BMW S38 Engine (1988-96)

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.

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