BMW M20

By the 1970s, BMW felt the need for a six-cylinder engine smaller than the BMW M30, to use in the 3 Series and 5 Series.{{cite book|last1=Lewin|first1=Tony|title=The BMW Century|date=2016|publisher=Motorbooks |isbn=978-0-7603-5017-1}}{{refpage|page=92}} The resulting M20 had a displacement of {{convert|2.0|L|cuin|0|abbr=on}}, BMW's smallest straight-six engine of its day. BMW presented the M20 engine at the 1977 IAA as a 90 kW 2.0-litre Solex 4A1 carburetted version, and as a 105 kW 2.3-litre K-Jetronic multi-point injected version.BMW AG (ed.): [https://bmw-grouparchiv.de/research/media/b758ee3b-59b1-4046-8a97-8355940ade0d/web IAA Frankfurt/Main 15.9. bis 25.9.1977], p. 5, retrieved 17 September 2021 Later versions had displacements up to {{convert|2.7|L|cuin|0|abbr=on}}. 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",{{cite web|url=https://www.bmwccbc.org/resources/index.html|title=Useful info and resources|publisher=BMW Car Club of BC|url-status=dead|archiveurl=https://web.archive.org/web/20120613171917/http://www.bmwccbc.org/resources/index.html|archivedate=2012-06-13}}{{cite web|url=https://www.unixnerd.demon.co.uk/m20.html|title=The UnixNerd's Domain - BMW M20 Six Cylinder Engines|author=John G.Burns|publisher=}} although the M60 designation has since been re-used for a V8 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.{{cite web|title=BMW M20B20 Engine|url=https://mywikimotors.com/m20b20/|website=www.mywikimotors.com|accessdate=18 September 2017|archive-url=https://web.archive.org/web/20170915064709/http://mywikimotors.com/m20b20/|archive-date=2017-09-15|url-status=dead}} It has a traditional rocker arm design and no hydraulic tappets.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 The major differences to the M30 are:

• A timing belt rather than a timing chain{{cite web|title=M20 6-cylinder engine|url=https://www.usautoparts.net/bmw/engines/m20.htm|website=www.usautoparts.net |url-status=dead |archiveurl=https://web.archive.org/web/20140502043709/http://www.usautoparts.net/bmw/engines/m20.htm|archivedate=2 May 2014}}
• Bore spacing of {{convert|91|mm|in|abbr=on}}, rather than {{Convert|100|mm|in|abbr=on}}{{cite web|url=https://www.usautoparts.net/bmw/engines/m50.htm |title=M50 Engine |url-status=dead |archiveurl=https://web.archive.org/web/20120512014705/http://www.usautoparts.net/bmw/engines/m50.htm |archivedate=12 May 2012 }}
• Slant angle of 20 degrees, compared with 30 degrees for the M30.{{cite web|title=M50 Engine Technical Information (E36)|url=https://bmw3series.johnavis.com/blog/654/m50-engine-e36/|website=www.johnavis.com|accessdate=18 September 2017|archive-url=https://web.archive.org/web/20170917212442/http://bmw3series.johnavis.com/blog/654/m50-engine-e36|archive-date=2017-09-17|url-status=dead}}

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| File: BMW M20 Engine.JPG

| M20 engine- exhaust side

| File: BMW M20 engine in BMW-Museum in Munich, Bayern.JPG

| M20 engine- intake side

| File:M20B25 block.jpg

|M20 engine- block

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File:BMW e21 engine.JPG

The first models to use the M20 were the E12 520/6 and the E21 320/6, which used a {{convert|1991|cc|cuin|0|abbr=on}} version known as the M20B20VE or M60/2.{{cite web|url=https://www.carfolio.com/specifications/models/car/?car=119361|title=1977 BMW 520|publisher=}}{{cite web |url=https://www.specs4bmw.com/e21/3-series/sedan |title=BMW E21 3-series Sedan specs | Specs4BMW.com |accessdate=2015-12-21 |url-status=dead |archiveurl=https://web.archive.org/web/20150627125125/http://www.specs4bmw.com/e21/3-series/sedan |archivedate=2015-06-27 }} This engine uses a bore of {{Convert|80|mm|in|2|abbr=on}} and a stroke of {{Convert|66|mm|in|2|abbr=on}}. A Solex 4A1 four-barrel carburetor was used in the M20B20VE ("VE" is for vergaser- "carburettor" in German),{{Cite book | title = World Cars 1981 | publisher = The Automobile Club of Italy/Herald Books | editor-last = Lösch | editor-first = Annamaria | location = Pelham, NY | page = 107 | year = 1981 | isbn = 0-910714-13-4 }} 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,{{cite web|url=https://www.automobile-catalog.com/car/1982/262835/bmw_520i_4-speed.html|title=1982 BMW 520i 4-speed (for Europe) specs review|work=www.automobile-catalog.com}} with Bosch K-Jetronic used in a {{convert|92|kW|0|abbr=on}} version called the M20B20KE.{{cite journal |title=Automobil Revue |date=1983 |page=205}} 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|date=February 2019}} The "M60" designation was dropped and this version was known as the M20B20LE.{{cite book | title = Automobil Revue 1987 | editor-last = Büschi | editor-first = Hans-Ulrich | publisher = Hallwag AG | location = Berne, Switzerland | language = German, French | pages = 184–186 | volume = 82 |date=March 5, 1987 | isbn = 3-444-00458-3 }}

