In 1986 BMW chose the
S38 designation for the catalyst
version of the famous M88/3 engine. The code S38 designates: (1) 'S' means
that the engine is originated by
BMW Motorsport, (2) the '3'
means that it is derived from the M30 engine family,
and (3) the '8' is chosen to make a reference to the legendary M88 motor.
Three different versions of the S38 were made by BMW M, and the most
powerful 3.8 liter engine was never officially exported to the USA.
3.5 liter Engine
To meet the US exhaust emission regulations of the
time, the catalyst equipped S38B35 replaced the M88/3. The S38B35 kept the
M88/3's bore, stroke and cylinder head, but the compression ratio decreased from 10.5:1 to 9.8:1
to install a catalytic converter. The
equally tuned exhaust headers of the M88/3 were replaced by log headers.
These changes had the effect of decreasing engine performance. The S38B35
delivered 260 hp and a torque of 330 nm (243 lb/ft) at 4500 rpm. Due to
additional factory options, the US E28 M5
and E24 M6 were noticeably heavier than the
European cars, and it had an impact on performance. The European E28 M5
can do the 0-100 km/h (0-62 mph) sprint in just 6.5 sec, while the US
version needs 0.3 sec more.
In the US and Japanese markets, the M635CSi was
renamed the M6, while Europe kept the M635CSi designation. The
distinguishing mark between the M6 and M635CSi is the engine, for the M6
always contains the S38B35 engine, while the M635CSi can have either the
S38B35 engine or the M88/3. Most of the E28 M5 and E24 M635CSi models in
Europe were equipped with the M88/3 engine, without the catalyst.
The production of the BMW
E28 5 Series ceased at the end of
1987, succeeded by the BMW E34. Soon after
the introduction of the E34, a Motorsport version became available, the
E34 M5. The engine that powered the E34
M5 is a further evolution of the S38B35 engine which powered the catalyst
versions of both the E28 M5 and E24 M635CSi.
The E24 M635CSi remained in production until the
Spring of 1989. During that time, the M88/3 and S38B35 engines were
produced by BMW Motorsport alongside the S38B36. This benefited the last
E24 M635CSI's because in their final production months, both the M88/3 and
S38B35 engines received the duplex timing chain of the S38B36.
3.6 liter Engine
To create the S38B36, the S38B35 engine was stroked from
84.0 mm to 86.0 mm, the same as the M30B35. This increased the displacement to 3535 cc.
The bore remained
The compression ratio was also
increased, from 9.8:1 to 10.0:1. The S38B36 delivered 315 hp @ 6900 rpm and
360 nm (269 lb/ft) at 4750 rpm.
The intake received an electronically controlled RAM
induction system to increase torque. A changeover valve was added to vary the
effective length of the induction system depending on load and engine
speed. The changeover valve operates when the engine speed is below
4120 rpm and full throttle or the engine speed is above 6720 rpm and full
throttle. The engine management system remained the Bosch Motronic, but
instead of measuring the airflow with a valve, the S38B36 received an
airflow measurement system based on a hot-wire sensor.
To meet emission requirements, a ceramic
catalytic converter was added to the exhaust system. An air injection feature for the exhaust
to control the emissions at cold-engine start up. Air
is injected into the exhaust system to convert
carbon monoxide into carbon dioxide, and hydrogen into water. Tropical regions
like the Middle East and Southeast Asia got a
slightly different version of the S38B36 with the
compression ratio reduced to 9.2:1.
3.8 liter Engine
In 1991, BMW Motorsport redesigned the
S38 to improve performance. The bore and stroke were increased again, and the displacement grew to 3795cc.
The compression ratio was increased to 10.5:1. The intake and exhaust
ports increased in size also, and each spark plug got it's own
high-voltage coil, eliminating the distributor rotor and the high-voltage wiring. A
smaller and lighter Emitec metallic
catalytic converter replaced the ceramic catalytic
converter. The main advantage of the Emitec metallic converter is that it
increases the flow of the exhaust gasses. The Bosch Motronic 1.2 fuel
management system was replaced with the Motronic 3.3 system. The new
system includes a resonance flap control. This feature
is the same as that used on the S38B36, but with an extra switch-point at 2480
The S38B38 was the last evolution within the S38
engine family. It delivered 347 hp @ 6900 rpm and 409 nm torque at 4750
These changes stretched the S38 to its limits (the
5.4 mm web spacing between
two cylinders is very narrow. This is 0.6 mm less than the
M49/3 racing engine.)
The S38B38 engine remained in production until the
summer of 1995 when the last of the E34 M5's left the production facility in Garching,
For the Swiss and Austrian markets, the S38B38's were
fitted with ceramic catalytic converters and smaller exhaust manifolds
(80mm vs. 90mm) from the S38B36 engine. As a result, the Austrian and Swiss
versions of the engine delivered 327 hp, not 347hp.