors into their original ports on the new downpipes. Apply anti-seize to the sensor threads (a tiny amount—avoid the tip). Torque to 25-30 ft-lb.
  • Plug the electrical connectors back into the harness. Verify the clips click securely.
  • Reattach any support brackets removed earlier. Some aftermarket downpipes use a flexible bracket to reduce stress; use the supplied hardware.

Repeat for the Other Side

If you have a pair (all GT-Rs have two downpipes), install the second unit following the same process. Take your time; rushing leads to mistakes.

Final Checks and Reassembly

Before lowering the car, complete these critical inspections.

Visual Inspection

  • Ensure all bolts are tight and properly torqued. Wiggle each downpipe by hand to confirm it’s secure.
  • Check that sensor wires are not pinched, melted by the downpipe heat, or in contact with the exhaust.
  • Verify there are no tools, rags, or debris left under the hood or near the exhaust.

Apply Anti-Seize to Exposed Bolts

If you missed it earlier, dab anti-seize onto the exposed threads of the bolts you might need to touch later (O2 sensors, flanges). This prevents corrosion for future removal.

Lower the Vehicle

Remove the jack stands carefully, lower the car, then reinstall the engine undercover if you removed it. Reconnect the negative battery terminal.

Testing Your Installation

A proper test ensures you didn’t create leaks or damage nearby components. Follow this procedure:

  1. Cold start and idle – Start the engine from cold. Listen for any hissing or ticking sounds from the exhaust joints. A small leak will often create a distinct “tick-tick-tick” that increases with revs. If you hear anything suspicious, shut off the engine and tighten the flanges slightly (do not exceed torque spec).
  2. Check for exhaust leaks – While the car idles, slide a glove or shop towel near each flange (be careful of hot surfaces). You can also use a handheld smoke machine or a spray bottle with soapy water to look for bubbles at the joints. Even a minor leak will reduce power and cause drone.
  3. Visual check for heat clearance – After running at idle for 2-3 minutes, the pipes will warm. Look underneath to ensure the downpipes are not contacting the chassis, wiring, or brake lines. The GT-R downpipe area is tight; rubbing can melt wires or create vibration.
  4. Test drive – Take the car for a 10-15 minute drive on varied roads. Listen for rattles, check for unusual odors (burning off factory oils is normal initially). Accelerate gently at first, then perform a few moderate pulls. The car should feel quicker and the exhaust note will be deeper. If you have a boost gauge, spool may occur 200-300 RPM earlier.
  5. Check engine light (CEL) consideration – If you installed catless downpipes, a CEL for catalyst efficiency is highly likely. You’ll need a custom tune, ECU flash, or O2 sensor spacers to eliminate the code. Garrett’s catted downpipes use high-flow catalysts that often avoid CELs on stock tuned cars, but results vary. Always plan for a tune to maximize gains and driveability.

Performance Benefits and Tuning Considerations

Garrett GT-R downpipes are not just a sound upgrade; they significantly improve the VR38DETT’s efficiency. The larger diameter and smoother mandrel bends reduce exhaust backpressure, allowing the turbos to spool faster and hold boost longer. Typical dyno results with catted Garrett downpipes on a stock vehicle show 30-40 whp and 40-50 wtq gains. With a proper ECU tune (e.g., from Cobb Tuning or a local shop specializing in GT-Rs), those numbers can climb to 60-80 whp.

However, the stock ECU’s fuel and timing maps are calibrated for the restrictive factory exhaust. Adding downpipes without a tune will still yield some improvement, but the engine may run lean at high load, limiting power and risking knock. For beginners, we recommend pairing downpipe installation with a reputable off-the-shelf (OTS) tune from companies like Cobb or Ecutek. The investment is modest compared to the power unlocked.

For more technical details on Garrett’s downpipe design and materials, visit their official product page: Garrett Motion – GT-R Downpipes. Additionally, the GT-R Heritage forum offers community-driven installation tips and dyno results that can help you choose between catted and catless options.

Common Beginner Mistakes to Avoid

  • Forgetting to disconnect the battery – Sparks near the fuel system or O2 sensor wiring are dangerous. Always disconnect.
  • Using old gaskets – Even if they look okay, MLS gaskets lose their sealing ability after compression. Replace them.
  • Over-tightening bolts – Turbo studs are brittle. Stick to torque specs. A broken stud requires drilling and extraction—not fun.
  • Neglecting to lubricate O2 sensor threads – They’ll seize in the new downpipe, making future removal a nightmare.
  • Skipping the test drive – A small leak might only appear under load. Always verify after a hard run.

Conclusion

Installing Garrett GT-R downpipes is a rewarding weekend project that delivers tangible performance gains and a more aggressive exhaust note. With the right tools, a methodical approach, and attention to safety, even a first-time DIYer can complete the job successfully. The key is patience—don’t rush through the removal of stubborn factory bolts, and double-check every connection before starting the engine.

Once the downpipes are in and tested, consider complementary upgrades like a high-flow intake, intercooler, and a professional tune to fully exploit the engine’s breathing improvements. Your GT-R will thank you with sharper throttle response, faster spool, and exhilarating acceleration. As always, consult your vehicle’s service manual for any model-specific variations, and enjoy the process of making your R35 truly your own.