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BMW M20

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BMW M20 engine
Overview
Production1977–1993
Layout
ConfigurationStraight-6
Displacement2.0 L (1,991 cc)
2.3 L (2,316 cc)
2.5 L (2,494 cc)
2.7 L (2,693 cc)
Cylinder bore80 mm (3.15 in)
84 mm (3.31 in)
Piston stroke66 mm (2.60 in)
75 mm (2.95 in)
76.8 mm (3.02 in)
81 mm (3.19 in)
Cylinder block materialCast iron
Cylinder head materialCast aluminum alloy
ValvetrainSOHC
Combustion
Fuel typePetrol
Chronology
PredecessorNone
SuccessorBMW M50

The BMW M20 is a SOHC straight-six petrol engine which was produced from 1977 to 1993. It was introduced eight years after the larger BMW M30 straight-six engine, which remained in production alongside the M20.[1]

The first BMW models to use the M20 were the E12 5 Series and the E21 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 the M50 engine in 1990. The final M20 engines were fitted to the E30 3 Series touring and convertible model built in April 1993.[3]

The M20 was the basis for the BMW M21 diesel engine.[4] It is also loosely related to the BMW M70 V12 petrol engine.

History

[edit]

By the 1970s, BMW saw a need for a new I6 engine to bridge the displacement gap between their smaller M10 I4 and the M30 I6 engines.[5]: 92  This new engine would solve the following business- and engineering-related issues:

  1. The M30, despite being a turbine-smooth inline-6, was too large and too heavy to fit in the 3 Series engine bay.
  2. The M10, despite being a small and light inline-4, became too buzzy and unrefined at larger displacements; 2.0 L is typically an upper limit for inline-4 engines in terms of maintaining refinement.
  3. A 2.0 L variant of this new I6 would offer European buyers refinement and the turbine-like smoothness of an I6 while bypassing European displacement taxes.
  4. The new engine could be evolved to accommodate the tightening emissions standards of the 1970s and 1980s.

BMW debuted the M20 engine at the 1977 IAA in two forms: a 2.0 L variant with Solex 4A1 carburetor making 90 kW and a 2.3 L variant with Bosch K-Jetronic MPFI making 105 kW; both variants had a 80 mm bore.[6] In 1982 BMW increased the bore to 84mm, ultimately leading to 2.5 L and 2.7 L variants. The M20 was used in the E12 5 Series, E21 3 Series, E28 5 Series, E30 3 Series and E34 5 Series.

Early versions of the M20 were sometimes referred to as the "M60",[7][8] although the M60 designation has since been re-used for a V8 engine produced from 1992 to 1996.

Design

[edit]

The M20 shares the following design characteristics with the M10 and M30: [9][10]

  • The engine block is a closed deck design that is made out of cast iron and features siamesed cylinder bores
  • The cylinder head is a cross-flow design made out of cast aluminum alloy
  • The valvetrain layout is SOHC with 2 valves per cylinder. Rocker arms with manually adjustable eccentric pushers actuate the valves

The M20 differs from the M10 and M30 in the following ways:

  • The camshaft is driven using timing belt instead of a timing chain to reduce noise and production costs [11]
  • The bore spacing is reduced from 100 mm (3.9 in) to 91 mm (3.6 in) to reduce engine length and weight [12]
  • The slant angle is reduced from 30 degrees to 20 degrees when mounting the engine in the engine bay, resulting in a more upright engine [13]

Throughout the M20's production run, three different cylinder head casting variants were used: [14]

  • 1264200 (200): this variant was used for pre-1983 M20B20 and M20B23 engines, as well as in the pre-1988 M20B27 engine. This casting features very small intake ports with 40mm intake and 34 mm exhaust valves.
  • 1277731 (731): this variant was used for post-1982 M20B20 and M20B23 engines. It keeps the same valve diameters as the 200 casting but enlarges the intake ports.
  • 1705885 (885): this variant was used for the M20B25 and the 1988 M20B27 engines. This casting features the largest intake ports. The intake and exhaust valve diameters are both enlarged by 2 mm each over the 200 and 731 castings.

Variants

[edit]
VersionDisplacementPowerTorque Bore Stroke Compression RatioYearsNotes
M20B20 1,991 cc (121.5 cu in)90 kW (122 PS; 121 hp)
at 6,000 rpm[15]		163 N⋅m (120 lb⋅ft)
at 4,000 rpm		 80 mm (3.15 in) 66 mm (2.60 in) 9.2:11977-1982Solex 4A1 variant
92 kW (125 PS; 123 bhp)
at 5,800 rpm		170 N⋅m (125 lb⋅ft)
at 4,000 rpm		 9.0:1 (catalyst)

9.8:1 (non-catalyst)

 1982-1984 L-Jetronic fuel injection with "200" head
174 N⋅m (128 lb⋅ft)
at 4,000 rpm		1984-1987LE-Jetronic fuel injection with "731" head
95 kW (129 PS; 127 bhp)
at 6,000 rpm		164 N⋅m (121 lb⋅ft)
at 4,300 rpm		 8.8:11986-1992Motronic 1.1/1.3 engine management

