Finally found it 36 pages into the RB30 thread lol
from sk...
Hi guys, whilst GTR- Ben is almost right, it is actually the sensors you use on the engine that determine which ECU and loom you use. As an example we have an RB31DET (RB30 at 3.1 litres with an RB26DETT head) that uses an RB20DET Power FC and the original R32 GST loom . What I have done is use all of the sensors off the old RB20DET on the RB31DET. I swapped over the water temp sensors, knock sensors, throttle position sensor, CAS, boost sensor, oil pressure sensor, AFM (we used a Q45 AFM) etc. Plus I used the 565 cc injectors that were in the RB20DET, which were top feed and high impedance to match the Power FC.
I did it this way, rather than use an RB26DETT ECU and loom, because I already had an RB20DET loom and Power FC in the car. So it seemed simpler to swap the sensors and injectors over while both engines were out of the car. Plus I am not very good with looms, I never seem to be able to get them to fit back in the way they should.
If I had an R33GTST I would have done what GTR-BEN suggested and used all the original stuff with the RB30 bottom end.
Hope all that makes sense.