Introduction

Upgrading to GTM GT-R downpipes is one of the most effective bolt-on performance modifications for the Nissan GT-R. By replacing the restrictive factory units, these downpipes reduce backpressure, improve turbo spool response, and unlock substantial horsepower and torque gains. Whether you own a CBA, DBA, or EBA model, installing GTM downpipes can transform the driving experience with sharper throttle response and a more aggressive exhaust note. This comprehensive guide provides a detailed, step-by-step installation procedure to help you complete the job safely and correctly, achieving maximum performance and reliability.

Why Upgrade to GTM GT-R Downpipes?

GTM downpipes are precision-crafted from high-quality stainless steel or Inconel, offering superior heat resistance and durability compared to stock components. The primary benefits include:

  • Reduced exhaust backpressure: Smoother exhaust flow allows the twin turbos to spool faster, reducing lag and improving throttle response.
  • Increased horsepower and torque: Gains of 30–50 whp are common on stock turbos, with even larger gains on upgraded turbos after tuning.
  • Enhanced exhaust note: A deeper, more aggressive tone without being overly loud, especially when paired with a cat-back system.
  • Improved heat management: Material choices like Inconel or ceramic-coated stainless steel lower under-hood temperatures, protecting nearby components.
  • Better flow for future upgrades: If you plan to upgrade turbos or add larger injectors, GTM downpipes provide the airflow capacity needed for higher power levels.

Understanding Downpipe Types

Catless vs. High-Flow Catted

GTM offers both catless and high-flow catted downpipes. Catless downpipes eliminate the catalytic converters entirely, maximizing flow but requiring a tune to avoid check engine lights and likely failing emissions tests in most areas. High-flow catted downpipes use a metallic substrate catalyst that flows significantly better than the restrictive factory cats while still passing visual inspections in many regions. Choose based on your local laws, emissions requirements, and willingness to tune the ECU.

Construction Materials

Stainless steel (304 or 321) is most common, offering excellent corrosion resistance and longevity. Inconel downpipes are lighter and handle extreme heat better, but cost more. Ceramic coating further reduces radiant heat. GTM downpipes are available in both materials; select based on budget and performance goals.

Tools and Materials Needed

Having the correct tools on hand before starting will save time and frustration. Below is a comprehensive list:

  • GTM GT-R downpipes (with included gaskets if any)
  • New exhaust gaskets (manifold to downpipe, downpipe to mid-pipe)
  • Socket set: 10mm, 12mm, 14mm, 17mm, 19mm sockets
  • Ratchet with extensions (3-inch, 6-inch, 12-inch)
  • Torque wrench (range 10–80 ft-lb)
  • Swivel or universal joint sockets for tight spaces
  • Jack and jack stands (or a lift)
  • Penetrating oil (e.g., WD-40 or PB Blaster)
  • Anti-seize compound (for fasteners)
  • Exhaust sealant or high-temp RTV (optional but recommended)
  • Safety goggles and mechanic gloves
  • O2 sensor socket (22mm) – if removing O2 sensors
  • Flathead screwdriver (for hose clamps or connectors)
  • Shop rags or towels
  • Flashlight or work light

Preparation and Safety

Park the vehicle on a level, solid surface. Engage the parking brake and chock the rear wheels. Allow the exhaust system to cool completely — touching a hot exhaust can cause severe burns. Disconnect the negative battery terminal if you will be working near any electrical connectors or sensors. Wear safety goggles to protect your eyes from falling debris or chemicals. Work in a well-ventilated area, especially if you plan to run the engine during leak checks.

Step-by-Step Installation

1. Lifting the Vehicle

Using a jack, lift the front of the GT-R high enough to gain comfortable access underneath. Place jack stands under the designated lift points (frame rails or subframe). Never rely solely on a jack. Verify the vehicle is stable before crawling underneath.