Compression ratio reduced to accommodate emissions controls and unleaded gasoline

M20B23 2,316 cc (141.3 cu in)105 kW (143 PS; 141 bhp)
at 5,300 rpm[15]		190 N⋅m (140 lb⋅ft)
at 4,500 rpm		 76.8 mm (3.02 in) 9.5:11977-1982K-Jetronic fuel injection
102 kW (139 PS; 137 bhp)
at 5,300 rpm		205 N⋅m (151 lb⋅ft)
at 4,000 rpm		 9.0:1 (catalyst)

9.8:1 (non-catalyst)

 1982-1983 L-Jetronic
110 kW (150 PS; 148 bhp)
at 6,000 rpm		1983-1987LE-Jetronic
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		 84 mm (3.31 in) 75 mm (2.95 in) 9.4:11985-1990For markets that did not require a catalytic converter
125 kW (170 PS; 168 hp)
at 5,800 rpm		226 N⋅m (167 lb⋅ft)
at 4,300 rpm		 8.8:11987-1993For markets that required a catalytic converter
M20B27 2,693 cc (164.3 cu in) 90 kW (122 PS; 121 hp)
at 4,250 rpm		230 N⋅m (170 lb⋅ft)
at 3,250 rpm		 81 mm (3.19 in) 9.0:11982-1987For markets that required a catalytic converter
92 kW (125 PS; 123 hp)
at 4,250 rpm		240 N⋅m (177 lb⋅ft)
at 3,250 rpm		 11.0:11982-1985For markets that did not require a catalytic converter

Early high compression variant

95 kW (129 PS; 127 hp)
at 4,250 rpm		240 N⋅m (177 lb⋅ft)
at 3,250 rpm		 10.2:11985-1987For markets that did not require a catalytic converter

Compression ratio reduced to mitigate knocking

95 kW (129 PS; 127 hp)
at 4,800 rpm		 240 N⋅m (177 lb⋅ft)
at 3,200 rpm		 8.5:1 1988 "Super" Eta engine

Motronic 1.1

M20B20

[edit]
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 a 1,991 cc (121 cu in) version known as the M20B20VE or M60/2.[16][17] This engine uses a bore of 80 mm (3.15 in) and a stroke of 66 mm (2.60 in).[16] A Solex 4A1 four-barrel carburetor was used in the M20B20VE ("VE" is for vergaser- "carburettor" in German),[18] 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,[19] with Bosch K-Jetronic used in a 92 kW (123 hp) version called the M20B20KE.[20] 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 to LE-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 the M20B20LE.[21]

In 1987, the M20B20 was again revised with the addition of Bosch Motronic engine management, a catalytic converter and a compression ratio of 8.8:1.[22][21]

The M20B20 was not sold in the United States, but was available in the E30 (320i) in Canada.

Applications:

M20B23

[edit]

In March 1978 (six months after the M20 was launched), a fuel-injected and larger displacement version known as the M20B23KE (or M60/5) 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)[15] and the redline is 6,400 rpm.[18]

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 the M20B23LE 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.[27]

The M20B23 versions were not sold in North America.

Applications:

M20B25

[edit]

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 a catalytic converter).[29] 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 uses Bosch Motronic 1.1 engine management.[30][21]

In 1987, a catalyzed model with Motronic 1.3 engine management was introduced.[31][21] 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:

M20B27

[edit]

The M20B27 was designed for efficiency (thus the e for the Greek letter eta in 325e) and low-rev torque.[32] 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).[30] 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 the M20B27ME, produces 92 kW (123 hp) and 240 N⋅m (177 lb⋅ft) at 3,250 rpm for models without a catalytic converter.[30] Models with a catalytic converter produce 90 kW (121 hp) and 230 N⋅m (170 lb⋅ft).

In the United States, BMW's corporate 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.[33] 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, the M20B27ME.E version was introduced, increasing power output to 95 kW (127 hp) despite a lower compression ratio of 10.3:1.[34]

For the 1988 model year, the digital motor electronics was upgraded to Motronic 1.1 on the US market plastic bumper 325e and 528e 'Super Eta',[35][36] 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.[37] 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 the VIN plate as "HP2" produced 155 kW (208 hp).

