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Engine Swap - Rb25det Into R32


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Hey everyone,

I currently have a '89 R32 with RB20DET 5 speed.

Im looking to swap it for an RB25DET, and im wondering ecatly what i need to do/change/have in the way of parts to do it.

Im being told alot of different things by different people, so someone who knows or has done it before can possibly help.

I have a power FC in my car now, but i realsie ill have to swap it for an RB25DET one, which is easy. Appart from changing the computer, can i just put in the RB25 loom and plug it straight into the RB25 power FC?

Does anything els ein the car have to be changed? as in wiring?

Im planning to use the RB20 gearbox and my clutch for now, and possibly just strengthen the gearbox if i can? rather than go to the trouble of putting in the RB25 one and having to change all the wirng that im told of?

Any help would be appreciated.

Btw, i have searched the forums but didnt find alot

Thanks...

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If you are using the 20 box then the hardest part is the wiring. It isn't a plug in swap. Best get the wiring diagrams, a multimeter and start tracing the 20 and 25 looms. The mechanical part of the conversion is as per the write up in the above link.

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BHDave, weren't you talking ECU box, not gearbox? Because the RB20 manual gearboxes don't have any electrics (except usual reverse light stuff), unlike the autos.

As for the gearbox, I kept the RB20 box, it's easily handling 180 Awkw.

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lol.

sorry, for everyone i confused there i will elaborate.

The conversion is much simpler from a mechanical point of view if you keep the rb20 gearbox as you use the rb20 engine mounts with the rb20 gearbox and mounts so it all lines up.

If you want to swap in the rb25 gearbox you will need to modify the tailshaft and gearbox mount so it adds to the complexity of the swap. You also have to mess around with the speedo drive.

No matter the gearbox used you will need to carry out some modifying of the engine loom. You can do it a couple of ways, either modifying the rb20 engine loom by changing a few plugs on the engine side and adding/swapping a few pins at the ecu so you can plug in the rb25 ecu or my prefered way which is use an rb25 engine loom and modify it to plug into the rb20 body loom (2 under dash plugs and the main power feed near the airbox in earlier model gtst's, 4 under dash in later ones plus adding a dropping resisor for the fuel pump and wiring in a water temp sensor for the climate control).

Which ever way you do it, keep the rb20 section of loom that runs to the gearbox, alternator and oil pressure sender.

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I have undertaken the same conversion as BHDave and modified the RB25 loom to make it a 'plug'n'play' loom (ie graft the RB20 body loom plugs into the RB25 loom). In my opinion this is the neatest approach as you can utilise the VCT and boost solenoid which only the RB25 ECU will control.

I concur with BHDave's comments re the RB25 gearbox issues and furthermore can add that a new speedo drive will be required and the speedo cable shortened in order to finish the job neatly.

I made a custom mount for the RB25 gearbox - refer member gallery. You should consider what power you wish to ultimately achieve with the motor before forking out good money on an RB25 gearbox if the RB20 box will suffice.

If you would like some assistance modifying the looms or would prefer someone else to do it, I would be happy to help. I have just finished a loom for another member who is currently putting an RB25DET in his RB20DE Cefiro.

Hope this helps.

Cheers

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Thanks for all the replies guys,

My main convern is that the RB20 box will break easily. I have already broken one, i think due to the button clutch i have, and i now only hvae like 175rwkw. Im thinking its all the drifting.

Anyway, if i was to go down the road of an RB 25 gear box, i would have to get a new tailshaft, or modify the one i have?

What sort of money am i looking at to get an RB25 box?

Im pretty much looking to get a workshop to do most of the work.

Thanks

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I have undertaken the same conversion as BHDave and modified the RB25 loom to make it a 'plug'n'play' loom (ie graft the RB20 body loom plugs into the RB25 loom). In my opinion this is the neatest approach as you can utilise the VCT and boost solenoid which only the RB25 ECU will control.

I concur with BHDave's comments re the RB25 gearbox issues and furthermore can add that a new speedo drive will be required and the speedo cable shortened in order to finish the job neatly.

I made a custom mount for the RB25 gearbox - refer member gallery. You should consider what power you wish to ultimately achieve with the motor before forking out good money on an RB25 gearbox if the RB20 box will suffice.

If you would like some assistance modifying the looms or would prefer someone else to do it, I would be happy to help. I have just finished a loom for another member who is currently putting an RB25DET in his RB20DE Cefiro.

Hope this helps.

Cheers

Dude... if only you lived in melbourene!

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You can modify your existing tailshaft.

A specialist like hardy spicer (they're in sydney unfortunately) can do the work for you. Best to speak to someone before hand to find out the measurements they require so it can be done once the engine has been dropped into the car (so you can measure) but while you are still finishing everything else (so it doesn't hold up the process).

They will have a new spline section and yoke and uv joints in stock to make it all work.

I've seen 25 boxes go for anywhere between 1000 and 1500 from importers. My 20 box is still alive with 238rwkw so i don't see a swap as really necessary myself.

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  • 2 years later...

I just got my RB25DET (series 2) and I was hoping you could help me with some questions.

My Skyline is non turbo so it will be a big step with the RB25.

Now then, my first question is about the gearbox mounts, I hear they aren't the same and I will also have problems with the speedo meter. What do you know about this? Can I use the Xmember of the R33 ??

The second is about the harness, everyone that has ever swapped an engine told me that the harness is the most difficult part of the swap. Do you have the diagram of the R32 and the R33 (still can't find it for the R32) and some pointers on how this is done??

Hope to get a reply from you soon

Carlos Rudolph

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