BMW N45B20 Engine (N45B20S)

  1. Specifications
  2. Overview, problems
  3. Performance tuning

N45B20 Specs

Manufacturer BMW Plant Hams Hall
Also called BMW N45
Production 2006-2007
Cylinder block alloy Aluminum
Configuration Straight-4
Valvetrain DOHC
4 valves per cylinder
Piston stroke, mm (inch) 88 (3.46)
Cylinder bore, mm (inch) 85 (3.35)
Compression ratio 11
Displacement 1997 cc (121.9 cu in)
Power output 130 kW (177 HP) at 7,000 rpm
Torque output 210 Nm (155 lb·ft) at 4,250 rpm
Redline 7,300 rpm
HP per liter 88.6
Fuel type Gasoline
Fuel system Bosch ME 9.2
Weight, kg (lbs)
Fuel consumption, L/100 km (mpg)

for E90 320si
12.8 (18.4)
6.6 (35.6)

8.9 (26.4)
Turbocharger Naturally aspirated
Oil consumption , L/1000 km
(qt. per miles)
up to 0.7
(1 qt. per 850 miles)
Recommended engine oil 5W-30
Engine oil capacity, L (qt.) 4.5 (4.75)
Oil change interval, km (miles) 7,000-10,000
Normal engine operating temperature, °C (F)
Engine lifespan, km (miles)
-Official information

250+ (155)
Tuning, HP
-Max HP
-No life span loss


The engine is installed in BMW 320si E90

BMW N45B20S engine reliability, problems and repair

N45B20 engine was produced in 2006 in a limited amount. This motor was designed for BMW 320si E90 and replaced N42B20. In some case N45B20S can be considered to be a heritage of M44. It is also used in BMW si models.
The main difference between N45B20 and N42B20 include new crankshaft with stroke decreased by 2 mm. Cylinders diameter was increased up to 85 mm. Engine also got strengthened pistons with compression ratio 11. Iron-cast sleeves were replaced by aluminum sleeves.
In addition new cylinder block is used with bigger valves and renewed camshafts without Valvetronic.
Moreover this engine has one special feature which none of N-series engines has. It includes cylinder head cap made of carbon.
Apart from 2-liter engine N45 series also included N45B16 lighter version. You can learn more about it HERE.
4-cylinder N42 – N43B20 and N46B20 were produced along with N45.
Production of N45B20S continued only one year from 2006 to 2007. Turbocharged straight-4 N13B16 engine turned out to be official replacement of N45 motor.

BMW N45B20 disadvantages and problems

Common malfunctions of this engine are totally equal to N45B16. HERE you can read detailed information about possible problems. It should also be noted that aluminum sleeves are used in N45B20S which results in lack of reliability.

BMW N45B20S engine tuning

N45B20S Chip tuning. Cams

N45B20S is good option for tuning though slightest upgrade can turn out to be rather expensive. Sports camshafts are available on stock. Shirck with characteristics duration 268/260 deg, lift 10.41/9.78 mm is the best bet along with cold air intake and performance exhaust system. When engine management tuning is finally completed your engine will be able to produce approximately 200 HP. Of course, your BMW 320si will perform a better ride. But such modifications can cost you a fortune. If you require more power, you can proceed with cylinder head porting and purchase Schrick camshafts with the following characteristics: duration 272/264 deg, lift 12/11.67 mm. You should note that such upgrades will be more expansive than purchase of BMW 335i with N54 or N55 engines.
You can proceed with the first variant of tuning making your engine produce 200 HP or leave it stock as it is also rather powerful.