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.{{cite web|url=https://www.e30club.com/bmw-e30|archive-url=https://web.archive.org/web/20111126124748/http://www.e30club.com/bmw-e30|url-status=usurped|archive-date=2011-11-26|title=BMW e30 - BMW e30 Club}}

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

Applications:

• 1977–1981 E12 5 Series 520/6 (carburettor)
• 1977–1982 E21 3 Series 320/6 (carburettor)
• 1981–1982 E28 5 Series 520i (K-Jetronic){{cite web|title=5' E28 520i FUEL INJECTION K-JETRONIC|url=https://www.realoem.com/bmw/en/showparts?id=4071-EUR-07-1981-E28-BMW-520i&diagId=13_0150|website=www.realoem.com|accessdate=21 September 2017}}
• 1982–1984 E28 5 Series 520i (L-Jetronic){{cite web|title=5' E28 520i Control unit L-jetronic|url=https://www.realoem.com/bmw/en/showparts?id=4051-EUR-01-1983-E28-BMW-520i&diagId=13_0241|website=www.realoem.com|accessdate=21 September 2017}}
• 1982–1984 E30 3 Series 320i (L-Jetronic)
• 1984–1987 E28 5 Series 520i (LE-Jetronic){{cite web|title=5' E28 520i Control unit L-jetronic|url=http://www.realoem.com/bmw/en/showparts?id=4051-EUR-08-1985-E28-BMW-520i&diagId=13_0241|website=www.realoem.com|accessdate=21 September 2017}}
• 1984–1987 E30 3 Series 320i (LE-Jetronic)
• 1986–1987 E28 5 Series 520i (Motronic){{cite web|title=5' E28 520i Uncoded DME control unit|url=https://www.realoem.com/bmw/en/showparts?id=4031-EUR-07-1987-E28-BMW-520i&diagId=12_1305|website=www.realoem.com|accessdate=21 September 2017}}
• 1987–1992 E30 3 Series 320i (Motronic)
• 1988–1990 E34 5 Series 520i (Motronic)
• 1989–1992 Bertone Freeclimber (Freeclimber I)

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 {{Convert|76.8|mm|in|2|abbr=on}} stroke crank. The bore is {{Convert|80|mm|in|2|abbr=on}} and it has a capacity of {{convert|2316|cc|L|1|abbr=on}}. Fuel injection was K-Jetronic, the compression ratio is 9.5:1, the power output is {{convert|105|kW|PS hp|0|abbr=on}} and the redline is 6,400 rpm.

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 {{convert|102|kW|0|abbr=on}}.

In September 1983, the M20B23LE's fuel-injection, exhaust and camshaft were upgraded and power increased to {{convert|110|kW|0|abbr=on}} with a redline of 6,500 rpm. The {{convert|102|kW|0|abbr=on}} version continued to be available in certain markets with strict emissions regulations (such as Switzerland) until replaced by the 325i.{{cite book | title = Automobil Revue '84 | editor-last = Büschi | editor-first = Hans-Ulrich | publisher = Hallwag, AG | language = German, French | page = 179 | location = Berne, Switzerland | volume = 79 | date = March 1, 1984 | isbn = 3-444-06070-X }}

The M20B23 versions were not sold in North America.

Applications:

• 1977–1982 E21 3 Series 323i (K-Jetronic){{cite web|url=https://www.bmwheaven.com/database/show.php?id=133|title=BMW Heaven Specification Database - Specifications for BMW 323i E21 (1977-1982)|author=Ilir Dibrani|publisher=www.bmwheaven.com}}
• 1982–1984 E30 3 Series 323i (L-Jetronic)
• 1984–1987 E30 3 Series 323i (LE-Jetronic)

