BMW M50B25 / M50TUB25 Engine


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

M50B25 / M50TUB25 Specs

Manufacturer  Munich Plant
Also called BMW M50
Production 1990-1996
Cylinder block alloy Cast iron
Configuration Straight-6
Valvetrain DOHC
4 valves per cylinder
Piston stroke, mm (inch) 75 (2.95)
Cylinder bore, mm (inch) 84 (3.3)
Compression ratio 10.0
10.5 (TU)
Displacement 2494 cc (152.2 cu in)
Power output 141 kW (192 HP) at 5,900 rpm
141 kW (192 HP) at 5,900 rpm (TU)
Torque output 245 Nm (181 lb·ft) at 4,700 rpm
245 Nm (181 lb·ft) at 4,200 rpm (TU)
Redline 6,500 rpm
HP per liter 77
Fuel type Gasoline
ECU Bosch Motronic 3.1
Bosch Motronic 3.3.1 (TU)
Weight, kg (lbs) 198 (436)
Fuel consumption, L/100 km (mpg)
-City

-Highway
-Combined
for E36 325i
11.5 (20.45)
6.8 (34.6)

8.7 (27)
Turbocharger   Naturally aspirated
Oil consumption , L/1000 km
(qt. per miles)
up to 1.0
(1 qt. per 750 miles)
Recommended engine oil 5W-30
5W-40
10W-40
15W-50
Engine oil capacity, L (qt.) 5.75 (6.0)
Oil change interval, km (miles)  7,000-10,000
(4,500-6,000)
Normal engine operating temperature, °C (F) ~90 (194)
Engine lifespan, km (miles)
-Official information
-Real


400+ (250+)
Tuning, HP
-Max HP
-No life span loss

1000+

~200-220
The engine is installed in BMW 325i E36
BMW 525i E34

BMW M50B25 engine reliability, problems and repair

Popular 6-cylinder BMW M20B25 engine was replaced by new powerful and upgraded version of BMW M50B25 motor in 1990. It belonged to new series of engines including M50B20, M50B24, S50B30 and S50B32. The main difference between M50B25 and M50B20 is the fact that new version is equipped with larger pistons (3.3″/84 mm) and crankshaft with extended stroke (2.95″/75 mm). The height of cylinder block is the same. It is 210.7 mm.

The main difference between M20B25 and M50B25 is in their cylinder head. New engine has improved and upgraded cylinder head with 24 valves and hydraulic lifters. Adjustment of customization of the valves is not necessary. Diameter of inlet and exhaust valves is 33 and 30.5 mm respectively. Specifications of M50B25 camshafts are as follows: duration – 240/228 deg, lift – 9.7/8.8 mm.

Timing belt was replaced by timing chain which made it possible to increase the level of duration and lifespan up to 150,000 miles (250,000 km) of mileage. At the same time new engine is additionally equipped by individual ignition coils, lightweight pistons and connecting rods 135 mm long. The size of M50B25 injectors is 190 cc.

In 1992 engines were improved significantly with the help of system of variable valve timing on Vanos inlet valves. From that time engines got their new name. They were called M50TUB25 where TU stands for “Technical Update”. The length of M50TUB25 connecting rods was 140 mm.

The given engine was mainly used in BMW autos with 25i index.

In 1995 M50B25 engine was replaced by a new one. M52B25 motor turned out to have better characteristics. Nevertheless production of M50 series was stopped in 1996.

BMW M50B25 engine modifications and differences

1. M50B25 (1990 – 1992) is basic modification of engine. Specifications are as follows: compression ratio – 10, power – 192 HP at 5,900 rpm, 245 Nm of torque at 4,700 rpm.

2. M50TUB25 (M50TU) (1992 – 1996) is a new version of engine equipped by updated system of variable valve timing on Vanos inlet valves and new camshafts with the following specs: duration 228/228 deg, lift – 9/9 mm. Specifications are as follows: compression ratio – 10.5, power – 192 HP at 5,900 rpm, 245 Nm of torque at 4,200 rpm.

BMW M50B25 engine problems and drawbacks

1. Overheating. Overheating is one of the most common problems when it comes to M50 engine. If you notice this malfunction, you are supposed to check radiator first. At the same time it can result in problems with pump and thermostat. Examine cooling system in order to prevent occurrence of airlocks.

