I was called by a local today i had met awhile back when i got some parts of a beat s12 (stripped drift bitch) that he bought to take the det out and put it in his Datsun Roadster. He didnt get and ECU with his motor so he was looking around online and wanted to know what all the numbers ment and which ecu would be the best.. I didnt know what to tell him so i have spent the night searching and figured i would try collect the info i found on many different forums to make thing quick and easy for the curious people like myself.
Cant wait to see that motor in this little car, Its already in and hooked up he just needs to do wiring (He estimated 2 days) and get an ECU. This is not his car but close

Back to important matters hahaha
Car Motor Trans Placement?? ECU CodesRS13 180SX CA18DET AT FR 23710-36F15 MEC-D017. 27C128 27C128
RS13 180SX CA18DET MT FR 23710-36F05 MEC-D016. 27C128 27C128
S13 180SX SR20DET MT SR 23710-50F05 K170SDM3. 27C256 M6M7256
S13 CA18DE AT FR 23710-35F11 MEC-D014. 27C128 27C128
S13 CA18DE MT FR 23710-35F00 MEC-D001. 27C128 27C128
S13 CA18DET AT FR 23710-36F11 MEC-D015. 27C128 27C128
S13 CA18DET MT FR 23710-36F00 MEC-D003. 27C128 27C128
S13 SR20DE AT FR 23710-52F10 K078PDA7. 27C256 M5M7256
S13 SR20DE MT FR 23710-52F00 K078PDM7. 27C256 M5M7256
S13 SR20DET AT FR 23710-50F10 K078ODA8. 27C256 M5M7256
S13 SR20DET MT FR 23710-50F00 K078ODM8. 27C256 M5M7256
S13 in general refers to the '88-'94 chassis, This includes the coupe and the fastback. k = super hicas, r = hatchback, P = SR20
'88-'90 S13 Silvia CA18DET
'90-'91 RS13 180SX CA18DET (R for fastback)
'91-'93 PS13 Silvia SR20DET (P for SR)
'91-'98 RPS13 180SX SR20DET
'91-'93 KPS13 Silvia (K for Super Hicas)
'91-'93 KRPS13 180SX
'89-'90 HS13 240SX KA24E (H for KA24E)
'89-'90 RHS13 240SX FB
'91-'94 MS13 240SX (chassis code for convertibles)
'91-'93 RMS13 240SX FB(M for KA24DE)
'91-'93 KRMS13 240SX FB w/ Super Hicas
'91-'93 KMS13 240SX w/ Super Hicas (Canadian market only).
'94-'98 S14 Silvia SR20DET
'94-'98 CS14 Silvia w/ Super Hicas
'95-'98 S14 240SX KA24DE (no specific S14 code for KA24DE)
Maybe i will add more info, Separate it and put it in the right sections after... For now this will due enough to make me do it eventually
Sources:
http://www.trinituner.com/v3/forums/viewtopic.php?f=21&t=314502http://www.silviawa.com/forums/index.php?showtopic=6319