Guide: RB25 Swap Wiring

[judasentinel]

BULL S H I T!! Youre right. They are the same........you can use the CAS interchangeably between RB20 and RB25/

R34 had the black CAS (Hitachi), which is different from what R33 and R32 use.

[spank110]

Just a heads up, we just did the swap using an Automatic 4WD rb25 with an rb20 harness and ecu with nistune.

Because of the pickup location, We just used the awd aluminum oil pan and removed the axels and diff. Then cut the housings off and ground it smooth so just the casting for the oil pan remained.

Because it came from an automatic, before you can install the pilot bushing you need to remove the collar in the crank.

Also, haven't heard this mention anywhere else, maybe its because of the AWD or AUTO, but neways to use the RB20 TPS we had to build a hybrid throttle body of the two. The rb20 TPS mechanical input is a round shaft with a flat side. The rb25 throttle body's mechanical input uses a round shaft with a pin through it.

---To do this we used the rb25 throttle body housing, disassembled it and tapped out the shaft, replaced it with the rb20 shaft (center it). The rb20det shaft uses a thicker throttle plate but is also 65mm so it needs to be swapped over also.There is a metal sleeve that sits under the springs on the rb20 throttle body. Swap this over, then use the rest of the components of the rb25 throttle springs/ linkage the same way they came off. Install the rb20et TPS and its good to go.

One more thing, the crank pulley on our engines' power steering track was a for a 3 groove belt an the power steering pulley from our rb20 was for a 4 grove belt, so if you run into this just swap the crank pulley from the rb20 on.

[Mitchguy]

i recently did the swap, used the rb20 wiring harness and rb20 ecu and my car was running fairly rich.. what should i do about this

AEM air to fuel gauge?

[love_boost]

unless i read wrong i think you need the rb25 ecu or your rb20 ecu tuned?


what would happen if i bought a conversion harness for the rb25? could i just rip my olf harness out and in with the rb25 one and it would be fine?

[APL]

Get your rb20 rom chip tuned, nistune, an rb25 ecu(wiring) or yeah some other engine management.

[judasentinel]

to mitchguy:

You need to find a way to cut back on your fuel delivery. When you use an RB20 ECU to run an RB25, it is like running an RB20 with 370cc injectors. Since the RB20 ECU runs on the 270cc injector level, it does not know the injectors are of a larger size. Plus, even when the O2 sensor tells it is running rich, it only does so until the engine reaches 30 degrees Celsius, after which O2 sensor feedback system is disabled.

The best thing to do is get Nistune or a chip (Stinky tune is a great chip - Braden Huffman aka skylinegtr20 is selling it, I think) and if you cannot do that, then get an SAFC II (not neo, as I dont like that there is only ONE map setting in it, compared to two different settings on the SAFC II). I am not the one for any kind of a piggyback system.

Using the RB25 ECU with the RB20 harness or the RB25 harness will not work properly. If you want to run this ECU, you have to get a custom harness made out of the Rb20 and Rb25 harnesses.

Rb20 ECU to me is the best choice, with Nistune installed on it.

[bignate]

Resurrecting this because I found its not quite as simple as the original post suggests. In addition to rewiring the injectors you also need to rewire the ignitor as the RB20 harness has a 6 pin plug and the rb25 ignitor uses a 7 pin. Ideally you need both harnesses.

[APL]

You just use the full rb20 harness w/ rb20 ignitor and you need the rb25 injector plugs w/ the injectors, then switch injector wires #4 and #6 at the ecu. This is all the wiring that is needed, you dont need both full harnesses.

[bignate]

You just use the full rb20 harness w/ rb20 ignitor and you need the rb25 injector plugs w/ the injectors, then switch injector wires #4 and #6 at the ecu. This is all the wiring that is needed, you dont need both full harnesses.

I didnt have a rb20 ignitor, so I woulda been SOL.

[BrianV8]

Why is it you have to swap injector wires 4 and 6? Are the firing orders of the motor not the same? And you used the rb20 ecu correct?

[APL]

The pins on the ecu are switched. The firing order idthe same though.

[BrianV8]

since the cylinders fire at the same time how would it matter what way they go? Just trying to make sence of how swapping them would effect anything.

[APL]

since the cylinders fire at the same time how would it matter what way they go? Just trying to make sence of how swapping them would effect anything.

??
The cylinders dont fire at the same time. They all fire at different times..

[BrianV8]

ohh i read the firing orders were the same , that makes sence then lol

[bignate]

LOL I think you guys are misunderstanding eachother. It sounded like BrianV8 was saying the cylinders all fire the same time, as in cyl 1-6 fire at the same time, but I think he meant both engines have the same firing order. It is simply a matter of the ecu pinout having injector #4 and #6 switched, no idea why.