All power units of the M20 series are in-line injector motors complete with a single camshaft. BMW E12/E21 cars began to be equipped with these motors in 1977. The last unit was released in 1993. The minimum displacement of all units is not less than two liters. The latest engine is the M20B27, which has this figure closer to three (2.7 liters).
Then German engineers used this engine to produce the M21 series of diesel units.
M20B27 engine specifications
| Power, hp. | 122 – 129 |
| Fuel type | Gasoline |
| Volume, cm*3 | 2693 |
| Maximum torque, N*m (kg*m) at rpm. | 230 (23) / 3200; 230 (23) / 3250; 240 (24) / 3250 |
| Engine type | In-line, 6-cylinder, injector. |
| Cylinder diameter, mm | 84 |
| Number of valves per cylinder | 2 |
| Maximum power, hp (kW) at rpm. | 122 (90) / 4250; 125 (92) / 4250; 129 (95) / 4250; 129 (95) / 4800 |
| Blower | No |
| Compression ratio | 8.8 – 11 |
| Piston stroke, mm | 81 |
Advantages
The largest power unit is more tractive at low rpm. The B27 is interchangeable with the B25, but it has a larger piston stroke with a larger cylinder bore. The cylinder head is also slightly different from the B25 modification. German engineers used a different camshaft. However, the valves remained in place.
The engine functions more efficiently due to the soft valve springs, which are able to absorb more energy. A different intake manifold is used here. It has longer ducts. The throttle is the same. It is the same on all M20 engines. These changes have reduced the maximum revolutions of the power unit to 4800 rpm. The North American/European market was supplied cars with units with 11:1/9:1 compression.
From 1982 to 1987/88. The M20B27 turbo was fitted to the BMW E30/E28.
Disadvantages
- Overheating. In case of defective cooling system of the vehicle, the cylinder head heats up quickly. Check the pump, radiator, thermostat, air plugs in the system;
- Wear of camshaft pastels. Such a problem appears when the engine has a mileage of 200-250 thousand. A sign of wear is the knocking of the camshaft. It is necessary to purchase a new cylinder head;
- Crack in the cylinder-head. The cause is engine overheating. It is impossible to eliminate the crack. It is necessary to buy another cylinder head;
- M20B27 has a high rpm when driving. The problem is the idle valve. It should be open when cold, and as the engine warms up it should close;
- M20B27 has 1100 rpm at idle. Most likely the breather on the back side of the valve cover is dirty. It should be thoroughly flushed out. Also, the throttle plate should close completely. It may also be contaminated.
Chip tuning
If you decide to perform tuning of the M20V27 stroker engine, you need to think about whether it is worth it. After all, this is an old powertrain. Maybe it is better to replace the motor? If you decide to do this operation, say that by removing the catalytic converter and installing a turbine, you can bring the power to 200 “horses”.
A good option for owners of older BMWs is to have the system re-flashed. This will allow you to get a more modern system and better dynamics. Many motorists want to get better traction “at the lows”, and some citizens install systems oriented to specific operating conditions.
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