| BMW M20 engine | |
| Production: | 1977 - 1993 |
| Configuration: | Straight-6 |
| Displacement: | 1991cc 2316cc 2494cc 2693cc |
| Bore: | 802NaN2 842NaN2 |
| Stroke: | 662NaN2 752NaN2 76.82NaN2 812NaN2 |
| Valvetrain: | SOHC |
| Fueltype: | Petrol |
| Block: | Cast iron |
| Head: | Aluminium |
| Predecessor: | None |
| Successor: | BMW 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 cars to use the M20 were the E12 5 Series and the E21 3 Series. The initial M20 model had a displacement of 20NaN0, with later versions having displacements of up to 2.70NaN0.[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 wagon (estate) 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.
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.[5] The resulting M20 had a displacement of 20NaN0, 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.[6] Later versions had displacements up to 2.70NaN0. 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.
As per the M30, the M20 has an iron block, aluminium head and a SOHC valvetrain with 2 valves per cylinder.[9] It has a traditional rocker arm design and no hydraulic tappets.[10] The major differences to the M30 are:
| Version | Displacement | Power | Torque | Years | Notes |
|---|---|---|---|---|---|
| M20B20 | 19911NaN1 | at 6,000 rpm[14] | 1630NaN0 at 4,000 rpm | 1977-1982 | Austrian models rated at [15] |
| at 5,800 rpm | 1700NaN0 at 4,000 rpm | 1982-1984 | |||
| 1740NaN0 at 4,000 rpm | 1984-1987 | ||||
| at 6,000 rpm | 1640NaN0 at 4,300 rpm | 1986-1992 | |||
| M20B23 | 23161NaN1 | at 5,300 rpm | 1900NaN0 at 4,500 rpm | 1977-1982 | |
at 5,300 rpm | 2050NaN0 at 4,000 rpm | 1982-1983 | |||
at 6,000 rpm | 1983-1987 | ||||
| M20B25 | 24941NaN1 | at 5,800 rpm | 2260NaN0 at 4,000 rpm | 1985-1990 | |
at 5,800 rpm | 2260NaN0 at 4,300 rpm | 1987-1992 | Catalyzed | ||
| 26931NaN1 | at 4,250 rpm | 2400NaN0 at 3,250 rpm | 1982-1985 | US models rated at | |
at 4,250 rpm | 2300NaN0 at 3,250 rpm | 1985-1987 | Austrian models rated at [16] [17] | ||
at 4,250 rpm | 2400NaN0 at 3,250 rpm | 1985-1988 |
The first models to use the M20 were the E12 520/6 and the E21 320/6, which used a 19910NaN0 version known as the M20B20VE or M60/2.[18] [19] This engine uses a bore of 802NaN2 and a stroke of 662NaN2. A Solex 4A1 four-barrel carburetor was used in the M20B20VE ("VE" is for vergaser- "carburettor" in German),[20] 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,[21] with Bosch K-Jetronic used in a 92kW version called the M20B20KE.[22] 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. The "M60" designation was dropped and this version was known as the M20B20LE.[23]
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.[24] [23]
The M20B20 was not sold in the United States, but was available in the E30 (320i) in Canada.
Applications:
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 76.82NaN2 stroke crank. The bore is 802NaN2 and it has a capacity of 23161NaN1. Fuel injection was K-Jetronic, the compression ratio is 9.5:1, the power output is 1050NaN0[14] and the redline is 6,400 rpm.[20]
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 102kW.
In September 1983, the M20B23LE's fuel-injection, exhaust and camshaft were upgraded and power increased to 110kW with a redline of 6,500 rpm. The 102kW version continued to be available in certain markets with strict emissions regulations (such as Switzerland) until replaced by the 325i.[29]
The M20B23 versions were not sold in North America.
Applications:
In 1985, the M20B25 replaced the M20B23. The M20B25 has a capacity of 24941NaN1 and initially produced (without a catalytic converter).[31] It has an upgraded cylinder head (known as "885"), a bore of 842NaN2, a stroke of 752NaN2, a compression ratio of 9.4:1, a redline of 6,500 rpm and uses Bosch Motronic 1.1 engine management.[32] [23]
In 1987, a catalyzed model with Motronic 1.3 engine management was introduced.[33] [23] The compression ratio was reduced to 8.8:1 but thanks to the more sophisticated electronics power remained nearly as before, at . The uncatalyzed engine was kept in production for Southern Europe and other markets where unleaded petrol was not regularly available.
Applications:
The M20B27 was designed for efficiency (thus the e for the Greek letter eta in 325e) and low-rev torque.[34] 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 75to, resulting in a capacity of 26931NaN1. 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 842NaN2. 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 123hp and 177abbr=onNaNabbr=on at 3,250 rpm for models without a catalytic converter. Models with a catalytic converter produce 121hp and 170abbr=onNaNabbr=on.
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.[35] 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 95kW despite a lower compression ratio of 10.3:1.[36]
In late 1987, the fuel injection was upgraded to Motronic 1.3 on the US market plastic bumper 325e and 528e 'Super Eta',[37] [38] 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.[39] Power output increased to 127hp 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 1450NaN0 and the second revision, often referred to as "Evo2" or on the VIN plate as "HP2" produced 1550NaN0.
Applications: