The BMW M20B25 is a 2.5 L (2,494 cc, 152.2 cu·in) straight-six, natural aspirated four-stroke gasoline engine, manufactured by BMW from 1985 to 1991.
Cylinder bore and piston stroke are 84.0 mm (3.31 in) and 75.0 mm (2.95 in), respectively. The compression ratio rating is 9.7:1, 9.3:1, 8.8:1 depending on the year.
This engine produced from 170 PS (125 kW; 168 HP) at 5,800 rpm to 171 PS (126 kW; 169 HP) at 5,800 rpm of horsepower and from 215 N·m (21.9 kg·m, 158.5 ft·lb) at 4,000 rpm to 222 N·m (22.6 kg·m, 163.6 ft·lb) at 4,300 rpm of peak torque.
The BMW M20B25 features:
- Cast-iron block and Aluminum head
- SOHC (single overhead camshaft) design
- Electronic fuel injection
- Bosch Motronic 1.1 DME (1986-1986), Bosch Motronic 1.1 DME (after 1987)
- Pressurazed lubrication system
- Liquid-cooled cooling system
General information
| Engine Specifications | |
| Engine model | M20B25 |
| Engine type | Straight-six, 4-stroke, SOHC |
| Displacement | 2.5 L, 2,494 cm3, (152.2 cu·in) |
| Max. horsepower |
From 170 PS (125 kW; 168 HP) at 5,800 rpm to 171 PS (126 kW; 169 HP) at 5,800 rpm |
| Max. torque |
From 215 N·m (21.9 kg·m, 158.5 ft·lb) at 4,000 rpm to 222 N·m (22.6 kg·m, 163.6 ft·lb) at 4,300 rpm |
| Cooling system | Liquid-cooled |
| Fuel system | Electronic fuel injection |
| Starting system | Electric starter 12V |
| Firing order: | 1-5-3-6-2-4 |
| Dimensions (L x W X H) | – |
| Dry weight | 170 kg (374.8 lbs) |
Cylinder Block and Head
| Cylinder block | |
| Cylinder block alloy: | Cast-iron |
| Compression ratio: |
Before 1987: 9.7:1, After 1987: 9.3:1, with catalytic converters: 8.8:1 |
| Cylinder bore: | 84.0 mm (3.31 in) |
| Piston stroke: | 75.0 mm (2.95 in) |
| Cylinder internal diameter (standard): | 84.000 mm (3.3071 in) |
| Piston skirt outer diameter (standard): | 83.980 mm (3.3063 in) |
| Number of piston rings (compression / oil): | 2/1 |
| Number of main bearings: | 7 |
| Crankshaft center distance: | 37.5 mm (1.475 in) |
| Cylinder head | |
| Cylinder head alloy: | Aluminium |
| Valve arrangement: | SOHC, belt driven |
| Valves: | 2,(12 valves in total) |
| Valve head diameter (INTAKE): | 42.0 mm (1.6535 in) |
| Valve head diameter (EXHAUST): | 36.0 mm (1.4173 in) |
| Valve lift (INTAKE): | 10.100 mm (0.3976 in) |
| Valve lift (EXHAUST): | 10.100 mm (0.3976 in) |
Service Data
| Engine speed | |
| Redline: | 750-800 rpm |
| Idle speed: | 750-800 rpm |
| Compression pressure | |
| Minimum: | 10.2 kg/cm2 (9.9 bar, 145 psi) / 350 rpm |
| Valve clearance | |
| Intake valve clearance (COLD): | 0.25 mm (0.0098 in) |
| Exhaust valve clearance (COLD): | 0.25 mm (0.0098 in) |
| Oil system | |
| Recommended oil: | SAE 5W-30, 10W-30 |
| Oil capacity: |
With filter change: 4.25 L (4.5 US. qt, 3.7 Imp. qt.) Without filter change: 4.0 L (4.2 US. qt, 3.5 Imp. qt.) |
| Oil change interval km,(miles): | 10,000 (6,000) |
| Ignition system | |
| Spark plug: | Bosch: W8LCR, NGK: ZGR5A |
| Spark plug gap: | 0.7 mm (0.0276 in) |
Applications
| Model | Years Produced |
| BMW 325i (E30) | 1985–1993 |
| BMW 525i (E34) | 1989–1990 |
| BMW Z1 | 1988–1991 |