In 1985, the M20B25 replaced the M20B23. The M20B25 has a capacity of {{convert|2494|cc|cuin|1|abbr=on}} and initially produced {{cvt|171|PS|kW PS hp|0|order=out}} (without a catalytic converter).{{cite web|url=https://www.bmwheaven.com/database/engine.php?type=M20|title=BMW Heaven Specification Database - Engine specifications for M20 engines|first=Ilir | last = Dibrani|publisher=www.bmwheaven.com}} It has an upgraded cylinder head (known as "885"), a bore of {{convert|84|mm|in|2|abbr=on}}, a stroke of {{convert|75|mm|in|2|abbr=on}}, a compression ratio of 9.4:1, a redline of 6,500 rpm and uses Bosch Motronic 1.1 engine management.{{cite web|url=https://e30world.com/specifications/BMW-E30-specs-table |title= BMW E30 Specifications |website=www.e30world.com |url-status=dead |archiveurl=https://web.archive.org/web/20130224032538/http://e30world.com/specifications/BMW-E30-specs-table |archivedate=24 February 2013}}

In 1987, a catalyzed model with Motronic 1.3 engine management was introduced.{{cite web|title=3' E30 325i Uncoded DME control unit|url=https://www.realoem.com/bmw/en/showparts?id=1411-EUR-01-1988-E30-BMW-325i&diagId=12_0856|website=www.realoem.com|accessdate=21 September 2017}} The compression ratio was reduced to 8.8:1 but thanks to the more sophisticated electronics power remained nearly as before, at {{cvt|170|PS|kW PS hp|0|order=out}}. The uncatalyzed engine was kept in production for Southern Europe and other markets where unleaded petrol was not regularly available.

Applications:

• 1985–1993 E30 3 Series 325i
• 1989–1990 E34 5 Series 525i
• 1988–1991 Z1

The M20B27 was designed for efficiency (thus the e for the Greek letter eta in 325e) and low-rev torque.{{cite web|url=https://www.e30info.com/pages/diff.htm|title=BMW e30 1983-1991 differences between models|publisher=www.e30info.com}} 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 {{convert|75|to|81|mm|in|2|abbr=on}}, resulting in a capacity of {{convert|2693|cc|cuin|1|abbr=on}}. 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 {{Convert|84|mm|in|2|abbr=on}}. 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 {{convert|123|hp|kW|0|abbr=on|order=flip}} and {{convert|177|lb·ft|N.m|abbr=on|order=flip}} at 3,250 rpm for models without a catalytic converter. Models with a catalytic converter produce {{convert|121|hp|kW|0|abbr=on|order=flip}} and {{convert|170|lb·ft|N.m|abbr=on|order=flip}}.

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.{{cite magazine | ref = AG94 | magazine = De AutoGids | number = 94 | volume = 4 | page = 130 | title = BMW: Met de ETA op de zuinige tor | trans-title = BMW: With Eta on an economy run | first = Vic | last = Heylen | language = Dutch | date = 1983-04-28 | publisher = Uitgeverij Auto-Magazine | location = Brussels, Belgium }} 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 {{convert|95|kW|0|abbr=on}} despite a lower compression ratio of 10.3:1.{{cite web|title=M20B27 Engine Specs|url=https://www.e30tech.com/forum/showthread.php?t=13930|website=www.e30tech.com|accessdate=21 September 2017|archive-url=https://web.archive.org/web/20170923095550/http://www.e30tech.com/forum/showthread.php?t=13930|archive-date=23 September 2017|url-status=dead}}

In late 1987, the fuel injection was upgraded to Motronic 1.3 on the US market plastic bumper 325e and 528e 'Super Eta',Automobil Revue '83, p. 206{{cite book | title = Auto Katalog 1986 | publisher = Vereinigte Motor-Verlage GmbH & Co. KG | editor-last = Heitz | editor-first = Rudolf | location = Stuttgart | page = 210 | volume = 29 | language = German | date = 1985-08-01 | id = 81530/85001 }} 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.{{cite web|title=325e|url=https://www.e30zone.net/e30zonewiki/index.php/325e|website=www.e30zone.net|accessdate=21 September 2017}} Power output increased to {{convert|127|hp|kW|0|abbr=on|order=flip}} 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 {{convert|145|kW|hp|0|abbr=on}} and the second revision, often referred to as "Evo2" or on the VIN plate as "HP2" produced {{convert|155|kW|hp|0|abbr=on}}.

Applications:

• 1982–1987 E30 3 Series 325e, 325e
• 1982–1988 E28 5 Series 525e (called 528e in North America)
• 1989–1992 E30 3 Series 325iS (only available in South Africa)
• 1989–1992 Bertone Freeclimber (Freeclimber I)

{{Commons category|BMW M20 engine}}

• BMW
• List of BMW engines

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{{BMW automotive petrol engines: 1960s to 1980s}}

{{DEFAULTSORT:Bmw M20}}

M20

Category:Straight-six engines

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