Available from 1986 to 1996, the BMW S38 was an inline six-cylinder petrol engine that was developed and built by BMW’s ‘M’ division (BMW M GmbH).
The S38 engine replaced BMW’s M88 engine and was based on the M88/3 variant within that engine family. Compared to the M88/3 engine, the S38B36 engine had:
- Bigger bores for increased capacity;
- A new forged steel crankshaft which increased stroke;
- Duplex timing chains.
- Bigger intake valves and air filter housing; and,
- A three-way ceramic catalytic converter
S38B36
The S38B36 engine had a cast iron block, a cross-flow alloy cylinder head, a forged steel crankshaft, double overhead camshafts (DOHC, duplex chain driven), four valves per cylinder and a compression ratio of 10.0:1. Furthermore, the S38B36 engine Bosch Motronic M 1.2 engine management and a hot wire air mass sensor.
The S38B36 engine also had an electronically-controlled butterfly valve in the intake plenum that would operate to improve torque at low engine speeds and power at higher engine speeds. Similar to a variable length intake manifold, the butterfly valve operated to vary the length of the induction tract when
- Engine speed was below 4120rpm and full throttle was applied; or
- Engine speed was above 6720rpm and full throttle was applied.
S38B38
Available from 1992, the S38B38 engine introduced the following changes:
- Coil-on-plug ignition (replacing the distributor of the S38B36);
- Bosch Motronic M 3.3 engine management;
- New aluminium alloy pistons and an increased compression ratio of 10.5:1 (from 10.0:1);
- The resonance flap was controlled by the engine management system (previously controlled by a separate unit) and could be operated at 2480rpm, in addition to the 4120rpm and 6720rpm engine speeds;
- Camshaft duration was changed to 264 degrees/108 degrees;
- Bigger inlet valves (38.5 mm, previously 37 mm) and sodium-filled exhaust valves (32.5 mm, previously 32 mm);
- Valve lift was increased to 10.7 mm for improved cylinder filling;
- A new dual mass flywheel was introduced which had a harmonic balancer with four stretch bolts;
- The exhaust manifold was produced from Inconel, a high grade super-alloy;
- The twelve crankshaft counterweights were rounded on one side to reduce the inertia of the crankshaft; and,
- A more compact and lighter Emitec metallic type catalytic converter with six monoliths replaced the ceramic catalytic converter.
Engine | Capacity | Peak power | Peak torque | C.R. | Models | Years |
---|---|---|---|---|---|---|
S38B36 | 3535 cc (93.5 x 86.0) |
232kW at 6900rpm | 360Nm at 4750rpm | 10.0:1 | E34 M5 | 1988-92 |
S38B38 | 3795 cc (94.6 x 90.0) |
250kW at 6900rpm | 400Nm at 4750rpm | 10.5:1 | E34 M5 | 1992-96 |