M20

M20B25 2.5 litre 12 Valve Engine

The M20 is an straight-6 piston engine of BMW.

The 12-valve, belt driven SOHC design was introduced in the 1977 BMW 520/6 and 320/6. With displacements ranging from 2.0 to 2.7 liters, it was the "little brother" to the larger BMW M30 engine. It was intended to replace the larger displacement 4-cylinder motors and was born out of BMW's conviction that a small six had more development potential than a large four (i.e. 2 liters+)

Powering the E21 and E30 3-Series, as well as E12, E28 and E34 5 Series cars, it was produced for nearly two decades, with the last examples powering the E30 325i touring built until sometime in 1993. By that time, the newer twin-cam M50 engines with 4 valves per cylinder had already been used in the E36 and E34 for a couple of years.

Three different head castings were used over the engine's production run. The earliest was #1264200 aka the "200". These were used in all e21 320/6 and 323i and e12 520/6 engines and later in the e28 and e30 eta engines (eta = "Power With Economy"). The next version was #1277731 aka the "731". This head was the same as the 200 but featured larger intake ports. The final version was #1705885 or "885" introduced in the 325i. Ports were further enlarged, valves were larger and the combustion chamber was redesigned to improve flow and thermodynamic efficiency.

As the BMW M21, it became a diesel engine that was also available with a turbocharger.

Engine Specs

Models

Engine	Displacement	Power	Torque	Redline	Year
M20B20	2.0 L (1990 cc/121 in³)	92 kW (123 hp) @ 5800	165 N·m (121 ft·lbf) @ 4000		1981
		92 kW (123 hp) @ 5800	170 N·m (125 ft·lbf) @ 4000		1981
		95 kW (127 hp) @ 6000	174 N·m (128 ft·lbf) @ 4000	6200	1985
		95 kW (129 hp) @ 6000	164 N·m (120 ft·lbf) @ 4300	6200	1986
M20B23	2.3 L (2316 cc/141 in³)	102 kW (143 hp) @ 5300	205 N·m (151 ft·lbf) @ 4000	6500	1982
		110 kW (139-150 hp) @ 6000	205 N·m (151 ft·lbf) @ 4000	6500	1983
M20B25	2.5 L (2494 cc/152 in³)	126 kW (168 hp) @ 5800	226 N·m (166 ft·lbf) @ 4000	6700	1985
		120 kW (170 hp) @ 5800	215 N·m (158 ft·lbf) @ 4000	6700	1985
		125 kW (168 hp) @ 5800	222 N·m (163 ft·lbf) @ 4300	6700	1987
M20B27	2.7 L (2693 cc/164 in³)	92 kW (121 hp) @ 4250	240 N·m (177 ft·lbf) @ 3250	4500	1983
		95 kW (127 hp) @ 4250	240 N·m (177 ft·lbf) @ 3250	4500	1986
		90 kW (120 hp) @ 4250	230 N·m (169 ft·lbf) @ 3250	4500	1985
		95 kW (127 hp) @ 4800	230 N·m (169 ft·lbf) @ 3200	4500	1986

Other variations

• M20b20
• M20b23