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E34 525 M20 to M50 swap

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E34 525 M20 to M50 swap

Postby KowKow » Sun, 19 Mar 2006 14:57:30 UTC

Hello all,

I've recently bought a 1990 E34 525 with an M20 engine and would like to replace the motor with an M50 version, would this be a more or less straight swap?

To summarise....

a)Would I have to replace the whole loom & ecu, or just replace the chip
b)Are the engine mounts the same?
c)Are the gearboxes the same incl. prop?
d)Is the exhaust manifold the same?
e)or, should I just forget the swap and chip the M20 to get it closer to M50 bhp?

I realise the best thing would be just to buy a more recent E34, but the bodywork and condition of the car is really good so that really wouldn't be an option.

Just to mention that I have trawled the posts already and haven't really come up with the answers - in case you thought this was a lazy post!!

Thanks in advance.

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Postby KowKow » Sat, 25 Mar 2006 11:48:23 UTC


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Postby Guest » Sat, 25 Mar 2006 12:21:11 UTC

you would need the engine loom, the ecu and all associated parts.

Postby machinehead525 » Sat, 25 Mar 2006 14:35:25 UTC

m50 has 6 coils, not a distributor, so complete engine loom and ecu change for sure. prob airflow meter too to go with the ECU. With the info feed back to dash display this may cause additional complications too.

to be honest I'm no expert but thats just a couple of thoughts :) best of luck!
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Postby Guest » Sat, 25 Mar 2006 18:23:13 UTC

the m50 deffo has a maf whereas the m20 has an air flow meter so yes, all this would need swapping.

Postby 525sport » Sun, 26 Mar 2006 00:14:12 UTC

There are so many subtle differences, would it not be considerably easier to repalce the original M20 engine with another M20 engine?

I have run an M20 engined 525i and a M50 engined 525i (with vanos) for a few years, nothing mechanical is directly interchangeable!

There are TWO versions of electrics for the M50 engine... DME 3.1 for 1991-92 and DME 3.3.1 for 1993-1995. Your M20 is DME 1.3. so you would need the loom, ECU's etc.

The M50 gearbox is different to the M20, and there are also TWO versions of that Your early 'box is a Getrag 260/5 which is an overdrive 5th gear. The later 'boxes are direct 5th with a direct top gear, so you would need to change the differential too...

Plus of course the later ECU will be expecting signals from lambda sensors, and they are located in the catalyst, so you would need a complete exhaust system change as the M20 does not have the catalyst exhaust system either...

I'm not saying it can't be done, but I can see it being a massive undertaking, probably a lot more work than you would be expecting form the outset.

I've run the M20 engine for a long time (4 years, 80,000 miles) and it is easy to work on, if you are having fuel injection problems rather than it needing a mechanical overhaul, PM me as I've diagnosed / mended mine on several occasions.

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Postby KowKow » Sun, 26 Mar 2006 21:59:27 UTC

Thanks very much for the replies. The differences between the M20 and M50 really make it an impractical swap just for a couple of extra horses and a little more engine refinement.

Mmmm, 130k miles+fast road chip=possible M20 demise.....

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