5C1201 - COBB Nissan GT-R Cast Bellmouth Downpipes

5C1201 – Nissan GT-R Catted Cast Bellmouth Downpipes

Nissan GT-R 2008-2018

Nissan GT-R Catted Cast Bellmouth Downpipes

Congratulations on your purchase of the COBB Tuning GT-R Downpipes! The following instructions will assist you through the installation process. Please read them BEFORE beginning the install to familiarize yourself with the steps and tools needed. If you feel you cannot properly perform this installation, we HIGHLY recommend you take the vehicle to a qualified and experienced automotive technician.

IMPORTANT! Installing this kit will require custom tuning or utilizing an appropriate Stage Power Package map if you have a matching mechanical configuration. Please consult with COBB or an authorized ProTuner in your area if you have any questions!

Table of Contents

Parts List

  • Passenger Side downpipe
  • Driver Side downpipe
  • (2) 3" exhaust gaskets
  • (4) m10 x 35mm flanged bolts
  • (2) m10 x 20mm flanged bolts
  • (6) m10 flanged nuts

Tools Needed

  • 3/8" ratchet

  • 3/8" 10mm socket

  • 3/8" 12mm socket 

  • 3/8" 14mm socket
  • 3/8" 2" extension
  • 3/8" 14mm swivel socket
  • 3/8" 8mm socket 

  • 3/8" 12" extension

  • 3/8" 6" extension

  • 3/8" universal swivel
  • 1/2" breaker bar*
  • 1/2" 16" extension*
  • 1/2" 14mm socket*
  • 14mm offset wrench
  • Oxygen Sensor Wrench
  • Trim tool
  • Anti-Seize
  • Penetrating Oil


  1. Lift up the battery cover and using a 10mm wrench disconnect the battery

  2. While the vehicle is on the ground, unplug the oxygen sensors from the engine bay and make sure the wire is detached from any wire clips as you will be pulling the downpipe out with the oxygen sensors in them.

  3. Jack up the car, pay careful attention to jacking points on the car to prevent damage to the carbon fiber undertray.  Make sure the vehicle is in neutral in order to more easily remove the front propeller shaft later.

Undertray Removal

  1. Using a 12mm socket and an extension remove the 4 bolts from each side (2012+, 2008-2011 vehicles will have 3 on each side) of the cross brace and the one 10mm bolt in the center holding it to the undertray.

    NOTE: During the install you'll have multiple sizes of 10mm bolts so make sure to keep them sorted to make sure they go back in the same spots.

  2. Remove the 5 plastic clips from each side holding the inner fender lining to the undertray.  Using a trim tool pull up on the center part of the plastic clip to relieve pressure, then place the tool underneath the base and gently pry upward to pop the clip out.

  3. Remove the 10 bolts from the undertray using a 10mm socket.

  4. Set the Undertray in a safe place to avoid tripping over it or breaking it.

  5. This is a good time to add penetrating oil to the bolts for the 7-pipe and where the downpipe meets the turbo.  Since the exhaust components hit pretty high temperatures it is pretty common for bolts to be seized so spraying them down with something and taking a lunch break or even waiting overnight can help things run a lot more smoothly.

Y-pipe Removal

  1. Support the y-pipe using a jack.

  2. Using a 14mm socket undo the 2-bolts where they meet the cat-back portion of the exhaust, and the 4 nuts where the y-pipe meets the downpipes.  

  3. With it still supported, wiggle the Y-pipe to pull it free from one end (the cat-back portion is typically the easier end) and take the entire unit out of the car.

Downpipe Removal

This part can get frustrating very quickly.  Make sure to take your time and when in doubt, add more penetrating oil or get skilled help.  These bolts can easily become stripped which will require pulling the entire engine to fix, so patience is key!

  1. Reach over the driveshaft and disconnect both rear oxygen sensors.

  2. Remove the bottom bracket supporting the downpipes to the bellhousing using a 14mm socket.

  3. Disconnect the front propeller shaft that goes to the passenger side (USDM).  Make sure to make an alignment mark on both sides to ensure it is lined up in the same orientation when you reinstall.  This will require the removal of 4 12mm nuts.Complete removal is not necessarily, you can just unbolt it where it meets the front of the car and move it to the side.

  4. Using the 14mm offset wrench remove the lower nuts from the downpipe where they are covered by the catalytic converter.

  5. Employ your 14mm socket and the 3/8" ratchet to take off the remaining easy to get to bolts

  6. Now for the fun part!  Getting to the bolts you can't see is going to be a test in patience.  Using the 3/8" ratched with the 16" extension and 14mm swivel socket  (or socket and joint) work on the inner bolts.  Going from the top parallel to the main driveshaft works well, however other approaches may be more successful for you.  For the bolts that are really on there, you may need to utilize the 1/2" breaker bar, extension, and socket to get the bolts loose.  Do your best to not go too crazy, as damaging the bolts or studs can be expensive and incredibly difficult to fix.

  7. Once unbolted wiggle the downpipes out through the space that you have.

  8. Let out a deep sigh of relief that you're finished with this monstrous task and that the cats are smaller on the new downpipes so you can more easily get to everything.


  1. Once free from the engine bay, use the oxygen sensor wrench to remove the oxygen sensors

  2. Unscrew the oxygen sensors from the stock downpipes

  3. Making sure to keep their positions the same, apply fresh anti-seize to the threads and swap them on to the new downpipes.  Torque to 37 ft-lb.  (This is also a good time to replace the oxygen sensors as they are otherwise going to be a pain to remove and replace in the future).

  4. In anticipation of installation, put anti-seize onto the threads of all the studs on the turbo as well as the bolts you're about to install.

  5. Loosely bolt the downpipes back on to the turbo using the new gaskets and the original studs and nuts.

  6. Torque the downpipes to the turbo in to 18 ft/lbs first then 36 ft/lbs.  Do this skipping every other bolt going around in a circle until you tighten all of them.  This helps the gaskets seat evenly.

  7. Reattach the support bracket to the downpipes using the two M10x20mm bolts and flange nuts.

  8. Reinstall the front propeller shaft and torque to 29 ft/lbs

  9. Plug-in the rear oxygen sensors and do your best to push the front oxygen sensor wires up as high as you can in the engine bay so you can reach them from the top.

  10. Using a jack (or friend) to hold the y-pipe in place, use the new gaskets and four, 35mm long bolts to attach the y-pipe to the downpipes.  This will require the 14mm socket and 3/8" ratchet. Torque the y-pipe to the downpipes to 39 ft/lbs, you'll want to torque the bolts to the catback to 26 ft/lbs

  11. Reinstall the front brace and torque to 26 ft/lbs

  12. At this point you should be okay to go ahead and put the rest of the undertray components back on, in the opposite order they were removed.

  13. Reconnect front oxygen sensors

  14. Reconnect the battery.


Calibration Map Notes for Nissan Vehicles

Helps to figure out which map you should be on given the parts installed to your car 

COBB Product Install Instructions for Nissan Vehicles

Main page for Nissan Installation Instructions

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