BMW M20

M20B20

Early M20 engine with K-Jetronic

The first models to use the M20 were the E12 520/6 and the E21 320/6, which used the 2.0 L M20B20.^[12][13] This engine uses a bore of 80 mm (3.1 in) and a stroke of 66 mm (2.6 in).^[12] The M20B20 initially used a Solex 4A1 four-barrel carburetor,^[14] had a compression ratio of 9.2:1 and a redline of 6,400 rpm.

The M20B20 first became fuel-injected in 1981,^[15] with Bosch K-Jetronic used.^[16] The compression ratio was raised to 9.9:1. In September 1982, the fuel injection was updated to LE-Jetronic (1982–1989) with a redline of 6,200 rpm. The engine was also updated for the E30 application (and E28) with a new big port 731 cylinder head, lighter block and new manifolds for Bosch LE Jetronic. The M60 designation was finally dropped and replaced with M20, and the 323i engine also gained the same updates and fitted too the new E30 model ^[17] In 1987, the M20B20 was again revised with the addition of Bosch Motronic engine management,^[18][17] a catalytic converter and a compression ratio of 8.8:1.

The M20B20 was not sold in North America.

Applications:

• 1976–1981 E12 520/6 (carburettor)
• 1977–1982 E21 320/6 (carburettor)
• 1981–1982 E28 520i (K-Jetronic)^[19]
• 1982–1984 E28 520i (L-Jetronic)^[20]
• 1982–1984 E30 320i (L-Jetronic)
• 1984–1987 E28 520i (LE-Jetronic)^[21]
• 1984–1987 E30 320i (LE-Jetronic)
• 1986–1987 E28 520i (Motronic)^[22]
• 1987–1992 E30 320i (Motronic)
• 1988–1990 E34 520i (Motronic)

M20B23

Six months after the M20 was launched with the carburetted M20B20, the larger, fuel-injected M20B23 was introduced for March 1978. The initial version of the M20B23 uses the same head (known as '200') and block as the carbureted 2.0 litre but a longer 76.8 mm (3.0 in) stroke crank. The bore is 80 mm (3.1 in). Fuel injection is K-Jetronic,^[14] the compression ratio is 9.5:1 and the redline is 6,400 rpm.

The E30 version used LE-Jetronic and the same improvements were used as per the E30 320i with the bigger port 731 head. and initially produced 139 bhp using a compression ratio of 9.8:1. In 1984, the fuel-injection, exhaust and camshaft were upgraded to LE-Jetronic and power increased to 110 kW (150 bhp) with a redline of 6,500 rpm.^[23]

The M20B23 was not sold in North America.

Applications:

• 1977–1982 E21 323i (K-Jetronic)^[24]
• 1982–1984 E30 323i (L-Jetronic)
• 1984–1987 E30 323i (LE-Jetronic)

M20B25

Engine block of an M20B25

In 1985, the M20B25 replaced the M20B23. The M20B25 has a capacity of 2.5 L and initially produced 130 kW (174 hp) (without a catalytic converter).^[25] The M20B25 head is known as "885" (since the casting number ends in 885), it has a bore of 84 mm (3.3 in), a stroke of 75 mm (3.0 in), a compression ratio of 9.7:1, a redline of 6,500 rpm and uses the Bosch Motronic 1.1 engine management system.^[26][17]

In 1987, the engine management was upgraded to Motronic 1.3,^[27][17] the compression ratio was reduced to 9.3:1 and power was reduced to 126 kW (169 bhp) for models without catalytic converters. Models with catalytic converters had a compression ratio of 8.8:1 and produced 125 kW (168 bhp).

Applications:

• 1985–1993 E30 325i
• 1989–1990 E34 525i
• 1988–1991 Z1

M20B27

The M20B27 was designed for efficiency (thus the e for the Greek letter eta in 325e) and low-rev torque.^[28] This is an unusual design strategy for a BMW straight-six engine, which are usually designed for power at high RPM. Compared with the M20B25, the stroke is increased from 75 mm (3.0 in) to 81 mm (3.2 in), resulting in a capacity of 2.7 litres.^[26] As per the M20B25, the bore is 84 mm (3.3 in). To reduce friction and improve efficiency, the M20B27 changes include using the '200' version of the head (which has smaller ports), a different camshaft, four camshaft journals and softer valve springs. Due to these changes the rev limit on the M20B27 was reduced to 4,800 rpm. A compression ratio of 9.0:1 was used on the US 528e, and 11:1 on Euro 525e and 325e cars - this was reduced to 10.3:1 in 1985.^[29] The initial M20B27 engines produces 123 hp (92 kW) and 177 lb⋅ft (240 N⋅m) at 3,250 rpm for models without a catalytic converter.^[26] Models with a catalytic converter produce 121 hp (90 kW) and 170 lb⋅ft (230 N⋅m).

The first car to use this engine was the US market 528e from 1982.

In late 1987, the fuel injection was upgraded from Motronic 1.0 to Motronic 1.3 on the US market plastic bumper 325e 'Super Eta',^[30][31] the cylinder head changed to the "885" version, the compression ratio was reduced to 8.5:1 and the redline increased to 5,200 rpm.^[32] Power output increased to 127 hp (95 kW) at 4,800 rpm.

In the early 1990s BMW South Africa used components from the Alpina C3 2.7 to produce an E30 specifically for Stannic Group N production car racing. The first iteration of this engine used in the E30 325iS produced 145 kW and the second revision, often referred to as "Evo2" or on the VIN plate as "HP2" produced 155 kW.

Applications:

• 1982–1987 E30 325e, 325e
• 1982–1988 E28 525e (called 528e in North America)
• 1989–1992 E30 325iS (Only available in South Africa)