BMW M20

BMW M20 engine
Overview
Manufacturer	BMW
Production	1977–1993
Combustion chamber
Configuration	Straight-6
Displacement	2.0 L (1,990 cc/121 in³) 2.3 L (2,316 cc/141 in³) 2.5 L (2,494 cc/152 in³) 2.7 L (2,693 cc/164 in³)
Chronology
Predecessor	None
Successor	BMW M50

The BMW M20 was a straight-6 SOHC piston engine produced from 1977-1993. Like the larger capacity M30 engine it was produced alongside, the M20 has 12 valves. While the M30 camshaft is chain driven, the M20 camshaft and auxiliary shaft are driven by a timing belt. Initially released with a carburetor, later models used Bosch fuel injection.

History

With displacements ranging from 1990 cc to 2693 cc, it was the "little brother" to the larger BMW M30 engine. It has 91 mm (3.6 in) bore-spacing^[1] instead of 100 mm (3.9 in) of the M30.

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 April 1993.^[2] It was replaced by the DOHC BMW M50 engine.

Early versions of the M20 were sometimes referred to as the "M60",^[3] although the M60 code has since been used for a V8 engine first produced in 1992.

The M20 was the basis for the M21 diesel engine and the M70 V12 engine.^[4]

Models

M20B20

The first model to use the M20 was the E12 520/6, which used the 1991 cc M20B20.^[13] This engine uses a bore of 80 mm (3.1 in) and a stroke of 66 mm (2.6 in).^[13] Fuel was supplied by a Solex four-barrel carburetor.

The M20B20 first became fuel-injected in the 1982 520i,^[14] with Bosch L-Jetronic used. In 1987, the M20B20 was again revised with the addition of Bosch Motronic engine management^[15] and a catalytic converter.

Applications:

• 1977–1981 E12 520/6
• 1979–1983 E21 320/6
• 1982–1984 E28 520
• 1982–1988 E28 520i
• 1983–1992 E30 320i
• 1988–1990 E34 520i

M20B23

The M20B23 was used in 323i models, which were not sold in North America. The engine was first used in E21 323i^[16] and was replaced by the M20B25 in 1985.^[15]

The E30 version used L-Jetronic.^[17] and initially produced 102 kW (137 hp), followed up an increase to 110 kW (150 hp) in 1984.^[18] The 102 kW version continued to be available in certain markets with strict emissions regulations, such as Switzerland, until replaced by the 325i.^[9]

Applications:

• 1977–1982 E21 323i
• 1982–1985 E30 323i

M20B25

The M20B25 has a capacity of 2494 cc and initially produced 120 kW (160 hp) (or 126 kilowatts (169 hp) without a catalytic converter).^[18] 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 8.5:1 and used the Bosch Motronic 1.1/1.3 engine management system.^[19] In 1987, the M20B25 was upgraded to produce 125 kW (168 hp).^[18]

Applications:

• 1986–1993 E30 325i, 325iS, 325iC and 325iX
• 1989–1990 E34 525i
• 1988–1991 Z1

M20B27

The 2693 cc M20B27 was designed for efficiency (thus the e for the Greek letter eta in 325e) and low-rev torque.^[20] Compared with the M20B25, the stroke is increased from 75 mm (3.0 in) to 81 mm (3.2 in).^[19]

Power output is 121 hp (90 kW) at 4,250 rpm for M20B27 engines produced up until 1987 and 127 hp (95 kW) at 4,800 rpm for the "325es" model produced in 1988.^[19] Peak torque is 170 lb·ft (230 N·m) at 3,250 rpm for M20B27 engines. In 1987, the fuel injection was upgraded from Motronic 1.0 to Motronic 1.1/1.3.^[19]

Applications:

• 1982–1988 E30 325/325e/325es
• 1982–1988 E28 525e (or 528e in the US)

References

1. ↑ http://www.usautoparts.net/bmw/engines/m50.htm
2. ↑ http://www.autoevolution.com/cars/bmw-3-series-touring-e30-1986.html
3. ↑ http://www.bmwccbc.org/resources/index.html
4. ↑ http://www.usautoparts.net/bmw/engines/m21.htm
5. ↑ 5.0 5.1 Lösch, Annamaria, ed. (1981). World Cars 1981. Pelham, NY: The Automobile Club of Italy/Herald Books. p. 107. ISBN 0-910714-13-4. 
6. ↑ Büschi, Hans-Ulrich, ed. (March 10, 1983). "Automobil Revue '83" (in German and French) 78. Berne, Switzerland: Hallwag, AG. p. 204. ISBN 3-444-06065-3. 
7. ↑ Automobil Revue '83, p. 205
8. ↑ 8.0 8.1 8.2 8.3 8.4 Büschi, Hans-Ulrich, ed. (5 March 1987). Automobil Revue 1987 (in German and French) 82. Berne, Switzerland: Hallwag AG. pp. 184–186. ISBN 3-444-00458-3. 
9. ↑ 9.0 9.1 Büschi, Hans-Ulrich, ed. (March 1, 1984). "Automobil Revue '84" (in German and French) 79. Berne, Switzerland: Hallwag, AG. p. 179. ISBN 3-444-06070-X. 
10. ↑ Automobil Revue '83, p. 206
11. ↑ Heitz, Rudolf, ed. (1985-08-01). Auto Katalog 1986 (in German) 29. Stuttgart: Vereinigte Motor-Verlage GmbH & Co. KG. p. 210. 81530/85001. 
12. ↑ James M. Flammang (1994). Standard Catalog of Imported Cars, 1946-1990. Iola, WI: Krause Publications, Inc. pp. 125–126. ISBN 0-87341-158-7. 
13. ↑ 13.0 13.1 http://www.carfolio.com/specifications/models/car/?car=119361
14. ↑ http://www.automobile-catalog.com/car/1982/262835/bmw_520i_4-speed.html
15. ↑ 15.0 15.1 http://www.e30club.com/bmw-e30
16. ↑ http://www.bmwheaven.com/database/show.php?id=133
17. ↑ http://www.automobile-catalog.com/car/1985/265070/bmw_323i_sport_gearbox.html
18. ↑ 18.0 18.1 18.2 http://www.bmwheaven.com/database/engine.php?type=M20
19. ↑ 19.0 19.1 19.2 19.3 http://e30world.com/specifications/BMW-E30-specs-table
20. ↑ http://www.e30info.com/pages/diff.htm

External links

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