2. Removing the Stock Downpipes

Start by spraying penetrating oil on all exhaust fasteners — especially the bolts connecting the downpipes to the manifolds and the catalytic converters. Allow the oil to soak for 10–15 minutes. Remove any heat shields if present (typically held by 10mm or 12mm bolts). Carefully unbolt the stock downpipes from the exhaust manifolds and the mid-pipe. You may need to swivel the downpipe to clear the turbo outlets. Be mindful of O2 sensors; unplug them from the harness before fully removing the downpipe. In some cases, removing the O2 sensors with a special socket makes the job easier. Keep the stock hardware if you plan to reuse it, but new bolts and gaskets are recommended.

3. Installing the GTM GT-R Downpipes

Before installing, inspect the new downpipes for any damage and apply a thin layer of anti-seize to the O2 sensor threads if you are reinstalling them. If your downpipes have O2 bungs, ensure the sensor ports are clean. Insert the new gaskets between the downpipe and exhaust manifold. Align the downpipe with the manifold studs and carefully push it into place. It may require slight twisting to fit past the subframe. Hand-tighten the nuts first. Next, connect the lower end of the downpipe to the mid-pipe (or catalytic converter) using the provided gasket and bolts. Ensure the flanges mate squarely. Use exhaust sealant on the gasket surfaces for added leak protection.

4. Torquing Fasteners to Specification

Using a torque wrench, tighten all bolts and nuts to the manufacturer's specifications. Typically, manifold-to-downpipe nuts should be torqued to approximately 30–35 ft-lb. The mid-pipe connection may be similar. Do not overtighten, as this can strip threads or warp flanges. If you don't have the exact specs from GTM, consult the factory service manual for the GT-R — many aftermarket downpipes use the same torque values as stock. Apply a drop of blue thread locker on critical fasteners if recommended.

5. Reconnecting O2 Sensors and Heat Shields

Reinstall O2 sensors into their bungs, using anti-seize on the threads. Tighten to 22–25 ft-lb. Route the sensor wires carefully away from hot surfaces and secure them with zip ties. If the original heat shields fit over the new downpipes, reinstall them — they help protect the engine bay from heat. Some aftermarket downpipes make heat shield reinstallation difficult; in that case, consider aftermarket turbo blankets or heat wrap.

6. Lowering the Vehicle and Initial Inspection

Once everything is bolted up and all tools are removed from under the car, carefully lower the vehicle. Start the engine and allow it to idle. Inspect all connections for exhaust leaks by listening for hissing sounds or feeling for escaping air with your hand (be careful of heat). A soapy water spray can help identify tiny leaks. If you detect a leak, shut off the engine, let it cool, and retorque the offending bolt. Repeat until no leaks are present.

Post-Installation Considerations

ECU Tuning

After installing GTM downpipes — especially catless ones — the engine will run lean without a proper tune. A custom tune using Cobb Accessport or ECUTek is highly recommended to optimize air-fuel ratios, ignition timing, and to disable any emissions-related fault codes. Tuning also allows you to fully capitalize on the increased flow and power potential. Visit GTM's official product page for tuning recommendations and compatible software.

Test Drive and Monitoring

Take the car for a short test drive under varying conditions — light throttle, full throttle, and deceleration. Listen for any abnormal noises like rattling (contact with subframe or chassis) or persistent leaks. Monitor boost levels and exhaust gas temperatures if you have gauges. After the drive, let the car cool and recheck all fasteners — they may have settled with heat cycling. Retorque if necessary.

Break-In Period

Like any precision component, new downpipes benefit from a brief break-in period. Avoid sustained full-throttle runs for the first 100 miles. This allows the gaskets to seat properly and the metal to stabilize through heat cycles. After break-in, re-torque the downpipe bolts one final time.

Conclusion

Installing GTM GT-R downpipes is a rewarding upgrade that instantly enhances the driving character of your Nissan GT-R. By following this detailed guide, you can perform the installation with confidence, knowing you have the necessary tools, safety precautions, and procedures. Always work methodically, double-check your work, and consult a professional if you encounter stubborn bolts or ambiguous steps. For further assistance, GT-R forums like GTRLife provide a wealth of community knowledge and troubleshooting advice. Enjoy the new sound, responsiveness, and power that proper aftermarket downpipes deliver.