The BMW M50 is a

straight-6 The straight-six engine (also referred to as an inline-six engine; abbreviated I6 or L6) is a piston engine with six cylinders arranged in a straight line along the crankshaft. A straight-six engine has perfect primary and secondary engine bala ...

DOHC An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion cha ...

petrol engine which was produced from 1990 to 1996. It was released in the E34 520i and 525i, to replace the M20 engine. In September 1992, the M50 was upgraded to the M50TU ("technical update"), which was BMW's first engine to use

variable valve timing In internal combustion engines, variable valve timing (VVT) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with var ...

. Called single VANOS by BMW, the system adjusted the phasing of the intake

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 ...

. The M50 began to be phased out following the introduction of the M52 engine in 1994. The

E36 M3 The BMW M3 is a high-performance version of the BMW 3 Series, developed by BMW's in-house motorsport division, BMW M GmbH. M3 models have been produced for every generation of 3 Series since the E30 M3 was introduced in 1986. The initial mode ...

is powered by the S50 engine series, which is a high output version of the M50.

Design

A significant advance over its M20 predecessor, the M50 features dual overhead camshaft (DOHC) with four valves per cylinder (the M20 has a single overhead camshaft with 2 valves per cylinder),

coil-on-plug ignition A distributor is an enclosed rotating switch used in spark-ignition internal combustion engines that have mechanically timed ignition. The distributor's main function is to route high voltage current from the ignition coil to the spark plug ...

, a knock sensor and a lightweight plastic

intake manifold In automotive engineering, an inlet manifold or intake manifold (in American English) is the part of an engine that supplies the fuel/air mixture to the cylinders. The word ''manifold'' comes from the Old English word ''manigfeald'' (from the ...

. Both engines use an iron block with an aluminum alloy head. The redline is 6,500 rpm for the M50B25 and 6,750 rpm for the M50B20 (7,000 rpm for S50 models), the same as the final version of the M20. The location of the oil pan (sump) varies according to the model the M50 is installed in. It is in the front on the E34 5 Series (like the M20), whereas it is in the rear on the E36 3 Series.

Models

M50B20

BMW M50 engine in BMW-Museum in Munich, Bayern

The M50B20 was introduced with the 1990 520i. It has a bore of , 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 and produces . The compression ratio is 10.5:1. Applications: * 1990-1992 E34 520i * 1991-1992 E36 320i

M50B20TU

The M50B20 was updated with single VANOS in 1992. Peak torque became available at 4,200 rpm. It produces at 5,900 rpm and at 4,200 rpm. The compression ratio was raised to 11.0:1. Applications: * 1992-1994 E36 320i * 1992-1996 E34 520i

M50B24TU

This is a engine used in the Thailand and Oceania markets. It is based on the M50B25TU with the

reduced to and produces at 5,900 rpm and at 4,200 rpm. The compression ratio is 10.5:1. Applications: * 1993-1995 E36 325iA/2.4 * 1992-1996 E34 525iA/2.4

M50B25

The M50B25 was introduced with the 1990 525i and 525ix. It has a bore of , a stroke of and produces at 6,000 rpm and at 4,700 rpm. The compression ratio is 10.0:1. Applications: * 1990-1992 E34 525i, 525ix * 1991-1992 E36 325i, 325is

M50B25TU

The M50B25 was updated with single VANOS in 1992, resulting in peak torque becoming available at 4,200 rpm. It produces at 5,900 rpm and at 4,200 rpm. The compression ratio was increased to 10.5:1. Applications: * 1993-1995 E36 325i, 325is * 1992-1996 E34 525i, 525ix

M50B30TU concept

In 1993, BMW Individual created an concept of BMW E34 530iX called Enduro Touring. Only one car was produced, having an up-sized variant of M50B25TU engine. Bore and stroke was increased and the total displacement of 3.0 was achieved. The power and torque both increased to and respectively.

S50

The S50 is the high performance version of the M50 which was used in the

, replacing the four-cylinder

BMW S14 The BMW S14 is a DOHC four-cylinder petrol engine which was used in the E30 M3, E30 320iS, and E36 320i Super Touring. It is based on the BMW M10 block and the cylinder head from the six-cylinder BMW S38 with two cylinders removed. The direct succ ...

engine used in the E30 M3. Like the M50, the S50 has an iron block and aluminum head with four valves per cylinder. In the United States, a less powerful engine called the "S50B30US" was used, which shares more in common with the regular M50 engine than the other S50 versions.

S50B30

The S50B30 was used in most countries, except for the United States (in 1993, BMW Canada officially imported 45 M3's with the S50B30 engine). The S50B30 produces , has a bore of , a stroke of and a compression ratio of 10.8:1. The redline is 7,200 rpm. The S50 has an individual

throttle body A throttle is the mechanism by which fluid flow is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle'' ...

for each cylinder, single-VANOS (variable valve timing on the intake camshaft), Bosch Motronic M3.3 engine management and redesigned intake and exhaust systems. The limited edition "M3 GT" model from 1995 produced . It had different

s and a redesigned sump and oil pump. Applications: * 1992-1995

(except for U.S.)

S50B30US

In the United States, the 1994-1995 model years of the

are powered by the S50B30US, a engine which produces . This engine is more closely related to the standard M50 engine and has the same compression ratio as the M50B25TU, but uses a different camshafts, crankshaft, connecting rods, and pistons. The bore is , the stroke is and the redline is 7,000 rpm. In 1996, the S50B30US was replaced by the

BMW S52 The BMW M52 is a straight-6 DOHC petrol engine which was produced from 1994 to 2000. It was released in the E36 320i, to replace the M50. The BMW S52 engine is a high performance variant of the M52 which powered the American and Canadian market E ...

engine (in the United States and Canada only). Applications: * 1994-1995

(U.S. only)

S50B32

In 1995, the S50B32 replaced the S50B30 (except in Canada and the United States, where the

engine was used instead). Power output increased to and the displacement increased to , due to an increased stroke of and a slight increase in bore to . The S50B32 has double-VANOS (variable valve timing on both camshafts) and a secondary oil pick-up was added. The compression ratio is 11.3:1 and the redline is 7,600 rpm. Engine management is the Siemens MSS50, with 3 knock sensors. Applications: * 1995-1999

(except Canada and the United States) * 1996-2000 Z3 M Coupe and M Roadster (except Canada and the United States)

References

{{BMW automotive petrol engines: 1980s to 2000s M50 Straight-six engines Gasoline engines by model