BMW M20
Template:Infobox automobile engine
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.<ref>Template:Cite web</ref>
The first cars to use the M20 were the E12 5 Series and the E21 3 Series. The initial M20 model had a displacement of Template:Convert, with later versions having displacements of up to Template:Convert.<ref>Template:Cite web</ref>
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 wagon (estate) and convertible model built in April 1993.<ref>Template:Cite web</ref>
The M20 was the basis for the BMW M21 diesel engine.<ref>Template:Cite web</ref> It is also loosely related to the BMW M70 V12 petrol engine.
History
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.<ref>Template:Cite book</ref>Template:Refpage The resulting M20 had a displacement of Template:Convert, 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.<ref>BMW AG (ed.): IAA Frankfurt/Main 15.9. bis 25.9.1977, p. 5, retrieved 17 September 2021</ref> Later versions had displacements up to Template:Convert. 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",<ref>Template:Cite web</ref><ref>Template:Cite web</ref> although the M60 designation has since been re-used for a V8 engine produced from 1992 to 1996.
Design
As per the M30, the M20 has an iron block, aluminium head and a SOHC valvetrain with 2 valves per cylinder.<ref>Template:Cite web</ref> It has a traditional rocker arm design and no hydraulic tappets.<ref>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</ref> The major differences to the M30 are:
- A timing belt rather than a timing chain<ref>Template:Cite web</ref>
- Bore spacing of Template:Convert, rather than Template:Convert<ref>Template:Cite web</ref>
- Slant angle of 20 degrees, compared with 30 degrees for the M30.<ref>Template:Cite web</ref>
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Models
| Version | Displacement | Power | Torque | Years | Notes |
|---|---|---|---|---|---|
| M20B20 | Template:Convert | Template:Cvt at 6,000 rpm<ref name="1977 IAA">Template:Cite web</ref> |
Template:Convert at 4,000 rpm |
1977-1982 | Austrian models rated at Template:Cvt<ref>Template:Cite web</ref> |
| Template:Cvt at 5,800 rpm |
Template:Convert at 4,000 rpm |
1982-1984 | |||
| Template:Convert at 4,000 rpm |
1984-1987 | ||||
| Template:Cvt at 6,000 rpm |
Template:Convert at 4,300 rpm |
1986-1992 | |||
| M20B23 | Template:Convert | Template:Cvt at 5,300 rpm<ref name="1977 IAA"/> |
Template:Convert at 4,500 rpm |
1977-1982 | |
| Template:Cvt at 5,300 rpm |
Template:Convert at 4,000 rpm |
1982-1983 | |||
| Template:Cvt at 6,000 rpm |
1983-1987 | ||||
| M20B25 | Template:Convert | Template:Cvt at 5,800 rpm |
Template:Convert at 4,000 rpm |
1985-1990 | |
| Template:Cvt at 5,800 rpm |
Template:Convert at 4,300 rpm |
1987-1992 | Catalyzed | ||
| M20B27 | Template:Convert | Template:Cvt at 4,250 rpm |
Template:Convert at 3,250 rpm |
1982-1985 | US models rated at Template:Cvt |
| Template:Cvt at 4,250 rpm |
Template:Convert at 3,250 rpm |
1985-1987 | Austrian models rated at Template:Cvt<ref>Template:Cite web</ref><ref>Template:Cite web</ref> | ||
| Template:Cvt at 4,250 rpm |
Template:Convert at 3,250 rpm |
1985-1988 |
M20B20
The first models to use the M20 were the E12 520/6 and the E21 320/6, which used a Template:Convert version known as the M20B20VE or M60/2.<ref name="carfolio_520">Template:Cite web</ref><ref>Template:Cite web</ref> This engine uses a bore of Template:Convert and a stroke of Template:Convert.<ref name="carfolio_520" /> A Solex 4A1 four-barrel carburetor was used in the M20B20VE ("VE" is for vergaser- "carburettor" in German),<ref name="WC81">Template:Cite book</ref> 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,<ref>Template:Cite webTemplate:Dead link</ref> with Bosch K-Jetronic used in a Template:Convert version called the M20B20KE.<ref>Template:Cite journal</ref> 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.Template:Citation needed The "M60" designation was dropped and this version was known as the M20B20LE.<ref name="AR87">Template:Cite book</ref>
