BMW M20B25

BMW M20B25The 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 modelM20B25
Engine typeStraight-six, 4-stroke, SOHC
Displacement2.5 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 systemLiquid-cooled
Fuel systemElectronic fuel injection
Starting systemElectric starter 12V
Firing order:1-5-3-6-2-4
Dimensions (L x W X H)
Dry weight170 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)


ModelYears Produced
BMW 325i (E30)1985–1993
BMW 525i (E34)1989–1990
BMW Z11988–1991


1. BMW TIS (Technical Information System)

Author: Sergei Wers
About: Co-founder and CEO of a multi-brand auto repair shop (engine repair, chassis repair, body repair and painting) for over 15 years. I have been developing internet sites with technical specifications for more than seven years.

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We try to use official documentation and verify the published data, but errors may occur. In addition, specifications of machinery and equipment may vary depending on markets and modifications. We do not recommend the use of this data for spare parts or repairs. Use official service manuals or parts catalogs for your product.

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