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DIY: Top Feed Injector Conversion Under Stock Plenum with No Shaving/Mods etc.

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Original article here: http://www.trak-life...kyline-rb25det/


Just about every car enthusiast with their offensively powerful turbocharged vehicle will eventually hit a brick wall with the fuel demands by their motor. Question is, do you stop there? Certainly not! Time to get that fuel system up to scratch and invest more money into your prized depreciating asset that upsets the other half. (In our defense though your pride and joy will probably cost you less than your partner’s wardrobe and will have better resale value so you can use that excuse next time.)

As you may know, Nissan decided their humble R33 GTS-t should use side feed injectors for whatever reason and yes finding ways to upgrade to better modern better flowing injectors is a nightmare. Often people would make the choice of going high flowed side feeds (milling out the stock injector). However this has many issues which predominantly revolve around spray pattern, consistent fuel delivery and failure. All of which the Fridge unfortunately suffered from recently – hence the conversion to top feeds instead.


So chances are if you’re reading this article you’ve either maxed out your current R33 GTS-T Skyline injectors and are looking to upgrade your injectors the right way OR gone high flowed side feeds and absolutely hate it. Then again you could be an avid trak-life.com supporter and just like reading our articles.



Rest assured, this guide should give you plenty of information on how to convert your annoying side feed injectors to top feed injectors and you’re under safe hands.


Parts Required:

  • 6x Top Feed 1/2 Height 14mm Injectors
  • 6x 14mm to 11mm converters/spacers
  • 6x EV1 to JECs Connectors
  • 1x 11mm Slim RB25DET Fuel Rail & Fittings
  • 2x -6AN to 3/8” Barb 90 Degree Fittings
  • 1x 1/4npt grub
  • 2m of EFI Fuel Hose (preferably E85 compatible)
  • 4x EFI Fuel Hose Clamps
  • 1x Fuel Pressure Regulator
  • 1x Fuel Pressure Gauge
  • Some form of lubricant


  • Socket Set
  • Allen Key Set
  • Spanner Set
  • Phillips & Flat Head Screw Drivers

Duration: 3 Hours (excluding time to remove old injectors & rail)

Difficulty: Medium

Profanity Level: Medium

Prerequisite: Stock Fuel Injection system removed

So now that your engine bay is looking empty with the fuel injection system missing and your throttle body removed, it’s time to get cracking. But before anything, take a deep breath and brace yourself for a few hours of swearing. Upside, look at all that room for your top feed injectors!



Step 1:

Clean and fit the male to male fittings to the end of the rail, make sure there’s enough force to crush the crush washers if not you may be prone to having fuel leaks. At the same time, fit the grub screw to the top of the rail (if you’re not using this port as a fuel return)



Step 2:

Lubricate the injector bosses and slide the o-rings on, taking as much care as possible to avoid dust/grit between the boss & o-rings


Step 3:

Clean the plenum injector seats and carefully install the injector boss & o-ring for each cylinder on the plenum. This is best done by applying a thin layer of oil on the seats and using a cloth to gently push in the injector boss. Do not rush this, as it’s air tight it will go down very slowly.


Step 4:

Start by lubricating the top injector collars and inserting them into the rail. The use of motor oil is more than sufficient. These collars should just slide into place with not much issue once lubricated.


At the same time lubricate the injector top & bottom o-rings and test fit them. You may admire your artwork if you choose.


Step 5:

Fit all the injectors into the injector boss for each cylinder, this step might be a little tricky as there is very limited room available – however with the aid of a few beers this may reduce stress levels


Step 6:

Time to get the rail on, but before that make sure you have slipped on the correct bolts into the bottom row as it will be nearly impossible to slide the bolts on once the rail is on the plenum & injectors. Carefully lower the rail in place and start with applying light pressure on cylinder 6 and gradually working your way to the front. Once complete it should look flat and not touch anything.



Step 7:

Align all the injectors so the connectors face upwards and predominantly vertical (not essential). Wriggle the bolts out nearly all the way and slide in the shorter spacers down. Once ready bolt up from the middle up and then the outer bolts lasts using a 90 degree Allen Key (possible to use a Hex Head socket, however there is quite limited room).




Step 8:

Time to get the fuel feed sorted, attach and secure fuel hose to the fitting and attach it to the back of the rail then feed the hose back to the top of the fuel filter. Cut to length and attach.


Step 9:

Now to get the return line sorted, attach and secure fuel hose to the 90 degree barb fitting and attach it to the front of the rail. Cut the fuel hose to length then feed this hose to the Inlet Side of the fuel pressure regulator.


Step 10:

Using the convertor connectors, attached to the factory harness. Using some silicone spray will greatly help with this process.



Step 11:

Connect all the injectors back to the harness, make sure it is in the correct order or else you’ll have issues with your car running correctly. Connect the injector harness back to the main harness


Step 12:

Attach/extend vacuum hose back to fuel pressure regulator, attach the return line and mount fuel regulator in a sensible location as adjustments will be required


Step 13:

Re-attach throttle body and all required hoses/lines

Step 14:

Before starting, make sure the fuel system has been primed to remove all the air pockets. This can be done by flicking on the ignition without starting the car multiple times. You should be able to hear air pockets flow back into the fuel tank. At the same time it is wise to roughly adjust your fuel pressure to 3bar OR 43.5psi without the engine running.

Step 15:

Time to rescale the ECU to accept the new injectors, this can be easily done if you have access to your ECU’s programming interface if not time to tow your car to the tuner!


Step 16:

Start your car, it should fire up instantaneously and purr if the injector scaling is correct!


Step 17:

Time to recheck the fuel pressure once again, it should ideally show 3bar minus total vacuum at idle, i.e. 2.6 bar OR just disconnect the vacuum hose and adjust the regulator so it display 3 bar at idle.


All done! Time to enjoy your new injectors and screw in more boost (and a good tune too).

  • Upvote 1

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Solid article. Good work John!

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+1 very nice... I'll be doing a topfeed conversion on my 1jz sometime very soon... this article makes it look very easy

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