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Guide: RB25 Swap Wiring

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  • Guide: RB25 Swap Wiring

    Well, there seems to be a certain amount of confusing regarding wiring when doing the RB20 -> RB25 swap.

    I read quite a few conflicting things in my search for accurate information, and at the end of the day i just looked over the wiring diagrams, and plugs on the harness, and used little bits of information i read.

    So with that, i'm going to post everything you need to do (which is really not much at all). swapping from rb20 to 25 is about the easiest wiring swap you could possibly do. This makes swapping a SR20 into a 240sx look like rocket science.

    Details on the particular swap we did:

    RB20 GTS4 AWD -> RB25 RWD.

    The car's getting re-swapped for a rebuilt rb25 with modifications to the block to fit the awd system, or a rebuilt rb26. in the near future.

    Anyway... onto topic here:

    Wiring the car, using the RB20 harness, as its 100x easier, and has no downsides.

    You will need:

    -Complete RB20 harness including injector sub harness
    -RB25 injector sub harness.
    - (optional) a plug that will fit onto the VVT solenoid, and some wire.

    1) Take the injector sub harness off the RB25. This is the one with the plugs for the sidefeed injectors.

    2) Cut all the plugs off, leaving enough wire to solder them onto the rb20 harness.

    3) cut off all the top feed plugs on the RB20 harness. 3 are on the sub harness, and 3 are on the main harness.

    4) Solder the sidefeed injector plugs onto the RB20 harness and sub harness.

    5) You must swap the wires for injectors 4 & 6. Doing this at the ECU is the easiest Just cut pin 112 & 114 and cross them and resolder.

    If you have an afermarket ecu (such as in the case of this install), and you can configure your outputs, you can do this in software. In our case we used an AEM EMS... its nice because it supports the RB20, 25, and 26 with one unit.

    6) If you want your VVT to work, you must get a hold of the right connector for the VVT solenoid. If you have an rb25 harness, thats easy just take it from there, if not take a trip up to the wreakers and snag one off some random nissan that will work.

    Then just solder 2 wires to it, plug it into the solenoid, and wire it up into the ecu. We didnt hook it up, so i'm not sure on the exact wiring. I do know pin 113 is a trigger for the VVT. It would be easy to figure out with a wiring schematic. If you need help with this, post a schematic that includes the VVT solenoid on it, and i'll tell you how to wire it.

    7) Your done. Make sure you use an RB25 ecu or calibration.


    If anyone has any other questions regarding this swap let me know, while its still fresh in my mind

  • #2
    Does it matter if I use a series I or series II ECU for the RB25?? also do you know what i should do if i have an Auto engine but using a 5MT??
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    • #3
      Originally posted by C-unit View Post
      Does it matter if I use a series I or series II ECU for the RB25?? also do you know what i should do if i have an Auto engine but using a 5MT??
      Usually auto ECU will work with MT. MT ecu will not work with auto ecu. Other than that you'll need a MT flywheel and clutch. You'll also need to put in the MT pilot bushing.

      Sorry i am not 100% on the differences between the series 1 and series 2.

      The aem ems that we were working with was capable of running any rb25 up to 1998. From this, i assume if its past 1998 (this would be the neo?) it requires a different ecu, but other then that it wouldn't matter. I am assuming this, i don't actually know for sure, as the a/m ecu is definitely much more flexible in what it can run.

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      • #4
        stickied?!


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        • #5
          Sticky this fantastic post
          91 GTST Type M

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          • #6
            yo u can also use the rb20 ecu seeing as how its easier to chip tune .
            and run the vvt off a switch.. like a rpm switch and have it work when u hit a certain rpm .
            i have a top feed setup for my injectors also so i just used the exact same wire harness .
            Its Crack
            91 R32 GTS-TM ---RIP------
            93 R33 GTS-25t ---SOLD----
            93 R32 GTR ---FOR SALE----

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            • #7
              good post!! Im glad some one finally put this up
              Im still building my 25 but this will come in handy in a month or so

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              • #8
                rb25 gts-4. 2.0 to 2.5

                What block modifications did you have to do to make the Atessa 4WD work. I currently have a 1991 GTS4 with no compression in one cylinder and no more than 125 psi in any of the others and wanted to swap in the RB25. Did you use an engine from an R33gts-t? Or a Stagea that originally has 4WD. I heard this swap was a knightmare for wiring and an axle mod was also needed. Thanx.

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                • #9
                  Originally posted by SASEC View Post
                  What block modifications did you have to do to make the Atessa 4WD work. I currently have a 1991 GTS4 with no compression in one cylinder and no more than 125 psi in any of the others and wanted to swap in the RB25. Did you use an engine from an R33gts-t? Or a Stagea that originally has 4WD. I heard this swap was a knightmare for wiring and an axle mod was also needed. Thanx.
                  The easiest swap for you would be to pick up a R33 GTS-4 Engine ( RB25DE ) and then build it so it can handle boost. The only turbo RB25 4WD engine is from the stagea as you stated, pain in the ass wiring.

                  But then you might as well drop a RB26 into it.
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                  • #10
                    Originally posted by SASEC View Post
                    What block modifications did you have to do to make the Atessa 4WD work. I currently have a 1991 GTS4 with no compression in one cylinder and no more than 125 psi in any of the others and wanted to swap in the RB25. Did you use an engine from an R33gts-t? Or a Stagea that originally has 4WD. I heard this swap was a knightmare for wiring and an axle mod was also needed. Thanx.
                    To be completely honest with you, you're going to save money going with an RB26, and get better results.

                    A decent RB26 can be had for under $2500 and it will drop right in with your tranny. Harness should require minimal modification.

                    RB25 you have to fill the existing holes along the sides, and on one side you need to fabricate a block extension that fits the coutures of the block and is capable of sealing oil. From a machining standpoint it would take a day for someone competent to do it (but i'm talking a full day, like 8hours or possibly more). After all this you need to mark, drill and tap holes for the studs and bolts of the AWD pan.

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                    • #11
                      Thanks for the tips. That should help me get started.

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                      • #12
                        Hey, I also re-checked the ECU pin outs .....I wondered why the injector wires had to be crossed

                        R32 inj pin

                        INJ 1 = pin 101
                        INJ 2 = pin 105
                        INJ 3 = pin 103
                        INJ 4 = pin 112
                        INJ 5 = pin 110
                        INJ 6 = pin 114

                        R33 inj pin

                        INJ 1 = pin 101
                        INJ 2 = pin 105
                        INJ 3 = pin 103
                        INJ 4 = pin 114
                        INJ 5 = pin 110
                        INJ 6 = pin 112

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                        • #13
                          The aac valve on the rb25 has 2 plugs, where as the rb20 has 1. Im guessing the second plug doesn't matter?

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                          • #14
                            No, the second plug doesn't matter at all. If you're using the RB20 harness, you can leave it as is.

                            I think the most critical issue with this swap is the ECU that you will be using. If you use RB25 ECU, there is a bit of wiring that needs to be done, especially if you are using the RB20 harness. But if you use the RB20 ECU, there is NO NEED to swap out anything except the injector plugs. Everything else is a straight plug and play.

                            Do not be fooled by anyone who says that there is something else that needs to be done if you use the RB20 ECU. There isn't.
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                            • #15
                              Ive also heard some **** that the r32 cas will not work on an rb25. Someone want to clear this up? Im almost positive they are the exact same cas, the r34's used a cas from a different manufacturer.

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