BMW M50

BMW M50 engine
Overview
Manufacturer	BMW
Production	1990–1996
Combustion chamber
Configuration	Straight-6
Chronology
Predecessor	BMW M20
Successor	BMW M52

The BMW M50 is a straight-6 DOHC piston engine was produced from 1990-1996. It was released in the E34 520i and 525i, to replace the M20 engine. It began to be phased out following the introduction of the M52 engine in 1994.

Compared with its M20 predecessor, the M50 features DOHC, 4 valves per cylinder, coil-on-plug ignition, a knock sensor and a lightweight plastic intake manifold.^[1] As per the M20, the M50 uses an iron block with an alloy head.^[2]

In September 1992, the M50 was upgraded to the M50TU ("technical update"), which added variable valve timing to the intake camshaft (called single VANOS by BMW).^[3]

The E36 M3 was powered by the S50 engine series, which a high output version of the M50.

Models

M50B20

The 1,991 cc (121 cu in) M50B20 was introduced with the 1990 520i. It has an 80 mm (3.1 in) bore and 66 mm (2.6 in) stroke and produces 110 kW (150 hp). Compression Ratio 10.5:1.^[4]

Applications:

• 1990-1992 E34 520i
• 1991-1992 E36 320i

M50B20TU

The M50B20 was updated with single VANOS in 1992. Compression Ratio raised to 11:1.^[4]

Applications:

• 1992-1994 E36 320i
• 1992-1996 E34 520i

M50B24

This is a 2.4 L engine used in the Thailand and Oceania markets.^[5] It is based on the 2.5 L M50B25 with a reduced stroke.

M50B25

The 2,494 cc (152 cu in) M50B25 was introduced with the 1990 525i and 525ix. It has an 84 mm (3.3 in) bore and 75 mm (3.0 in) stroke and produces 141 kW (189 hp) at 6000 rpm and 245 N·m (181 lb·ft) at 4700 rpm.^[4]

Applications:

• 1990-1992 E34 525i, 525ix
• 1991-1992 E36 325i, 325is

M50B25TU

The M50B20 was updated with single VANOS in 1992. Peak torque became available 500 rpm lower, at 4200 rpm.^[4]

Applications:

• 1993-1995 E36 325i, 325is
• 1992-1996 E34 525i, 525ix

S50

The S50 is the high performance version of the M50 which was used in the M3. Like the M50, it has an iron block and aluminum head with four valves per cylinder.

In the USA, 1994-1995 M3 models are powered by the "S50B30US"^[6][7] (which was replaced by the 3.2 S52 in 1996).^[8]

S50B30

The S50B30 is a 2,990 cc (182 cu in) higher output version of the M50 which powered the E36 M3, except in the USA. Canada had a limited production run of 45 cars with the S50B30 engine.

Engine management is provided by a Bosch Motronic M3.3 ECU with a separate "VNC" Vanos control unit providing fully variable single camshaft adjustment on the intake side. It produces 210 kW (282 hp),^[9] has a bore of 86 millimetres (3.4 in) and a stroke of 86 millimetres (3.4 in), and a compression ratio of 10.8:1.^[10] The limited edition "M3 GT" model from 1995 had different camshafts and a redesigned sump and oil pump, and produced 216 kW (290 hp).^[9]

Upgrades over the M50 include:

• Individual throttle plates for each cylinder
• Continuously variable "Vanos" valve timing.
• Lightweight pistons
• Graphite-coated connecting rods
• Larger inlet valves
• Redesigned equal length exhaust manifolds

Applications:

• 1992-1995 E36 M3 (except for USA)

S50B30US

USA versions of the 1994-1995 E36 M3 are powered by a 3.0L tuned version of the M50 which produces 179 kW (240 hp).^[9] This engine was based on the M50B25TU and uses the same compression ratio,^[9] but uses a different crankshaft, connecting rods, and pistons.

Applications:

• 1994-1995 E36 M3 (USA only)

S50B32

In 1996, the 3,201 cc (195 cu in) S50B32 replaced the S50B30 (except in Canada and USA, where the M52-based S52 engine was used instead).^[11] Engine management is provided by a Siemens MSS50 control unit featuring integrated Vanos control for both the intake and exhaust camshafts. The oil sump is a smaller capacity unit first seen on the M3GT and features a dual pick-up system to lower the risk of oil being forced away from a single pick-up point under cornering. This engine produces 236 kW (316 hp).^[12] The compression ratio is 11.3:1,^[13] the bore is 86.4 mm (3.4 in) and the stroke is 91 mm (3.6 in).^[14]

Applications:

• 1996-1999 E36 M3 (except Canada and USA)
• 1996-1999 Z3 M coupe and M roadster (except Canada and USA)

See also

• BMW engines
• BMW M20
• BMW M52

References