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.<ref name="e30club">Template:Cite web</ref><ref name="AR87"/>
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)<ref>Template:Cite web</ref>
- 1982–1984 E28 5 Series 520i (L-Jetronic)<ref>Template:Cite web</ref>
- 1982–1984 E30 3 Series 320i (L-Jetronic)
- 1984–1987 E28 5 Series 520i (LE-Jetronic)<ref>Template:Cite web</ref>
- 1984–1987 E30 3 Series 320i (LE-Jetronic)
- 1986–1987 E28 5 Series 520i (Motronic)<ref>Template:Cite web</ref>
- 1987–1992 E30 3 Series 320i (Motronic)
- 1988–1990 E34 5 Series 520i (Motronic)
- 1989–1992 Bertone Freeclimber (Freeclimber I)
M20B23
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 Template:Convert stroke crank. The bore is Template:Convert and it has a capacity of Template:Convert. Fuel injection was K-Jetronic, the compression ratio is 9.5:1, the power output is Template:Convert<ref name="1977 IAA"/> and the redline is 6,400 rpm.<ref name="WC81"/>
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 Template:Convert.
In September 1983, the M20B23LE's fuel-injection, exhaust and camshaft were upgraded and power increased to Template:Convert with a redline of 6,500 rpm. The Template:Convert version continued to be available in certain markets with strict emissions regulations (such as Switzerland) until replaced by the 325i.<ref name="AR84">Template:Cite book</ref>
The M20B23 versions were not sold in North America.
Applications:
- 1977–1982 E21 3 Series 323i (K-Jetronic)<ref name="bmwheaven_323i">Template:Cite web</ref>
- 1982–1984 E30 3 Series 323i (L-Jetronic)
- 1984–1987 E30 3 Series 323i (LE-Jetronic)
M20B25
In 1985, the M20B25 replaced the M20B23. The M20B25 has a capacity of Template:Convert and initially produced Template:Cvt (without a catalytic converter).<ref name="bmwheaven_M20">Template:Cite web</ref> It has an upgraded cylinder head (known as "885"), a bore of Template:Convert, a stroke of Template:Convert, a compression ratio of 9.4:1, a redline of 6,500 rpm and uses Bosch Motronic 1.1 engine management.<ref name="e30world">Template:Cite web</ref><ref name="AR87"/>
In 1987, a catalyzed model with Motronic 1.3 engine management was introduced.<ref>Template:Cite web</ref><ref name="AR87"/> The compression ratio was reduced to 8.8:1 but thanks to the more sophisticated electronics power remained nearly as before, at Template:Cvt. 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
M20B27
The M20B27 was designed for efficiency (thus the e for the Greek letter eta in 325e) and low-rev torque.<ref>Template:Cite web</ref> 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 Template:Convert, resulting in a capacity of Template:Convert.<ref name="e30world" /> 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 Template:Convert. 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 Template:Convert and Template:Convert at 3,250 rpm for models without a catalytic converter.<ref name="e30world" /> Models with a catalytic converter produce Template:Convert and Template:Convert.
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.<ref name=AG941>Template:Cite magazine</ref> 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 Template:Convert despite a lower compression ratio of 10.3:1.<ref>Template:Cite web</ref>
In late 1987, the fuel injection was upgraded to Motronic 1.3 on the US market plastic bumper 325e and 528e 'Super Eta',<ref>Automobil Revue '83, p. 206</ref><ref name="AK86">Template:Cite book</ref> 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.<ref>Template:Cite web</ref> Power output increased to Template:Convert 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 Template:Convert and the second revision, often referred to as "Evo2" or on the VIN plate as "HP2" produced Template:Convert.
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)