| BMW S38 engine | |
| Production: | 1984 - 1995 |
| Configuration: | Straight-6 |
| Displacement: | 3453cc 3535cc 3795cc |
| Bore: | 93.42NaN2 94.62NaN2 |
| Stroke: | 842NaN2 862NaN2 902NaN2 |
| Valvetrain: | DOHC |
| Fueltype: | Petrol |
| Block: | Cast iron |
| Head: | Aluminium |
| Predecessor: | BMW M88 |
| Successor: | None |
The BMW S38 is a straight-6 DOHC petrol engine which replaced the M88 and was produced from 1984–1995.[1] [2] 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.
The S38 is based on the M88/3 engine.[3] 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 duration.[4] As per the M88/3, the S38 uses a DOHC valvetrain with shim-and-bucket valve actuation.[5] Air intake is via six individual throttle bodies with intake trumpets, fed by a cast aluminum intake plenum.[6]
| Version | Displacement | Power | Torque | Years | |
|---|---|---|---|---|---|
| S38B35 | 34531NaN1 | 1900NaN0 at 6,500 rpm | 3300NaN0 at 4,500 rpm | 1986–1989 | |
| S38B36 | 35351NaN1 | 2320NaN0 at 6,900 rpm | 3600NaN0 at 4,750 rpm | 1989–1993 | |
| S38B38 | 37951NaN1 | 2500NaN0 at 6,900 rpm | 4000NaN0 at 4,750 rpm | 1991–1995 |
The initial version of the S38 has a bore of 93.41NaN1 and a stroke of 841NaN1.
Applications:
For the S38B36, the displacement was increased to 35350NaN0. This was achieved by increasing the stroke by 2mm to 862NaN2,[3] by using a new forged steel crankshaft.[8] 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[9] a hotwire mass airflow sensor (MAF) and Bosch Motronic engine management.
Applications:
In late 1991, BMW further enlarged the S38 engine to 37951NaN1, by increasing the bore to 94.62NaN2 and the stroke to 902NaN2.[10] Power increased to 2500NaN0 at 6,900 rpm and torque increased to 4000NaN0 at 4,750 rpm.[7]
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 flywheel, an exhaust manifold made of Inconel, larger intake and exhaust valves, lighter pistons, and the throttle bodies increasing by 4mm to 50mm.[8]
Applications: