Recommendations on engine swap for 525i

[Emmick68]

I have a 525i with a run down auto tranny, engine has 200k+ miles on it and leaks oil like crazy. Either way i will be getting a replacement for both or have them rebuilt. However, I was wondering if you guys have any recommendations and experience throwing a different motor and trans in there instead of the stock one without rigging up new mounts and all that jazz?

[zubbie]

The only reasonably simple upgrade is an S52. All other option require a lot of work and money. (Not that finding a good used s52 is easy).

if your engine still had good compression numbers why not just re-gasket it to fix the leaks. Find a 5 speed trans and save yourself some coin.

or drop in another M50. May be easier and cheaper in the long run

[5mall5nail5]

So many options. You can find an S52 crank, pistons, rods, and such and build an S52 or similar. You can grab M52 crank, rods, and pistons and hone the block and build a 2.8L. Etc. The only odd ball is that the M50TU uses 140mm rods - the rest of the M5x/S5x use 135mm rods.

[nonturbodan]

The six cylinder and V8 use the same front subframe. M60B40's are cheap. You could dunk that in with a 530i 5 speed and have a good old time for not much money.

[5mall5nail5]

Subframe is the same but body brackets and brake system are not. He'd have to convert to a front mount booster, etc. Not worth it.

[PetesHelga]

the most cost effective upgrade would be to buy a better car

[5mall5nail5]

the most cost effective upgrade would be to buy a better car

Yes/no.

[E38740iMD]

Yes/no.

[bebout]

I swapped in a low mileage M52. Pretty simple swap and you can find them fairly cheap.

[BleedsBlue]

I'm local to you, OP, and know first hand of a couple solid S52s for sale. That's certainly what I would do, though John also has a good idea--these M50-based motors are largely like Legos in terms of different rotating assemblies, camshafts, etc, all being interchangeable with mild work during a rebuild.

FWIW regarding the B40 argument; a local S52 and 5 speed-swapped touring was no match for a local (read: in my garage) B40 auto touring, both with quicker diffs. May be anecdotal but as discussed in a recent thread, stock for stock the B40 is much stronger.