E30 M20B20 and M20B25 engine differences

[e30austin]

Getting ready to tear into a big project and wanted to clear some things up before hand.

I have a customer with an '87 325is that was S52 powered that I'm putting back to stock. I have an M20B25 long block (bare) and a complete '88 M20B20/5-speed out of a touring that is getting aforementioned S52. I need to know what I can and cannot use off the B20 to make the B25 a complete engine.

I know the cooling system (water pump, radiator and the three hoses on the front of the engine) is different, as well as the intake manifold (smaller ports). I know all the accessories (starter, p/s pump, alternator, etc), valve cover, oil pan, etc are the same. I'm not sure if the wiring harness is the same - I have both '88 B20 and '88 B25 engine harnesses at my disposal, but would like to use everything off the known good, running engine.

I guess my question is: "What can I take off the B20 and install on the B25 to make it a complete engine?"

Thank you!

[packratbimmer]

Not much of anything unfortunately.

http://www.e30tech.com/forum/showthread.php?t=52085

[e30austin]

Thanks for the reply, but I'm well aware of the internal differences. I need to know what I can use as far as accessories, exhaust, wiring, etc and other bolt on external parts...

[digger]

according to realoem harness are same p/n. seem to recall should use b25 ecu as the chip is different

[e30austin]

Thanks!

[Hooffenstein HD]

Water pump and hoses should be the same unless it has one of the small non ac radiators. If that's the case, I believe the top hose is the one to use with an M42 radiator.

Or does it have an early cooling system on it with twin outlet water pump?

[jeffnhiscars]

according to realoem harness are same p/n. seem to recall should use b25 ecu as the chip is different

I would think the b20 has motronic 1.0 which means an ecu swap would require a matching harness. Of course if the 2 harnesses are truly the same this won't apply but it's something I'd check when you are dealing with swapped cars.

[e30austin]

Water pump and hoses should be the same unless it has one of the small non ac radiators. If that's the case, I believe the top hose is the one to use with an M42 radiator.

Or does it have an early cooling system on it with twin outlet water pump?

It was a small one core baby radiator. The hoses and stuff all look much different than a B25 car. I've got a late radiator I'll use, so no big issue there. It came from an '88, so it had the late water pump.

[cory58]

Radiator went bad on my 88 320i Touring w/AC. Local Bimmer shop replaced it with US-spec radiator, which was larger. They had to remove a blanking plate to fit the larger radiator, but only one hose had to be changed (upper radiator hose). Other hoses were reused.

FWIW - I can confirm that the AFM was different on my b20. Not sure what's different, but it does have a different part #.

I'm also interested in this thread, since I may decide to swap the b20 for a b25. Would be a huge plus if the wiring harness is the same.

Cory