| BMW M20 engine | |
|---|---|
 | |
| Overview | |
| Production | 1977–1993 |
| Layout | |
| Configuration | Straight-6 |
| Displacement | 2.0 L (1,991 cc) 2.3 L (2,316 cc) 2.5 L (2,494 cc) 2.7 L (2,693 cc) |
| Cylinder bore | 80 mm (3.15 in) 84 mm (3.31 in) |
| Piston stroke | 66 mm (2.60 in) 75 mm (2.95 in) 76.8 mm (3.02 in) 81 mm (3.19 in) |
| Cylinder block material | Cast iron |
| Cylinder head material | Aluminium |
| Valvetrain | SOHC |
| Combustion | |
| Fuel type | Petrol |
| Chronology | |
| Predecessor | None |
| Successor | BMW M50 |
TheBMW M20 is a SOHC straight-six petrol engine which was produced from 1977 to 1993. It was introduced eight years after the largerBMW M30 straight-six engine, which remained in production alongside the M20.[1]
The first cars to use the M20 were theE12 5 Series and theE21 3 Series. The initial M20 model had a displacement of 2.0 L (122 cu in), with later versions having displacements of up to 2.7 L (165 cu in).[2]
The M20 began to be phased out following the introduction of theM50 engine in 1990. The final M20 engines were fitted to theE30 3 Series wagon (estate) and convertible model built in April 1993.[3]
The M20 was the basis for theBMW M21 diesel engine.[4] It is also loosely related to theBMW M70 V12 petrol engine.
By the 1970s, BMW felt the need for a six-cylinder engine smaller than theBMW M30, to use in the 3 Series and 5 Series.[5]: 92 The resulting M20 had a displacement of 2.0 L (122 cu in), BMW's smallest straight-six engine of its day. BMW presented the M20 engine at the1977 IAA as a 90 kW 2.0-litre Solex 4A1carburetted version, and as a 105 kW 2.3-litre K-Jetronicmulti-point injected version.[6] Later versions had displacements up to 2.7 L (165 cu in). The M20 was used in theE12 5 Series,E21 3 Series,E28 5 Series,E30 3 Series andE34 5 Series.
Early versions of the M20 were sometimes referred to as the "M60",[7][8] although theM60 designation has since been re-used for aV8 engine produced from 1992 to 1996.
As per the M30, the M20 has an iron block, aluminium head and a SOHC valvetrain with 2 valves per cylinder.[9] It has a traditional rocker arm design and no hydraulic tappets.[10] The major differences to the M30 are:
| Version | Displacement | Power | Torque | Years | Notes |
|---|---|---|---|---|---|
| M20B20 | 1,991 cc (121.5 cu in) | 90 kW (122 PS; 121 bhp) at 6,000 rpm[14] | 163 N⋅m (120 lb⋅ft) at 4,000 rpm | 1977-1982 | Austrian models rated at 88 kW (120 PS)[15] |
| 92 kW (125 PS; 123 bhp) at 5,800 rpm | 170 N⋅m (125 lb⋅ft) at 4,000 rpm | 1982-1984 | |||
| 174 N⋅m (128 lb⋅ft) at 4,000 rpm | 1984-1987 | ||||
| 95 kW (129 PS; 127 bhp) at 6,000 rpm | 164 N⋅m (121 lb⋅ft) at 4,300 rpm | 1986-1992 | |||
| M20B23 | 2,316 cc (141.3 cu in) | 105 kW (143 PS; 141 bhp) at 5,300 rpm[14] | 190 N⋅m (140 lb⋅ft) at 4,500 rpm | 1977-1982 | |
| 102 kW (139 PS; 137 bhp) at 5,300 rpm | 205 N⋅m (151 lb⋅ft) at 4,000 rpm | 1982-1983 | |||
| 110 kW (150 PS; 148 bhp) at 6,000 rpm | 1983-1987 | ||||
| M20B25 | 2,494 cc (152.2 cu in) | 126 kW (171 PS; 169 bhp) at 5,800 rpm | 226 N⋅m (167 lb⋅ft) at 4,000 rpm | 1985-1990 | |
| 125 kW (170 PS; 168 bhp) at 5,800 rpm | 226 N⋅m (167 lb⋅ft) at 4,300 rpm | 1987-1992 | Catalyzed | ||
| M20B27 | 2,693 cc (164.3 cu in) | 92 kW (125 PS; 123 bhp) at 4,250 rpm | 240 N⋅m (177 lb⋅ft) at 3,250 rpm | 1982-1985 | US models rated at 90 kW (121 hp) |
| 90 kW (122 PS; 121 bhp) at 4,250 rpm | 230 N⋅m (170 lb⋅ft) at 3,250 rpm | 1985-1987 | Austrian models rated at 88 kW (120 PS)[16][17] | ||
| 95 kW (129 PS; 127 bhp) at 4,250 rpm | 240 N⋅m (177 lb⋅ft) at 3,250 rpm | 1985-1988 |
The first models to use the M20 were the E12 520/6 and the E21 320/6, which used a 1,991 cc (121 cu in) version known as theM20B20VE orM60/2.[18][19] This engine uses abore of 80 mm (3.15 in) and astroke of 66 mm (2.60 in).[18] ASolex 4A1 four-barrel carburetor was used in the M20B20VE ("VE" is forvergaser- "carburettor" in German),[20] and it has a compression ratio of 9.2:1 and a redline of 6,400 rpm.
