Engine Swap ????

[1990e30coupe]

Ok, To start- I own an 1990 e34 with an m20b25 it just rolled to 280k miles and will not run now. I pulled the head and found it has a valve issue and that the cylinder walls are scored; therefore, get a different motor. Well I happen to have a m20b25 with 59k but I don't want to waste it on an e34 so I found another car to buy, which is an 1987 325e. for a great price. Now I know there is a compression difference, but I want to swap the eta motor into the 525i and put the m20b25 out of an 89 325i into the 87 e30. I know everything swaps I have worked on them for years, which is funny because the only thing I don't know is if the brains have to be changed or will an "I" brain run a "eta" motor and visa versa? Never ran into this being an issue till know so I know there is still a ton to learn Need HELP trying to buy car tomorrow!
Common sense say if the compression is different fuel ratio will be different, but for all I know I could just do the engine swap and not have to mess with anything else.
Also if I just unplug the motronic system and plug it into the other car will that work or can I just swap motors and be done with it.
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[jlevie]

This will be a hard swap. The M20B27 engine requires a different AFM, engine harness, and DME. But the kicker is that the transmission bell housing must have two ports for the ETA timing sensors.

Having said that you could turn the M20B27 engine into a budget stroker by using the AFM, head, intake, throttle body, injectors, FPR, CPS, engine harness, and DME from an M20B25.