BMW S38 explained

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.

Design

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]

Versions

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

S38B35

The initial version of the S38 has a bore of 93.41NaN1 and a stroke of 841NaN1.

Applications:

S38B36

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:

S38B38

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:

Notes and References

  1. Web site: BMW S38B35 car engine . bmw-grouparchiv.de . 17 June 2019.
  2. Web site: BMW S38B38 automotive engine . bmw-grouparchiv.de . 17 June 2019.
  3. Web site: BMW S38 engine. www.usautoparts.net. https://web.archive.org/web/20121118062944/http://www.usautoparts.net/bmw/engines/s38.htm. 18 November 2012.
  4. Web site: FAQ E28 M5. www.bmwmregistry.com. 16 September 2017.
  5. Web site: BMW S38 Valve adjustment tool. www.bigcoupe.com. 16 September 2017.
  6. Web site: BMW M88 and S38 M-Tech 24 Valve Six Cylinder Engines. www.unixnerd.co.uk. 14 September 2017.
  7. Web site: Information on Motorsport engines. www.bmwheaven.com. 14 September 2017.
  8. Web site: FAQ E34 M5. www.bmwmregistry.com. 16 September 2017.
  9. Web site: Exhaust manifold - M5 3.6 E34 Sedan USA S38. wwwbmwfans.info. 14 September 2017.
  10. Web site: 1994 BMW M5. Automobile-Catalog. 2018-12-08. Pawel. Zal.