BMW N52B25

BMW N52B25The BMW N52B25 is a 2.5 liters (2,497 cc, 152.4 cu·in) straight-six, liquid-cooled, four-stroke cycle natural aspirated gasoline engine from BMW N52-family. The engine was manufactured on Munich Plant (Munich, Germany) from 2005 to 2011.

The BMW N52B25 engine features a magnesium-aluminum alloy cylinder block. The aluminum cylinder head uses chain-driven double overhead camshafts (DOHC) and four valves per cylinder (24 valves in total). It is equipped with a Siemens MSV70 engine management system, double VANOS (Variable Valve Timing System from BMW), Valvetronic (Variable Valve Lift system), electronic controlled throttle, variable-length intake manifold (called “DISA” by BMW), a distributorless ignition system with individual ignition coils for each cylinder.

Cylinder bore and piston stroke are 82.0 mm (3.23 in) and 79.0 mm (3.11 in), respectively. The compression ratio rating is 11.0:1.

The N52B25 engine had three modifications:

  1. N52B25O1 this modification was manufactured from 2005 to 2008, and used for BMW models with 25i index. This engine produced 218 PS (160 kW; 215 HP) at 6,500 rpm of horsepower and 250 N·m (25.5 kg·m, 184.3 ft·lb) at 2,750-3,000 rpm of torque.
  2. N52B25U1 this version with decreased level of HP was manufactured from 2005 to 2010 and used for BMW models with 23i index. This version produced 177 PS (130 kW; 174 HP) at 6,500 rpm of output power and 230 N·m (23.5 kg·m, 169.5 ft·lb) at 3,500-5,000 rpm of torque.
  3. N52B25 this version was equipped with another intake manifoldand was was manufactured from 2009 to 2011. This version produced 204 PS (150 kW; 201 HP) at 6,400 rpm of output power and 250 N·m (25.5 kg·m, 184.3 ft·lb) at 2,750-4,250 rpm of torque, and used for BMW models with 23i index.

The breakdown of the engine code is as follows:

  • N – New engine generation
  • 5 – Six-cylinder
  • 2 – Valvetronic
  • B – Gasoline
  • 25 – 2.5 Liter Displacement

General information

Engine Specifications
Engine codeN52B25
LayoutFour stroke, Inline-6 (Straight-6)
Fuel typeGasoline
Displacement2.5 L, 2,494 cc (152.2 cu in)
Fuel systemFuel injection system
Power adderNone
Max. horsepower N52B25O1: 218 PS (160 kW; 215 HP) at 6,500 rpm
N52B25U1: 177 PS (130 kW; 174 HP) at 6,500 rpm
N52B25: 204 PS (150 kW; 201 HP) at 6,400 rpm
Max. torque N52B25O1: 250 N·m (25.5 kg·m, 184.3 ft·lb) at 2,750-3,000 rpm
N52B25U1: 230 N·m (23.5 kg·m, 169.5 ft·lb) at 3,500-5,000 rpm
N52B25: 250 N·m (25.5 kg·m, 184.3 ft·lb) at 2,750-4,250 rpm
Firing order1-5-3-6-2-4
Dimensions (L x H x W):
Weight161 kg (353 lbs)

Cylinder block

The N52B25 engine used a magnesium-aluminum alloy cylinder block, Alusil cylinder bores, cast iron crankshaft with seven main bearing journals, trapezoidal connecting rods (i.e. tapered small ends), aluminum pistons, and a lightweight thermoplastic intake manifold.

The cylinder bore is 82.0 mm (3.23 in) and the piston stroke is 79.0 mm (3.11 in). The compression ratio rating is 11.0:1.

Cylinder block
Cylinder block alloyMagnesium-aluminum alloy
Compression ratio:11.0:1
Cylinder bore:82.0 mm (3.23 in)
Piston stroke:79.0 mm (3.11 in)
Number of piston rings (compression / oil):2 / 1
Number of main bearings:7
Cylinder inner diameter (standard):82.000-82.014 mm (3.2283-3.2289 in)
Piston skirt diameter (standard):81.985 mm (3.2277 in)
Piston pin outer diameter:
Piston ring side clearance:Top0.020-0.060 mm (0.0008-0.0024 in)
Second0.020-0.060 mm (0.0008-0.0024 in)
Piston ring end gap:Top0.180-0.330 mm (0.0071-0.013 in)
Second0.300-0.500 mm (0.0118-0.0197 in)
Crankshaft journal diameter:56.000 mm (2.2047 in)
Crankpin diameter:50.000 mm (1.9685 in)

Cylinder head

The cylinder head is made of Aluminium silicon (Alusil). The N52B25 engine uses chain-driven double overhead camshafts and four valves per cylinder. The N52B25 engine is equipped with BMW’s double VANOS on intake and exhaust camshafts and Valvetronic II system.

Standart head height is 112.0 mm (4.40 in). Intake valves are 32.2 mm (1.27 in) in diameter and exhaust valves are 27.0 mm (1.063 in). Valve clearance is set by self-adjusting (zero-lash) hydraulic lifters for reduced valve noise and the elimination of routine valve adjustment.

Cylinder head
Cylinder head alloyAluminum
Valve Arrangement:DOHC, chain driven
Valves:24 (4 valves per cylinder)
Head height:112.0 mm (4.4094 in)
Valve head diameter:INTAKE32.2 mm (1.2677 in)
EXHAUST27.0 mm (1.063 in)
Valve steam diameter:INTAKE5.000 mm (0.1969 in)
EXHAUST6.000 mm (0.2362 in)

Maintenance data

Compression pressure
Minimum10.0 kg/cm2 (9.9 bar, 145 psi) / 350 rpm
Compression differential limit between cylinders:1.0 kg/cm2 (1.0 bar, 15 psi) / 350 rpm
Oil system
Recommended engine oil0W-30, 0W-40, 5W-40
Oil typeBMW LL-01
Engine oil capacity (Refill capacity)6.5 L (6.87 US. qt, 5.72 Imp. qt.)
Oil change interval, km (miles)5,000-10,000 (3,000-6,000)
Ignition system
Spark plugNGK 5987 PLZFR6A-11S or Bosch FR7NPP332
Spark plug gap:1.0 mm (0.0394 in)
Spark plug torque:23 N·m (2.3 kg·m, 17 ft·lb)

Vehicle applications

ModelYears Produced
N52B25U1 (130 kW)
BMW 323i (E90) – Canada2006
BMW 523i (E60/E61)2004-2007
BMW Z4 2.5i (E85)2006-2008
N52B25 (150 kW)
BMW 323i (E90) Canada2007-2011
BMW 523i (F10)2010-2011
BMW Z4 sDrive23i (E89)2009-2011
N52B25O1 (160 kW)
BMW X3 2.5si, xDrive25i (E83)2005-2010
BMW 525i, 525xi (E60/E61) – except U.S. and Canada2005-2010
BMW 325i, 325xi (E90/E91/E92/E93) – except U.S. and Canada2005-2011
BMW Z4 2.5si (E85)2005-2008
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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