BMW M20
From Wikipedia, the free encyclopedia
| BMW M20 engine | |
|---|---|
| Manufacturer | BMW |
| Production | 1965–1994 |
| Predecessor | None |
| Successor | BMW M50 |
| Class | Straight-6 |
| Engine | 2.0 L (1990 cc/121 in³) 2.3 L (2316 cc/141 in³) 2.5 L (2494 cc/152 in³) 2.7 L (2693 cc/164 in³) |
| Similar | Mercedes-Benz M110 |
The M20 was an I6 piston engine of BMW.
The 12-valve, belt driven SOHC design was introduced in the 1976 BMW 520/6 and 320/6. With displacements ranging from 2.0 to 2.7 liters, it was the "little brother" to the larger BMW M30 engine.
Powering the E21 and E30 3-Series, as well as E12, E28 and E34 5-Series cars, it was produced for four decades, with the last models of the E30 325i touring built in 1992. At that time, the newer M50 engines with 4 valves and DOHC were already used in the E36 and E34 for some years.
As the BMW M21, it became a diesel engine that was also available with a turbocharger.
Contents |
[edit] M20B20
The small 2.0 liter engine, used as the entry-level version to the six cylinder ranges, ran smoothly but lacked torque and required higher revs, resulting in higher fuel consumption. It was never exported to North America due to federal emissions regulations. It used the same cylinder head casting as the 2.3 L M20 in the E12 and E21 2.3 L motors and the pre-1987 2.7 L eta motors. All of the 2.0 L versions were carbureted until the E30 320i, which used Bosch Motronic version 1.1/1.3 to work with a catalytic converter.
Applications:
[edit] M20B23
The 323i began as an E21 model and continued with better fuel injection and several internal revisions in the E30 323i. The E21 used the same cylinder head casting as the standard 2.7 L eta cars, only drilled from the factory to oil a seven-bearing cam. The E30 323 head is similar to the E21 323 head but with larger intake ports. It shares its combustion chamber design, water jacket and valves with the 2.7 L eta and early 2.0 and 2.3 L castings.
Applications:
[edit] M20B25
The German version of the M20B25 produced 170 hp with a catalytic converter and 171 without. It featured a 12-valve SOHC head with larger valves, 84 mm (3.3 in) bore, and 75 mm (3 in) stroke. Most significantly it had redesigned pistons and combustion chambers for better power, more resistance to detonation and higher thermodynamic efficiency. It was equipped with Bosch Motronic 1.1/1.3 Adaptive fuel injection. With a minor modification that adjusts the idle speed of a cold engine, the 325i fulfills Euro 2 emission requirements in Germany, resulting in a lower tax compared to Euro 1 (as of 2005).
Applications:
[edit] M20B27
The 2.7 L M20B27 was designed for efficiency (thus the e for the Greek letter eta in 325e). It had an 84 mm (3.3 in) bore and with 81 mm (3.2 in) a longer stroke, for a total displacement of 2693 cc. The eta only utilizes four camshaft bearings for reduced internal friction, though the heads still have seven journals cast into the head. These heads can be drilled to oil a seven bearing cam.
Output was 121 hp at 4250 RPM for all models produced through model year 1987 and 127 hp at 4800 RPM for the final year of production in 1988. Peak torque is 170 ft·lbf at about 3250 RPM for all years of the eta. This was the first engine BMW built with fuel economy as the top priority. In production it was coupled to either a 2.93:1 differential for the E28 5 series and most E30 3 series models or a 2.79:1 for early E30 3 series cars with manual transmissions. The tall final drive gearing was required to keep the engine in its best operating range at various road speeds. These features did achieve exceptional efficiency, but at the expense of the performance typically associated with the marque.
It is interesting to note that despite slightly less torque and roughly ten percent less displacement, the 2.5l E30 325i accelerates much quicker. Released for model year 1987 in the US market, it was intended to replace the E21 323i as the high performance, non-M model in the 3 series line. In addition to the more conventional engine tuning, it was built with a 3.73:1 final drive ratio in the US market. This equates to lower torque at the wheels on eta cars and results in substantially milder acceleration.
All eta engines used Bosch Motronic engine management systems that were calibrated for maximum fuel economy. The result was a very conservative spark advance curve and fuel delivery curve. In addition, the Motronic had a built-in rev limiter that engaged at about 4750 rpm. This very low redline was the result of the four bearing cam, soft valve springs, intake manifold and camshaft design. Due to the very low overlap and short duration of the cam and the intake manifold tuning, the motor does not make any power over about 5,000 RPM.
For the 1988 model year, the eta cars got a refresh from the factory. This included a newer Bosch Motronic version with adaptive idle control, a 325i head casting with the larger valves, ports, revised combustion chambers and water jacket, new pistons to fit the 2.7 L stroke with the 2.5 L head, a dual exhaust system and a 5300 RPM rev limit. Though it only made slightly more power in stock form, it could be easily boosted by bolting on a 325i head, a complete 325i intake manifold and throttle and plugging in the 325i engine control unit. Depending on which cam, chip and intake is used, the combination can make over 180 horsepower with the stock compression ratio.
In aftermarket modifications that are inspired by custom versions of Alpina and AC Schnitzer, the long-stroke eta engine block is often combined with a 325i head to a so-called 327i that combines the high low-rev torque of the eta with the top-range power of the 325i.
Applications:
- 325/325e/325es
- 1982–1987 525e (or 528e in the US)
[edit] Overview
| Engine | Displacement | Power | Torque | Redline | Year |
|---|---|---|---|---|---|
| M20B20 | 2.0 L (1990 cc/121 in³) | 92 kW (123 hp) @ 5800 | 165 N·m (121 ft·lbf) @ 4000 | 1981 | |
| 92 kW (123 hp) @ 5800 | 170 N·m (125 ft·lbf) @ 4000 | 1981 | |||
| 95 kW (127 hp) @ 6000 | 174 N·m (128 ft·lbf) @ 4000 | 6200 | 1985 | ||
| 95 kW (127 hp) @ 6000 | 164 N·m (120 ft·lbf) @ 4300 | 6200 | 1986 | ||
| M20B23 | 2.3 L (2316 cc/141 in³) | 102 kW (136 hp) @ 5300 | 205 N·m (151 ft·lbf) @ 4000 | 1982 | |
| 110 kW (147 hp) @ 6000 | 205 N·m (151 ft·lbf) @ 4000 | 1983 | |||
| M20B25 | 2.5 L (2494 cc/152 in³) | 126 kW (168 hp) @ 5800 | 226 N·m (166 ft·lbf) @ 4000 | 6200 | 1985 |
| 120 kW (160 hp) @ 5800 | 215 N·m (158 ft·lbf) @ 4000 | 6200 | 1985 | ||
| 125 kW (167 hp) @ 5800 | 222 N·m (163 ft·lbf) @ 4300 | 6200 | 1987 | ||
| M20B27 | 2.7 L (2693 cc/164 in³) | 92 kW (123 hp) @ 4250 | 240 N·m (177 ft·lbf) @ 3250 | 1983 | |
| 95 kW (127 hp) @ 4250 | 240 N·m (177 ft·lbf) @ 3250 | 1986 | |||
| 90 kW (120 hp) @ 4250 | 230 N·m (169 ft·lbf) @ 3250 | 1985 | |||
| 95 kW (127 hp) @ 4800 | 230 N·m (169 ft·lbf) @ 3200 | 1986 |
