The BMW M21 is a six-cylinder-inline-diesel engine developed by BMW. The engine with swirl chamber injection is based on the otto engine M20 and was produced for BMW by the upper Austrian Steyr engine plant from 1983 to 1991. It was succeeded by the M51.
In the 1970s BMW decided to develop an engine, which would both be powerful and have a good fuel economy. This was caused by the oil crisis in 1973. In 1975 a group of BMW engineers started working on the M21 diesel engine, the otto engine M20 was taken as the basis. In 1983 at the IAA, the first passenger car was shown to the public which made use of the 85 kW M21. It was the E28 524td, which has a top speed of 180 km/h and reaches 100 km/h in 12,9 s. This 5er-BMW was the fastest series production diesel car in the world back in 1983. It has a fuel economy of 7,1 l /100 km.
Cylinder block alloy
Garret (85 kW engines only)
Swirl chamber injection
63 – 85 kW
152 – 220 Nm
The M21 is a water-cooled and swirl-chamber-injected six-cylinder-inline-diesel-engine with a cast iron block and OHC valvetrain. The camshaft is driven by a belt,each cylinder has one inlet and one outlet valve. Compared to the otto engine M20, the M21 has reinforced connecting-rods, cylinder heads, pistons, valves and a reinforced crankshaft with seven bearings.
For faster engine startup the M21 has a glowplug system called instant start, which reduces the time to reach starting temperature compared to similar diesel engines. The fuel is injected into swirl chambers.
A Garret turbocharger is used (without an intercooler). Initially, the M21 was only available as a turbocharged engine. In 1985, BMW introduced a naturally aspirated version of the M21, which was popular in countries with a high motor vehicle tax.
Initially, the fuel injection system was controlled mechanically. In 1987, this system was replaced by an electronic diesel control system,which increased the torque output by 10 N·m (7 lb·ft). The updated engine has a smaller turbocharger, which improves response.
85 kW (114 hp) at 4800 min−1
210 N·m (155 lb·ft) at 2400 min−1
220 N·m (162 lb·ft) at 2400 min−1
63 kW (84 hp) at 4600 min−1
152 N·m (112 lb·ft) at 2500 min−1
1983 - 1988 E28 524td
1985 - 1988 E28 524d (naturally aspirated)
1985 - 1993 E30 324d (naturally aspirated)
1985 - 1993 E30 324td
1988 – 1991 E34 524td
1984 - 1985 Lincoln Continental Mark VII
1984 - 1985 Lincoln Continental
1986 - 1987 Vixen 21 TD and Vixen 21 XC
1989 - 1991 Bertone Freeclimber
1992 UMM Alter II (Very rare UMM model, only 4 were made)