BMW M20

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BMW M20 engine
M20B25.jpg
Overview
Production1977–1993
Layout
ConfigurationStraight-6
Block materialCast iron
Head materialAluminium
ValvetrainSOHC
Combustion
Fuel typePetrol
Chronology
PredecessorNone
SuccessorBMW M50

The BMW M20 is a straight-6 SOHC petrol engine produced from 1977 to 1993. It was introduced eight years after the larger BMW M30 straight-6 engine, which remained in production alongside the M20.[1]

The first models to use the M20 were the E12 520/6 and the E21 320/6. The initial M20 model had a displacement of 2.0 litres, with later versions having displacements of up to 2.7 litres.[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 325i touring model built in April 1993.[3]

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

History[edit]

By the 1970s, BMW felt the need for a smaller (than the M30) straight-6 engine for use in the 3 Series and 5 Series.[5](p92) The result was the 2.0 litre M20, BMW's smallest straight-6 engine of its day. With displacements ultimately ranging from 1991 cc to 2693 cc, it 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",[6][7] although BMW has since used the M60 code for a V8 engine produced from 1992-1996.

Design[edit]

As per the M30 engine, the M20 has an iron block, aluminium head and a SOHC valvetrain with 2 valves per cylinder.[8] The major differences to the M30 are:

  • A timing belt rather than a timing chain[9]
  • Bore spacing of 91 mm (3.6 in), rather than 100 mm (3.9 in)[10]
  • Slant angle of 20 degrees, compared with 30 degrees for the M30.[11]

Models[edit]

Engine Displacement Power Torque Years Fuel feed
M20B20 1,990 cc (121.4 cu in) 90 kW (121 bhp)
at 6,000 rpm
160 N⋅m (118 lb⋅ft)
at 4,000 rpm
1976-1982 carburettor
93 kW (125 bhp)
at 5,800 rpm
170 N⋅m (125 lb⋅ft)
at 4,000 rpm
1981-1982 K-Jetronic
92 kW (123 bhp)
at 5,800 rpm
170 N⋅m (125 lb⋅ft)
at 4,000 rpm
1982-1984 L-Jetronic
95 kW (127 bhp)
at 6,000 rpm
174 N⋅m (128 lb⋅ft)
at 4,000 rpm
1984-1987 LE-Jetronic
95 kW (127 bhp)
at 6,000 rpm
164 N⋅m (121 lb⋅ft)
at 4,300 rpm
1986-1992 Motronic
M20B23 2,316 cc (141.3 cu in) 105 kW (141 bhp)
at 5,300 rpm
190 N⋅m (140 lb⋅ft)
at 4,500 rpm
1977-1982 K-Jetronic
102 kW (137 bhp)
at 5,300 rpm
205 N⋅m (151 lb⋅ft)
at 4,000 rpm
1982-1984 L-Jetronic
110 kW (148 bhp)
at 6,000 rpm
205 N⋅m (151 lb⋅ft)
at 4,000 rpm
1984-1987 LE-Jetronic
M20B25 2,494 cc (152.2 cu in) 130 kW (174 bhp)
at 5,800 rpm
226 N⋅m (167 lb⋅ft)
at 4,000 rpm
1985-1987 Motronic 1.1
126 kW (169 bhp)
at 5,800 rpm
222 N⋅m (164 lb⋅ft)
at 4,300 rpm
1987-1991 Motronic 1.3
M20B27 2,693 cc (164.3 cu in) 92 kW (123 bhp)
at 4,250 rpm
240 N⋅m (177 lb⋅ft)
at 3,250 rpm
1982-1987 Motronic 1.1
95 kW (127 bhp)
at 4,250 rpm
240 N⋅m (177 lb⋅ft)
at 3,250 rpm
1987-1992 Motronic 1.3

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 the 1991 cc 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 to 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[edit]

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[edit]

Engine block of an M20B25

In 1985, the M20B25 replaced the M20B23. The M20B25 has a capacity of 2,494 cc (152.2 cu in) 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[edit]

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)

References[edit]

  1. ^ "BMW M30". www.bmw-tech.org. Retrieved 2 December 2017.
  2. ^ "Engine Of The Day: BMW M20". www.jalopnik.com. 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.
  5. ^ Lewin, Tony (2016). The BMW Century. ISBN 978 0 7603 5017 1.
  6. ^ "Useful info and resources". BMW Car Club of BC. Archived from the original on 2012-06-13.
  7. ^ John G.Burns. "The UnixNerd's Domain - BMW M20 Six Cylinder Engines".
  8. ^ "BMW M20B20 Engine". www.mywikimotors.com. Archived from the original on 2017-09-15. Retrieved 18 September 2017.
  9. ^ "M20 6-cylinder engine". www.usautoparts.net. Archived from the original on 2 May 2014.
  10. ^ "M50 Engine". Archived from the original on 12 May 2012.
  11. ^ "M50 Engine Technical Information (E36)". www.johnavis.com. Archived from the original on 2017-09-17. Retrieved 18 September 2017.
  12. ^ a b "1977 BMW 520".
  13. ^ "Archived copy". Archived from the original on 2015-06-27. Retrieved 2015-12-21.
  14. ^ a b Lösch, Annamaria, ed. (1981). World Cars 1981. Pelham, NY: The Automobile Club of Italy/Herald Books. p. 107. ISBN 0-910714-13-4.
  15. ^ "1982 BMW 520i 4-speed (for Europe ) specs review". www.automobile-catalog.com.
  16. ^ Automobil Revue '83, p. 205
  17. ^ a b c d Büschi, Hans-Ulrich, ed. (March 5, 1987). Automobil Revue 1987 (in German and French). 82. Berne, Switzerland: Hallwag AG. pp. 184–186. ISBN 3-444-00458-3.
  18. ^ "BMW e30 - BMW e30 Club". Archived from the original on 2011-11-26.
  19. ^ "5' E28 520i FUEL INJECTION K-JETRONIC". www.realoem.com. Retrieved 21 September 2017.
  20. ^ "5' E28 520i Control unit L-jetronic". www.realoem.com. Retrieved 21 September 2017.
  21. ^ "5' E28 520i Control unit L-jetronic". www.realoem.com. Retrieved 21 September 2017.
  22. ^ "5' E28 520i Uncoded DME control unit". www.realoem.com. Retrieved 21 September 2017.
  23. ^ Büschi, Hans-Ulrich, ed. (March 1, 1984). "Automobil Revue '84" (in German and French). 79. Berne, Switzerland: Hallwag, AG: 179. ISBN 3-444-06070-X.
  24. ^ Ilir Dibrani. "BMW Heaven Specification Database - Specifications for BMW 323i E21 (1977-1982)". www.bmwheaven.com.
  25. ^ Ilir Dibrani. "BMW Heaven Specification Database - Engine specifications for M20 engines". www.bmwheaven.com.
  26. ^ a b c "BMW E30 Specifications". www.e30world.com. Archived from the original on 24 February 2013.
  27. ^ "3' E30 325i Uncoded DME control unit". www.realoem.com. Retrieved 21 September 2017.
  28. ^ "BMW e30 1983-1991 differences between models". www.e30info.com.
  29. ^ "M20B27 Engine Specs". www.e30tech.com. Retrieved 21 September 2017.
  30. ^ Automobil Revue '83, p. 206
  31. ^ Heitz, Rudolf, ed. (1985-08-01). Auto Katalog 1986 (in German). 29. Stuttgart: Vereinigte Motor-Verlage GmbH & Co. KG. p. 210. 81530/85001.
  32. ^ "325e". www.e30zone.net. Retrieved 21 September 2017.