Track every stage of the engine swap — from sourcing the donor M50/M52 to first startup. Progress saves automatically.
Swapping the single-cam M43 for a twin-cam M50 or M52 is the most common E36 engine upgrade. The M43 and M50 share the same block dimensions and mounting points, which makes this a straightforward swap for a four-cylinder car. The M50B25 (170 hp) and M52B28 (193 hp) are the most popular choices — both fit without chassis modification.
The main complexity is electrical. The M50/M52 uses a Siemens DME (MS41/MS42) with a dedicated engine loom that does not share connectors with the M43 setup. You need the complete loom from the donor car, plus the matching ECU (DME) and instrument cluster for correct speedometer and rev counter calibration. The M50 also brings EWS (engine immobiliser) from 1994 onwards — the EWS module and key must match the DME.
Check all items before first startup: coolant system bleed (the M50 bleeds from the expansion tank, not the thermostat housing), clutch pedal travel, and engine bay wiring routing. Allow two to three weekends for a first-time swap in a clean shell with all parts on hand.