Nissan GT-R Fuel Injector Installation

Stock Injector Removal

With your car parked in a flat, level area go ahead and remove the fuel cap. This process should release most of the pressure built up into the fuel system.
Popping open the battery cover, Using a 10mm wrench, unhook the negative terminal of the battery.
With a 5mm Allen wrench or socket, remove the engine cover. Make sure not to lose the metal spacers out of the bottom as digging things out of the engine bay can be a huge pain!
Using pliers to loosen the hose clamps, remove all of the vacuum lines on the intake manifold, there should be 3 on the driver's side (USDM) and one on the passenger's side along with one in the back.
Using a Philips screwdriver (or a 7mm / 8mm socket depending on the clamp) loosen the throttle body coupler
Note: On 2008-09 MY vehicles there will be a coolant line attached to each throttle body, for this reason in many instances it's easier to unbolt the throttle body from the manifold itself, in which case you can simply skip step 5 and 6
Using a small pick or your fingers, unhook the wiring for the throttle body by depressing the connection and carefully pulling out on the connector.
Using pliers squeeze the clamp together for the recirculation pipe, and pull the tube off of the bypass-valve, once done you can wiggle the whole tube free and roll it to the side and out of the way.
With the charge pipes out of the way unhook the MAP sensor on the passenger's side of the manifold.
Using a trim pry tool, carefully pop the wire ties out of their mounts on the back of the manifold.
Depressing the clip in the center of the hole, pull up on the harness so that it is no longer attached to the mount.
Moving over to the front of the intake manifold, unbolt the two 10mm bolts holding the cross-over pipe in place and gently pull it out of the way. Pulling the check valve out of one end of the line can make it easier to get fully out of the way.
Using a 10mm socket, remove the 8 bolts holding the upper half of the intake manifold on. Once done, carefully remove making sure not to pull on any harnesses or lines.
Pressing on the clips release tab, remove the clips off of each injector.
Remove the two bolts on the passenger side and the three bolts on the driver's side from the fuel rail using a 12mm socket. (picture is for reference, removal of the fuel rail from the car is not necessary)
Pull up on the fuel rail to release the injectors from the intake manifold, now is a good time to put a rag underneath the injectors to keep any fuel from flooding into the cylinders since there will likely still be some remnants in the lines.
The injector clips are U shaped, so you can simply pull them away from the injector body using some needle nose pliers in order to release the injector.
Double check both ends of the injector to make sure all of the o-rings came out. Sometimes on older cars they can come apart and stay in place, and you don't want them to end up in the cylinders or going through your turbo.

Injector Installation

Go ahead and lubricate the injector o-ring using either some super-lube or petroleum to ensure a good injector sale, and to make sure the o-ring doesn't fold or crimp during the install.
Once lubricated install the new injector in place.
After swapping in all the injectors, carefully push down on the fuel rail and make sure the injectors are all seated properly.
Install the adapter harnesses, you may need to re-clock the injectors slightly for everything to fit in place without hitting the manifold or fuel rail.
After that you can carefully tighten the fuel rails back down to 7 ft/lbs (10Nm) and then 16 ft/lbs (22Nm)
You can now reinstall the rest of the items in the reverse order of removal, tightening the intake manifold to 9.5 ft/lbs (13Nm) from the middle of the manifold outward alternating sides to make sure the gasket tightens evenly.
You're all done! Flash the appropriate tune on the car for your injectors and then enjoy!

Calibration

Change the injector scaling

After the physical installation of the new fuel injectors has been achieved, you will need to modify three settings in the injector maps of the ROM file:

Maps by Function ⟶ Fuelling ⟶ Injectors ⟶ Injector Flow Scaling (RaceROM)
Original value: 570
New value: 975
Maps by Function ⟶ Fuelling ⟶ Injectors ⟶ Injector Lag Time Offset
Original value: 0.890
New value: 1.0
Maps by Function ⟶ Fuelling ⟶ Injector Minimum Open Time
Original value: 1.83
New value: 1.0

First check the box next to the setting, then on the pop-up window click Edit -> Fill Selection with Value, enter the new value and click OK to proceed. Repeat the procedure for the each of the settings above.

The following screenshot shows the maps after all changes have been made.