BMW M50

BMW M50 engine
Overview
Manufacturer	BMW
Production	1991–1996
Body and chassis
Class	Straight-6
Chronology
Predecessor	BMW M20
Successor	BMW M52

The BMW M50 is an I6 piston engine. It was introduced in 1990 to replace the BMW M20 in the new 3-series and was replaced by the BMW M52 in 1995. Displacement ranges from 2.0 L to 3.2 L. It is a DOHC 24-valve engine. A Technical Update or M50TU version from 1992 introduced VANOS variable valve timing.

The M50 was not related to the M20 though it used the same 91 mm cylinder spacing, bore, and stroke at 2.0 L and 2.5 L. Contrary to its successor, the BMW M52, the M50 has a gray iron engine block, which contributes to its long life expectancy and makes it immune to the corrosive properties of alternative fuels, like E85 ethanol. The rest of the engine is composed of an interesting material mix: the head gasket is made of aluminum alloy, the exhaust manifold consists of cast iron, and the intake manifold was made of plastics in a once revolutionary production process, which was first employed on a grand scale in the manufacture of the BMW M50 engine.

Models

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
M50B20	2.0 L (1991 cc/121 in³)	110 kW (150 hp) @ 6000	190 N·m (140 ft·lbf) @ 4700	6750	80mm	66mm	1991
M50TUB20		110 kW (150 hp) @ 5900	190 N·m (140 ft·lbf) @ 4200	6750	80mm	66mm	1993
M50B24	2.4 L	138 kW (188 hp) @ 5900	235 N·m (177 ft·lbf) @ 4700	6550	84mm	72mm	1991
M50B25	2.5 L (2494 cc/152 in³)	141 kW (192 hp) @ 6000	245 N·m (181 ft·lbf) @ 4700	6500	84mm	75mm	1991
M50TUB25		141 kW (192 hp) @ 5900	250 N·m (184 ft·lbf) @ 4200	6500	84mm	75mm	1993
S50B30	3.0 L (2990 cc/182 in³)	210 kW (286 hp) @ 7000	320 N·m (235 ft·lbf) @ 3600	7280	86mm	85.8mm	1992
S50B32	3.2 L (3201 cc/195 in³)	236 kW (321 hp) @ 7400	350 N·m (257 ft·lbf) @ 3250	7600	86.4mm	91mm	1995

M50B20

The 2.0 L (1991 cc) M50B20 was introduced with the 1991 520i. It has an 80 mm bore and 66 mm stroke and produces 150 hp (110 kW). From the '93 model year onwards, the engine received a 'technical update' which included the addition of VANOS (VAriable NOckenwellen Steuerung), BMW's variable valve timing system, on the intake cam. The engine thereafter became known as the M50TUB20.

Applications:

• 1991-1993 E36 320i
• 1991-1993 E34 520i

M50B24

This is a 2.4 L engine based on the 2.5 L M50B25, with a reduced stroke. This engine is only fitted to CKD kits assembled in Thailand. Power output is 188 hp (140 kW) and torque is 134 ft·lbf (235 Nm).

Applications:

• 1993-1997 E36 3-Series (Thai specification)
• 1993-1995 E34 5-Series (Thai specification)

M50B25

The 2.5 L (2494 cc) M50B25 was introduced with the 1991 525i/525ix . It has an 84 mm bore and 75 mm stroke and produces 192 PS (141 kW; 189 hp) @5900 rpm and 245 N·m (181 lb·ft) @4700 rpm.

Applications:

• 1991-1992 E34 525i/525ix
• 1992 E36 325i/325is

M50TUB20

The M50TUB20 is a technologically upgraded (TU) version of the BMW M50B20, introduced in 1993. The most notable change present is the inclusion of BMW's VANOS variable cam timing system on the intake cam. Power output remains identical; however, there is a slight increase in torque at lower and medium rpms.

Applications:

• 1993-1996 E34 520i
• 1993-1998 E36 320i

M50TUB25

The M50TUB25 is a technologically upgraded (TU) version of the BMW M50B25, introduced in 1993. The most notable change present is the inclusion of BMW's VANOS variable cam timing system on the intake cam. Power output remains identical; however, there is a slight increase in torque at lower and medium rpms 184 vs 181.

Applications:

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

S50B30

The S50B30 was a special sports-oriented 3.0 L version, which powered the RoW spec E36 M3. Power is 286 hp (210 kW). The S50B30 has a bore of 86 mm and a stroke of 85.8 mm, with a total displacement of 2990 cc. The engine has a maximum permissible speed of 7280 rpm +/-80, and a permissible constant speed of 7000 rpm. It used an Individual Throttle Body intake system with separate butterflies adjacent to each of the 6 inlet ports, an oversized MAF, and a tubular exhaust manifold. The cylinder head was unique and the VANOS system was more advanced than the one used on normal M50s.

Applications:

• 1992-1995 E36 M3

S50B32

The S50B32 was an evolution version of the S50B30. Power of the 3.2 L version is 317 hp (236 kW). Improvements over the previous 3.0l version include Dual Vanos operating on the exhaust camshaft as well as the inlet camshaft, increased compression ratio to 11.3:1, reduced valve stem thickness (and weight), and higher redline. This engine has a bore of 86.4 mm (3.4 in) and a stroke of 91.0 mm (3.6 in) giving a displacement of 3201 cc. It has a maximum permissible speed of 7600 +/-50 rpm, and a permissible constant speed of 7400 rpm. Power output was rated at 321 PS (236 kW; 317 hp) at 7400 rpm, with a torque rating of 258 lb⋅ft (350 N⋅m) at 3275 rpm.

Applications:

• 1996-1999 E36 M3 (except for the U.S.)
• 1997-2000 M Roadster (except for the U.S.)
• 1998-2000 M Coupe (except for the U.S.)