Why Upgrade to Greddy GT-R Downpipes?

The Nissan GT-R's twin-turbo V6 responds exceptionally well to exhaust modifications. The factory downpipes are restrictive, designed primarily for noise compliance and cost efficiency. Swapping to Greddy downpipes immediately reduces backpressure, allowing exhaust gases to exit the turbos more freely. This translates to faster turbo spool, increased horsepower (typically 30–50 whp on a stock or lightly tuned car), and a more aggressive exhaust note. Greddy's reputation for precision fitment and durable stainless steel construction makes them a preferred choice for GT-R owners who want reliable gains without fighting with ill-fitting parts.

Tools and Materials Needed

Before starting, assemble the following items to avoid interruptions:

  • Greddy GT-R downpipe set (3-inch or 4-inch, depending on model)
  • Metric socket set (10mm, 12mm, 14mm, 17mm)
  • Torque wrench (capable of 25–50 ft-lbs)
  • Ratchet with extension bars (6-inch and 12-inch)
  • Breaker bar for stubborn bolts
  • Floor jack and four jack stands
  • Safety glasses and mechanic gloves
  • Penetrating oil (e.g., WD-40 or PB Blaster)
  • Exhaust gasket sealant (high-temp copper or Permatex Ultra Copper)
  • New exhaust gaskets (Greddy typically includes them, but have spares)
  • Flathead screwdriver or trim tool (for hose clamps)
  • Work light or headlamp

Preparation and Safety

Park the GT-R on a level concrete surface. Allow the engine to cool completely – exhaust components retain heat for hours. Engage the parking brake and chock the rear wheels. Disconnect the negative battery terminal to prevent any accidental shorts. Lift the front of the vehicle using the jack, then place jack stands under the front subframe jacking points (not under the plastic undertray). Lower the car gently onto the stands, verifying stability before crawling underneath.

Step-by-Step Installation

1. Remove the Undertray

The factory plastic undertray covers the entire front underside. Use a 10mm socket to remove the push clips and bolts securing it. Set the undertray aside in a clean area. You will also need to remove the small metal heat shields near the catalytic converters if your GT-R is an early model (2009–2011). These shields are held by 12mm bolts and can be reused.

2. Access and Disconnect the Exhaust System

Start behind the front axle. The stock downpipes connect to the Y-pipe (or mid-pipe on later models). Use penetrating oil on the flange bolts and let it soak for a few minutes. Loosen the bolts connecting the downpipes to the exhaust system using a 14mm socket and extension. There are typically four bolts per flange. Once loosened, remove them completely and separate the flanges. You may need to pry gently with a flathead screwdriver to break the seal. Next, disconnect the exhaust hangers near the center muffler using a rubber-hanger removal tool or soapy water. This allows the rear exhaust section to drop slightly for extra clearance.

3. Remove the Factory Downpipes

The stock downpipes are bolted directly to the turbocharger outlet flanges. Access is tight: the upper bolts are best reached from above the engine, while the lower bolts are accessible underneath. Use a combination of short and long extensions. Apply penetrating oil to all turbo-to-downpipe bolts. Using a 12mm socket and a breaker bar, carefully break them loose. If a bolt feels seized, do not force it — apply more oil and wait. Removing the downpipes may require maneuvering them past the steering shaft and A/C lines. Twist and pull downward; lightly tap with a rubber mallet if stuck. Take note of any O2 sensor positions: you will transfer them to the Greddy downpipes later.

4. Prepare the Greddy Downpipes

Unbox the Greddy downpipes and inspect the flanges for any debris. Greddy typically provides new gaskets for both the turbo and exhaust connections. If not, order high-quality replacements from a Nissan dealer or aftermarket supplier. Transfer the factory O2 sensors from the old downpipes to the new ones. Use a 22mm O2 sensor socket and apply anti-seize compound to the threads. Pay attention to sensor orientation — the harness must not touch the downpipe body to avoid melting. Do not overtighten.

5. Install the Greddy Downpipes

Install the new gaskets on the turbo flanges. Hold the gasket in place with a dab of grease (prevents dropping). Lift the driver-side downpipe into position from underneath. Align the flange studs with the turbo holes. Hand-tighten the nuts first, then torque to 30–35 ft-lbs with a torque wrench. Repeat for the passenger side. Use a mirror or phone camera to verify none of the wiring harnesses are pinched. Reconnect the O2 sensors after the downpipes are bolted.

6. Reconnect the Exhaust

Slide the Y-pipe or mid-pipe flange onto the downpipe outlet. Install a new gasket between them (or reuse if still in good condition). Tighten the bolts to 35–40 ft-lbs. Reattach the exhaust hangers to their rubber mounts. Ensure there is even clearance all around the exhaust tunnel — the Greddy downpipes often fit tighter than stock, so check for contact with the chassis. If touching, loosen the flanges and reposition slightly.

7. Reinstall the Undertray and Heat Shields

Replace any heat shields you removed. Reinstall the undertray, securing it with all bolts and clips. Double-check that nothing is loose or hanging.

8. Lower the Vehicle and Perform a Leak Check

Jack the car slightly, remove jack stands, and lower to the ground. Reconnect the battery. Start the engine and let it idle. Listen for any exhaust hissing or ticking sounds around the flanges. Apply a soapy water mix to the joints — bubbles indicate a leak. If a leak is present, tighten the corresponding bolts slightly (1–2 ft-lbs increment). Do not exceed 40 ft-lbs on turbo flanges. Let the engine warm to operating temperature and inspect under the car for smoke or drips from the gaskets.

Post-Installation Tuning and Considerations

After installing Greddy downpipes, the GT-R will run richer in open loop due to reduced backpressure. The factory ECU can adapt to a degree, but for full power gains a tune is highly recommended. Many owners pair downpipes with an ECU reflash or a Cobb Accessport. Expect check engine lights if the rear O2 sensors are not disabled via tuning — Greddy downpipes delete the secondary catalytic converters on most models, triggering P0420/P0430 codes. A professional tuner can disable these codes and optimize fuel timing and boost targets. Additionally, consider upgrading the intake or intercooler to match the increased flow. Always follow local emissions regulations: Greddy downpipes are not legal for street use in some states (e.g., California) due to catalytic converter removal.

Expected Performance Gains

With a proper tune, a GT-R equipped with Greddy downpipes typically gains 40–60 wheel horsepower and 50–70 lb-ft of torque. Spool response improves noticeably — full boost arrives 300–500 RPM sooner. The exhaust note becomes deeper and more aggressive, with pronounced turbo whistle. Many owners report improved throttle response and a smoother powerband across the entire RPM range.

Maintenance and Long-Term Care

Greddy downpipes are built from T304 stainless steel and resist corrosion well. However, the constant heat cycles can loosen bolts over time. Re-torque all flange bolts after 500 miles. Inspect O2 sensor wiring for signs of chafing. If you drive in wet or salty conditions, occasional cleaning of the downpipe exterior with a mild degreaser prevents buildup. The flex sections (if equipped) should be inspected annually for cracks.

Conclusion

Installing Greddy GT-R downpipes is one of the most rewarding upgrades for the R35. The process is straightforward for a confident DIY mechanic but does require patience with turbo flange bolts. Following this expanded guide ensures a leak-free installation and maximum performance. For additional information, consult the official Greddy website, the GT-R Life forums, and BPM Tuning for ECU support. With the downpipes installed, your GT-R will deliver the performance and soundtrack Nissan intended.