BMW S38

1988–1992 S38B36 in an E34 M5

The BMW S38 is a straight-6 DOHC piston engine which replaced the M88 and was produced from 1986-1996. It is based on the M88/3 engine.^[1] This engine is similar to the M30, but has a 24-valve cylinder head, duplex timing chain, dual overhead cam layout and shim and bucket style valvetrain. In addition to the top end revisions, the S38 also had six individual throttle bodies and intake trumpets fed by a cast aluminum intake plenum.

Models

Engine	Displacement	Power	Torque	Bore	Stroke	Year	Application
S38B35	3,453 cc (211 cu in)	252 hp (188 kW) @ 6500 rpm	330 N·m (243 lb·ft) @ 4500 rpm	93.4 mm (3.7 in)	84 mm (3.3 in)	1986–1988	BMW E28 M5 (NA spec), BMW M6 (NA spec), BMW M635CSi with catalytic converter
S38B36	3,535 cc (216 cu in)	315 hp (235 kW) @ 6900 rpm	360 N·m (266 lb·ft) @ 4750 rpm	93.4 mm (3.7 in)	86 mm (3.4 in)	1989–1993	BMW E34 M5 (NA spec) and Euro spec 1989–1992
S38B38	3,795 cc (232 cu in)	340 hp (250 kW) @ 6900 rpm	400 N·m (295 lb·ft) @ 4750 rpm	94.6 mm (3.7 in)	90 mm (3.5 in)	1992–1996	BMW E34 M5

S38B35

The S38B35 was based on the M88/3, but with changes including a dual-row timing chain, camshaft, compression ratio lowered to 9.8:1 and fitted with a catalytic converter.^[2]

Applications:

• 1984-1988 BMW M5 (E28) sedan
• 1986-1989 E24 BMW M6 coupe
• 1987-1989 E24 M635CSi coupe^[3]

S38B36

For the S38B36 displacement was enlarged from 3453 to 3535 cc,^[3] achieved by increasing the stroke from 84mm to 86mm^[1] by using a longer forged steel crankshaft. Different camshafts were also used and the compression ratio was increased to 10:1. A variable-length inlet manifold was used claimed to improve torque output,^[1] equal length stainless steel exhaust headers remains.^[4] The fuel injection system was Bosch Motronic.

Applications:

• 1988-1992 E34 M5 sedan

S38B38

In 1992, BMW further enlarged the S38 engine to 3795 cc, with power climbing to 250 kW (340 hp) and torque increasing to 400 N·m (300 lb·ft).^[3] Coil-on-plug ignition replaced the traditional distributor which was used on previous S38 engines and the Bosch Motronic 3.3 fuel injection system was used.^[1] Other upgrades include:

• The resonance flap now is controlled by the DME.
• Also gains a new spot on the power curve for the above, at 2,480 rpm (the other two being at 4,120 rpm and 6,720 rpm)
• Thus it develops ~ 80% of its total torque from just ~ 1,800 rpm.
• A new dual mass flywheel that acts like a harmonic balancer.
• New design for the front crankshaft damper with four stretch bolts which are fastened with three phases.
• The compression ratio has been raised from 10.0:1 to 10.5:1
• The exhaust manifold specially developed from a high grade superalloy family, named inconel^[5] that is used in extreme environments and high temperature applications such as Formula One and NASCAR exhaust systems and space shuttle programs.

This engine was used in the E34 M5 until finished production in 1996.

Applications:

• 1992-1996 European-spec BMW M5 (E34)

References

1. http://www.usautoparts.net/bmw/engines/s38.htm
2. http://www.bmwmregistry.com/model_faq.php?id=7
3. http://www.bmwheaven.com/database/engine.php?type=Motorsport
4. http://bmwfans.info/parts/catalog/E34/Sedan/USA/M5_3.6-S38/LHD/M/1990/march/browse/engine/exhaust_manifold/
5. Inconel

External links

• The UnixNerd's BMW S38 engine page with photos, history and common problems.