Applications:

See also

[edit]

References

[edit]
  1. ↑ "BMW M30". www.bmw-tech.org. Retrieved 2 December 2017.
  2. ↑ "Engine Of The Day: BMW M20". www.jalopnik.com. 29 August 2009. Retrieved 18 September 2017.
  3. ↑ "BMW 3 Series Touring (E30) (1988 - 1993)". autoevolution.
  4. ↑ "Archived copy". Archived from the original on 2012-01-05. Retrieved 2012-06-05.{{cite web}}: CS1 maint: archived copy as title (link)
  5. ↑ Lewin, Tony (2016). The BMW Century. Motorbooks. ISBN 978-0-7603-5017-1.
  6. ↑ BMW AG (ed.): IAA Frankfurt/Main 15.9. bis 25.9.1977, p. 5, retrieved 17 September 2021
  7. ↑ "Useful info and resources". BMW Car Club of BC. Archived from the original on 2012-06-13.
  8. ↑ John G.Burns. "The UnixNerd's Domain - BMW M20 Six Cylinder Engines". Archived from the original on 2020-02-20. Retrieved 2021-02-01.
  9. ↑ "BMW M20B20 Engine". www.mywikimotors.com. Archived from the original on 2017-09-15. Retrieved 18 September 2017.
  10. ↑ Hans-Rüdiger Etzold: So wird’s gemacht (volume 68): BMW 5er Reihe 9/72 bis 7/81 (TYP E12), BMW 5er Reihe 7/81 bis 8/87 (TYP E28), Delius Klasing, Bielefeld, 1990, ISBN 978-3-7688-0666-4
  11. ↑ "M20 6-cylinder engine". www.usautoparts.net. Archived from the original on 2 May 2014.
  12. ↑ "M50 Engine". Archived from the original on 12 May 2012.
  13. ↑ "M50 Engine Technical Information (E36)". www.johnavis.com. Archived from the original on 2017-09-17. Retrieved 18 September 2017.
  14. ↑ "M20 - E30 Zone Wiki". www.e30zone.net. Retrieved 2026-09-09.
  15. 1 2 3 "BMW Presse: 47. IAA Frankfurt 1977". bmw-grouparchiv.de. Archived from the original on 18 September 2021. Retrieved 18 September 2021.
  16. 1 2 "1977 BMW 520".
  17. ↑ "BMW E21 3-series Sedan specs | Specs4BMW.com". Archived from the original on 2015-06-27. Retrieved 2015-12-21.
  18. 1 2 Lösch, Annamaria, ed. (1981). World Cars 1981. Pelham, NY: The Automobile Club of Italy/Herald Books. p. 107. ISBN 0-910714-13-4.
  19. ↑ "1982 BMW 520i 4-speed (for Europe) specs review". www.automobile-catalog.com.[permanent dead link]
  20. ↑ "Automobil Revue". 1983: 205. {{cite journal}}: Cite journal requires |journal= (help)
  21. 1 2 3 4 Büschi, Hans-Ulrich, ed. (March 5, 1987). Automobil Revue 1987 (in German and French). Vol. 82. Berne, Switzerland: Hallwag AG. pp. 184–186. ISBN 3-444-00458-3.
  22. ↑ "BMW e30 - BMW e30 Club". Archived from the original on 2011-11-26.
  23. ↑ "5' E28 520i FUEL INJECTION K-JETRONIC". www.realoem.com. Retrieved 21 September 2017.
  24. ↑ "5' E28 520i Control unit L-jetronic". www.realoem.com. Retrieved 21 September 2017.
  25. ↑ "5' E28 520i Control unit L-jetronic". www.realoem.com. Retrieved 21 September 2017.
  26. ↑ "5' E28 520i Uncoded DME control unit". www.realoem.com. Retrieved 21 September 2017.
  27. ↑ Büschi, Hans-Ulrich, ed. (March 1, 1984). Automobil Revue '84 (in German and French). Vol. 79. Berne, Switzerland: Hallwag, AG. p. 179. ISBN 3-444-06070-X.
  28. ↑ Ilir Dibrani. "BMW Heaven Specification Database - Specifications for BMW 323i E21 (1977-1982)". www.bmwheaven.com.
  29. ↑ Dibrani, Ilir. "BMW Heaven Specification Database - Engine specifications for M20 engines". www.bmwheaven.com.
  30. 1 2 3 "BMW E30 Specifications". www.e30world.com. Archived from the original on 24 February 2013.
  31. ↑ "3' E30 325i Uncoded DME control unit". www.realoem.com. Retrieved 21 September 2017.
  32. ↑ "BMW e30 1983-1991 differences between models". www.e30info.com.
  33. ↑ Heylen, Vic (1983-04-28). "BMW: Met de ETA op de zuinige tor" [BMW: With Eta on an economy run]. De AutoGids (in Dutch). Vol. 4, no. 94. Brussels, Belgium: Uitgeverij Auto-Magazine. p. 130.
  34. ↑ "M20B27 Engine Specs". www.e30tech.com. Archived from the original on 23 September 2017. Retrieved 21 September 2017.
  35. ↑ Automobil Revue '83, p. 206
  36. ↑ Heitz, Rudolf, ed. (1985-08-01). Auto Katalog 1986 (in German). Vol. 29. Stuttgart: Vereinigte Motor-Verlage GmbH & Co. KG. p. 210. 81530/85001.
  37. ↑ "325e". www.e30zone.net. Archived from the original on 23 September 2017. Retrieved 21 September 2017.
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