BMW M50B25TU engine

BMW cars are a symbol of German reliability. These cars are powerful, defect-proof, high quality and finally, they are simply beautiful. This is not least due to the engines they are equipped with. BMW engines are able to demonstrate stunning dynamic performance in extreme conditions, as well as being economical and reliable in everyday operation.

The source of such an impressive result in the efficiency of the finished powertrains is the meticulous quality control of the assemblies and components produced. At all levels.

At the same time, the company’s engineers are constantly working on improving the produced engines and on the introduction of innovations, thanks to which the latest achievements of progress are realized in practice. Thus, at the beginning of the last decade of XX century, the M50B25TU has replaced the common type of power unit M20. It is interesting to analyze in more detail the differences of its device and the advantages that the new unit has received.

M50B25TU engine specifications

Introduced innovations in the M50B25TU engine model compared to the M20 and their effect

The following design changes have been made to enhance dynamic performance while improving engine economy:

• The number of valves in the cylinders.

In the new engine, the cylinder head is equipped with 24 valves – 4 for each cylinder (instead of 2 in the old version of the engine). Moreover, the valves have a new design (diameter of inlet valves – 33 mm.; exhaust valves – 30.5 mm.) and are made of a new alloy, thanks to which they have become lighter by 1.8 times, as well as significantly increased their working life. Of course, the design of the cylinder head has also changed – now it has 2 camshafts. Hydrocompensators have been added to the design, thanks to which it is no longer necessary to monitor the gap, but only to control the oil level in the hydraulic system. A pair of camshafts is driven by a chain with hydraulic tension (instead of a belt in the previous model). The operating life of the chain is 250 thousand kilometers.

• Intake manifold.

In the new engine, attention has been paid to the aerodynamic shape of the intake manifold. Thanks to its near perfection, the engine’s combustion chambers are now filled with air more intensively (i.e. faster), which increases the number of crankshaft revolutions per unit of time and therefore the specific power.

• Ignition system.

Individual ignition coils (one for each cylinder) regulated by the electronic engine management system “Bosch Motronic 3.1” are used here. As a result:

• Engine power figures have been increased.
• Due to better combustion, specific fuel consumption has been reduced.
• The environmental performance of the motor has been improved.

Engine oil usage issues

Engine lubrication is provided by means of forced oil supply to the rubbing elements of the engine by means of a gear-type pump. The pump is structurally located in the oil pan, but to avoid clogging and to improve the operation of this element, a special cleaning filter is installed in the system before the oil inlet to the pump.

What oil is used in M50B25TU motor? And what viscosity to pour the oil? There are several variations of its varieties:

1. 5W-30;
2. 5W-40;
3. 10W-40;
4. 15W-40.

It is not recommended to ask questions about viscosity – it is better to just take care of purchasing oil of appropriate quality. The engine is designed to use the specified range of oil at any temperature (and consequently viscosity). Up to 5.75 liters of oil are present in the engine. At the same time its standard consumption per 1000 km is not more than 1000 gr. It is recommended to change oil every 7-10 thousand kilometers.

The Vanos system

Installation of this system is already a full-fledged tuning. “Vanos” adjusts the position of camshafts at high engine speeds. The fact is that when the number of operating cycles per second passes a certain value, it becomes optimal to open the intake valves a little earlier to more effectively ensure the filling of the combustion chamber with oxidizer (air). To do this, it is necessary (without stopping the movement) to slightly change the position of the camshaft on the intake valves by turning it slightly forward.

The effect is as follows:

• the power increases;
• lowers fuel consumption;
• the ventilation of the combustion chamber is increased.

The principle of operation of “Vanos” is simple: a special sensor constantly monitors the parameters of engine operation. When information is received that the power characteristics do not match the RPM level, an electromagnetic switch cuts off the oil pressure in the hydraulic supercharger, which adjusts the camshaft cam gap and, consequently, the degree of valve opening. As a result, the intake valves open earlier and stay open longer, and the vehicle gains additional power reserves.

The Vanos system consists of:

• hydraulic clamping of the camshaft on the inlet valves;
• oil supply system;
• switch solenoid relay;
• controller.

Stroker

Another option for tuning the M50B25TU engine is to replace the crankshaft with a stroker crankshaft – a long-stroke crankshaft with a larger crank. As a consequence, the piston stroke, engine displacement and compression ratio increase. For example, if the engine in question is fitted with a crankshaft with a piston stroke of 89.6 mm, then:

• engine displacement will increase to 3 liters;
• power will rise to 250-260 horsepower;
• the compression ratio will be closer to 11.

True, you’ll have to make a number of additional substitutions:

• connecting rods;
• connecting rod liners;
• pistons;
• and you’ll need other nozzles.

And if you add a sports exhaust and cold air intake system, you can easily “overclock” the engine (which in the native version produces 192 hp) up to 270 hp!

Summary

The M50B25TU engine is an excellent basic foundation for all sorts of modifications, some of which have been described above. For those wishing to make a turbo M50B25TU, it is also possible:

• install a turbo kit based on the original Garrett GT35;
• use CP Pistons for 8.5 compression;
• Eagle connecting rods;
• ARP bolts;
• injectors (~550 cc).

As a result, the 2.5-liter motor will be able to produce up to 500 hp on the turbine! However, it is worth thinking whether it is necessary, because the base M50B25TU gives out the whole range of power characteristics, which only can be demanded in the city and in highway conditions.

This engine is installed on the following models:

BMW 5-Series (E34)