The North American E36 M3 engines, the S50B30US and S52B32, are close relatives of the M50 and M52 in the 325i and 328i. That shared base is what makes them popular swaps into non-M E36s. This guide covers what they are and the decisions that decide how hard the swap is.
TL;DR
| What: | Putting a US-spec M3 engine into a 325i or 328i. |
| Why: | 240 hp from a six-cylinder that shares most of its architecture with the M50/M52. |
| The big decision: | Matching the engine’s electronics generation (OBD1 or OBD2) to the car’s. |
| Difficulty: | 4/5 |
The engines
| S50B30US | S52B32 | |
|---|---|---|
| Displacement | 2,990 cc | 3,152 cc |
| Bore × stroke | 86.0 × 85.8 mm | 86.4 × 89.6 mm |
| Power | 240 hp | 240 hp |
| Torque | 305 Nm | 320 Nm |
| Block | Cast iron | Cast iron |
| Years | 1994–1995 | 1996–2000 |
| Closest relative | M50 | M52 (single VANOS) |
| Engine management (Bentley) | Bosch DME M3.3.1 (OBD1) | Siemens MS41.1 (OBD2) |
| Manual gearbox in the M3 (Bentley) | ZF S5D 310Z | ZF S5D 320Z |
These US engines are different from the European S50B30/S50B32, which are far more complex engines and a different swap altogether.
Match the electronics generation
| Swap | What it means |
|---|---|
| S50B30US into an OBD1 325i (M50) | Same electronics generation and the same DME family as an M50TU (Bosch M3.3.1). The closest to a like-for-like swap: use the S50’s own engine harness and DME. |
| S52B32 into an OBD2 328i (M52) | Same generation: Siemens MS41.1 on both. Use the S52’s harness and DME. The immobiliser (EWS) pairing between DME, module and keys has to be dealt with. |
| S52B32 into an OBD1 car | Mixing generations. Running an S52 on OBD1 electronics is a known enthusiast route, but it needs adapted sensors and wiring and, above all, a DME tune made for the engine. Follow a supplier’s documented conversion and tune rather than improvising. |
Whatever the combination, treat the immobiliser first. See the EWS guide.
Before it goes in
The donor engine is 25-plus years old. While it’s on a stand:
- Compression and leak-down test before buying, or at least before installing
- reseal it: oil pan, rear main seal, oil filter housing, valve cover
- reseal the VANOS (S52: Beisan’s single-VANOS kit; see the M52 single VANOS guide)
- refresh the cooling system: see the cooling system overhaul
- consider new crankshaft and camshaft sensors while they are easy to reach
Part numbers: look them up by the donor engine’s VIN on RealOEM.
Drivetrain
- Gearbox: the M3s used ZF five-speeds (S5D 310Z with the S50US, S5D 320Z with the S52). A 325i’s Getrag S5D 250G bolts to the engine, since the bolt pattern is shared, but it was never paired with this torque at the factory. See the gearbox guide.
- Driveshaft: the front section must match the gearbox make (Getrag or ZF).
- Clutch and flywheel: use parts matched to the engine and gearbox you end up with.
Exhaust, intake, cooling
- Use the M3’s exhaust manifolds and a matching downpipe and mid-pipe. On OBD2 cars, keep every oxygen sensor the system expects.
- The S52 accepts the same M50 intake manifold upgrade as the M52. See the M50 manifold guide.
- The cooling system needs to be in perfect condition; the radiator suitable for the car’s engine bay and the use.
After the swap
With roughly 50 hp more than a 325i, the brakes and suspension should match the engine. The registration inspection may also expect it.