2. Problems with ignition. Proceed with regular checks of ignition coils. Don’t forget about spark-plug and fuel injectors.

3. RPM floating, rough idling. Such problems usually occur due to malfunctions of idling valve. Cleaning is one way to fix this problem. If malfunction is not eliminated, throttle position sensor (TPS), temperature sensor, lambda sensor may come in handy. You can also try and clean throttle body.

At the same time you should also keep in mind that BMW M50 engines have additional problems such as increased motor oil consumption. This rate can be increased up to 1 liter per ever 600 miles (1,000 km) of mileage. Even major overhaul will not prevent from such problem in future. Motor oil can leak through gaskets as well as through dipstick. Expansion tank can also be damaged from time to time which can lead to coolant leak.

Despite the fact that BMW M50B25 engine is considered to be one of the most reliable motors of major Bavarian automaker, biggest part of all malfunctions result in wear-out and age of motors. The average lifespan of these engines is approximately 180,000 – 250,000 miles (300,000 – 400,000 km). If you use it properly, it can be even longer.

M50B25 engine are perfect for Swap as well as further upgrades and tuning suing turbocharger. And here is why.

BMW M50B25 engine tuning

M50B25 Stroker. N/A. Cams upgrade. ITB.

The fastest and easiest way to upgrade your engine is to install long stroke crankshaft (Stroker). It will let you increase capacity of motor up to 2.8-3.0 liters. M54B30 crankshaft with 89.6 mm stroke will be the best bet for M50B25 No Vanos engine. You should also buy connecting rods, connecting rod bearings, repair pistons, fuel injectors (All from the M54B30) and indigenous liners (M50B25).

When the assembly is finally over, you will benefit from 3-liter engine with 230 HP and 10 compression ratio. You can leave stock ECU. However you are recommended to tune it in accordance with new changes.

There is another way to obtain the same power. You should get rid of stock camshafts and buy new Schrick 264/256. In this case you should also proceed with stock Motronic tuning in order to benefit from engine with 220-230 HP. Cold air intake and sport exhaust will make it possible to upgrade your engine up to 230+ HP.

The same camshafts installed on M50B25 3.0 Stroker will also give about 250-260 HP.

If you want to get maximum power from your 3-liter engine, you need to purchase Schrick 284/284 camshafts, individual throttle bodies (ITB), BMW S50 injectors, light-weight flywheel, proceed with cylinder head porting and buy straight exhaust manifold. When the tuning is over your M50B30 ITB will be with up to 270-280 HP.

If you feel like 3.0-liter engine is not enough for you, cylinders can be increased up to 84 mm. At the same time you need to buy S50B32 pistons and camshafts. They will turn your engine into 3.20 liter Stroker with more than 260 HP.

M50TUB25 Vanos engine can also be upgraded up to 2.8-liter motor. You need to install 84mm stroke crankshaft, 135 mm connecting rods (All from the M52B28) and stock pistons. Such improvements will provide you with 220 HP and 11 compression ratio in combination with SIEMENS MS41 ECU.

M50B25 Turbo

If you feel like atmospheric engine is not able to meet your requirements and needs or if you can’t afford such upgrades, you can certainly benefit from turbocharge. Those who are not ready to spend thousands of dollars will certainly take the advantage of Garrett GT35 turbo kit (not original) or any other turbo package which comes with ECU. It should be installed on stock piston. You will also need 440 cc injectors, Bosch 044 fuel pump, Cometic head gasket and performance exhaust systems (3 inch). ECU Megasquirt should be customized so that the engine provides 300-320 HP when the level of pressure is 9-10 psi/0.6-0.7 bar. When this rate goes up to 15 psi/1 bar, engine will reveal its potential along with 400 HP and you will be able to accelerate up to 60 mph (100 kmh) in 5 seconds.

If you want to get even more impressive results, you need to decrease of compression ratio down to 8.5. This is possible with the help of CP/Wiseco forged pistons or any other pistons which have the same characteristics. You will also need Eagle connecting rods, ARP studs and installation of the full Garrett GT35 turbo kit. In this case you are recommended using 550 cc injectors. Such set of tuning and spare parts will make it possible to benefit from engine with 500 HP which is rather impressive.

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