The M20 first became fuel-injected in 1981,[21] withBosch K-Jetronic used in a 92 kW (123 hp) version called theM20B20KE.[22] The compression ratio was raised to 9.9:1.
In September 1982 (coinciding with the release of the E30 3 Series), the fuel injection was updated toLE-Jetronic with a redline of 6,200 rpm. Other upgrades included a larger port (known as "731") cylinder head, a lighter block and new manifolds.[citation needed] The "M60" designation was dropped and this version was known as theM20B20LE.[23]
In 1987, the M20B20 was again revised with the addition ofBosch Motronic engine management, a catalytic converter and a compression ratio of 8.8:1.[24][23]
The M20B20 was not sold in the United States, but was available in the E30 (320i) in Canada.
Applications:
In March 1978 (six months after the M20 was launched), a fuel-injected and larger displacement version known as theM20B23KE (orM60/5) was introduced. This version uses the same head (known as "200") and block as the 2.0 litre version but a longer 76.8 mm (3.02 in) stroke crank. The bore is 80 mm (3.15 in) and it has a capacity of 2,316 cc (2.3 L). Fuel injection was K-Jetronic, the compression ratio is 9.5:1, the power output is 105 kW (143 PS; 141 hp)[14] and the redline is 6,400 rpm.[20]
The 1982 version used LE-Jetronic, the 731 cylinder head, a compression ratio of 9.8:1 and the other upgrades as the per the 2.0 litre version. This version is called theM20B23LE and has a power output of 102 kW (137 hp).
In September 1983, the M20B23LE's fuel-injection, exhaust and camshaft were upgraded and power increased to 110 kW (148 hp) with a redline of 6,500 rpm. The 102 kW (137 hp) version continued to be available in certain markets with strict emissions regulations (such as Switzerland) until replaced by the 325i.[29]
The M20B23 versions were not sold in North America.
Applications:
In 1985, the M20B25 replaced the M20B23. The M20B25 has a capacity of 2,494 cc (152.2 cu in) and initially produced 126 kW (171 PS; 169 hp) (without acatalytic converter).[31] It has an upgraded cylinder head (known as "885"), a bore of 84 mm (3.31 in), a stroke of 75 mm (2.95 in), a compression ratio of 9.4:1, a redline of 6,500 rpm and usesBosch Motronic 1.1 engine management.[32][23]
In 1987, a catalyzed model with Motronic 1.3 engine management was introduced.[33][23] The compression ratio was reduced to 8.8:1 but thanks to the more sophisticated electronics power remained nearly as before, at 125 kW (170 PS; 168 hp). The uncatalyzed engine was kept in production for Southern Europe and other markets where unleaded petrol was not regularly available.
Applications:
The M20B27 was designed for efficiency (thus thee for the Greek lettereta in325e) and low-rev torque.[34] 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 to 81 mm (2.95 to 3.19 in), resulting in a capacity of 2,693 cc (164.3 cu in).[32] Since many markets tax cars based on engine displacement, the eta's larger displacement meant that it was not suitable for all markets. It was expressly developed with the American market in mind. As per the M20B25, the bore is 84 mm (3.31 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. The initial version, called theM20B27ME, produces 92 kW (123 hp) and 240 N⋅m (177 lb⋅ft) at 3,250 rpm for models without a catalytic converter.[32] Models with a catalytic converter produce 90 kW (121 hp) and 230 N⋅m (170 lb⋅ft).
In the United States, BMW'scorporate average fuel economy was at risk of not meeting requirements by 1984, primarily due to higher sales of their bigger, more expensive cars in the early 1980s.[35] The first car to use the M20B27 was the US market 528e in 1982. The compression ratio of the U.S. M20B27ME version was 9.0:1, compared with for cars sold elsewhere 11.0:1.
In 1985, theM20B27ME.E version was introduced, increasing power output to 95 kW (127 hp) despite a lower compression ratio of 10.3:1.[36]
In late 1987, the fuel injection was upgraded to Motronic 1.3 on the US market plastic bumper 325e and 528e 'Super Eta',[37][38] 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.[39] Power output increased to 95 kW (127 hp) 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 (194 hp) and the second revision, often referred to as "Evo2" or on theVIN plate as "HP2" produced 155 kW (208 hp).
Applications:
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