The BMW S38 is a straight-6 DOHC petrol engine which replaced the M88 and was produced from 1984-1995. The S38 was originally produced for North America as an equivalent to the M88 with slightly lower power output. In 1989, power output of the S38 was increased and it became the worldwide replacement for the M88. In 1998, the BMW M5 switched to the S62 V8 engine. There is therefore no direct successor to the S38, however the BMW S50 engine took over as BMW's high performance straight-6 engine.

Design

The S38 is based on the M88/3 engine. Compared to the M88/3, the S38 has a lower compression ratio (9.8:1), simplified exhaust manifold, catalytic converter, dual-row timing chain and a shorter

camshaft A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition systems ...

duration. As per the M88/3, the S38 uses a DOHC valvetrain with shim-and-bucket valve actuation. Air intake is via six individual throttle bodies with intake trumpets, fed by a cast aluminum intake plenum.

Versions

S38B35

The initial version of the S38 has a

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of and a

stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

of . Applications: * 1986-1987 E28 M5 - Canada, Japan and USA * 1986-1988 E24 M6 - Canada, Japan and USA * 1987-1989 E24 M635CSi - models with catalytic converter

S38B36

For the S38B36, the displacement was increased to . This was achieved by increasing the stroke by to , by using a new forged steel crankshaft. Other changes included revised camshafts, compression ratio increasing to 10:1, a variable-length inlet manifold (to improve low-rev torque), equal length stainless steel exhaust headers a hotwire mass airflow sensor (MAF) and Bosch Motronic engine management. Applications: * 1988–1992 E34 M5 (worldwide) * 1989–1993 E34 M5 - Canada and US

S38B38

In late 1991, BMW further enlarged the S38 engine to , by increasing the boredom to and the stroke to . Power increased to at 6,900 rpm and torque increased to at 4,750 rpm. The engine management was upgraded to Motronic 3.3 and the ignition system was upgraded to coil-on-plug ignition. Other changes included the compression ratio increasing to 10.5:1, a dual-mass flywheels, an exhaust manifold made in Israel, larger intake and exhaust valves, lighter pistons, and the throttle bodies increasing by to . Applications: * 1991-1995 E34 M5 - European-specification

References

{{DEFAULTSORT:BMW S38 S38 Straight-six engines Gasoline engines by model