BMW M50B25 / M50B25TU Engine

Characteristics

Reliability, problems and repair of the BMW M50B25 engine

BMW M50B25In 1990, to replace the popular inline six BMW M20B25, came a new, much more perfect and powerful, called BMW M50B25 (popularly nicknamed “Plate”), from the new family M50 (the series also included M50B20, M50B24, S50B30, S50B32).

Here a new cast iron cylinder block of 210 mm height with oil injectors was used, intercylinder distance remained the same as on the M20 – 91 mm. The cylinder diameter is 84 mm, cast iron crankshaft has a stroke of 75 mm, the length of the new lightweight connecting rods is 135 mm, the height of the pistons is 38.2 mm. As a result, we have 2.5 liters on 6 cylinders.

The main difference between the M20 and M50 engines is in the cylinder head: in the new engine the head was replaced by a more perfect two-shaft, 24-valve with hydrocompensators (valve adjustment is not threatening). Diameter of inlet valves 33 mm, exhaust valves 30.5 mm. Camshafts with 240/228 phase, 9.7/8.8 mm lift are used.

The timing drive in M50 motors has also changed, now instead of a belt is used a chain, the service life of which is 250 thousand kilometers (usually goes more). In addition, individual ignition coils, electronic ignition system are used, and the size of M50B25 injectors is 190 cc.

There is also an advanced lightweight intake manifold used here.

The engine management system is Bosch Motronic 3.1.

Since 1992, M50 engines received the well-known Vanos intake timing system, and these engines were called M50B25TU (Technical Update). In addition, these engines used new lightweight connecting rods with a length of 140 mm, lightweight pistons with a compression height of 32.55 mm, lightweight valves and single valve springs, instead of double ones on the regular M50.

The control system was replaced by Bosch Motronic 3.3.1.

All power units described above were used on BMW cars with the index 25i.

Since 1995, the M50B25 engine was replaced by a new improved M52B25 engine and in 1996 the production of the M50 series was completed.

Modifications of the BMW M50B25 engine

• M50B25 (1990 – 1992) – base engine. Compression ratio 10, power 192 hp at 5900 rpm, torque 245 Nm at 4700 rpm
• M50B25TU (1992 – 1996) – added Vanos intake timing system, changed connecting rod and piston group, installed other camshafts (228/228 phase, 9/9 mm lift). Compression ratio is 10.5, power 192 hp at 5900 rpm, torque 245 Nm at 4200 rpm.

Problems and disadvantages of BMW M50B25 engines

1. Overheating. M50 engine is prone to overheating and carries it quite hard, so if the motor began to warm up check the condition of the radiator, as well as the pump and thermostat, the presence of air plugs in the cooling system and radiator cap.
2. Trots. Check the ignition coils, most often the problem is in them, as well as candles and injectors.
3. Swimming revs. Often the malfunction is caused by a failed idle valve (COX). Cleaning will help to bring the motor to the senses. If the problem remains, then look at the throttle position sensor (DPDZ), temperature sensor, lambda probe, clean the throttle.
4. M50 Vanos. The problem is expressed in rumbling, loss of power, floating revs. Repair: the purchase of a repair kit vanos M50.

In addition, due to its age and peculiarities of operation, BMW M50 engines suffer from high oil consumption (up to 1 liter per 1000 km), which is not too much reduced after overhaul. Valve cover and oil pan gaskets may leak, leaks through the oil dipstick are not excluded. The expansion tank also likes to crack, after which we get antifreeze leakage. At the same time, periodically problems are caused by the sensors of the camshaft M50, crankshaft (DPKV), the temperature of the coolant and so on.

Despite everything, the BMW M50B25 engine is one of the most reliable power units of the Bavarian manufacturer, and the bulk of the problems are caused by age and style of operation of the motor. And even such engines roll over 300-400 thousand kilometers, and if the motor was used in a sparing mode and adequately maintained, its resource can far exceed 400 thousand kilometers, because not in vain they have received the reputation of millionths of kilometers.

Buying an engine M50B25 is a good choice for swap and subsequent finalization with the use of a turbocharger. Further we will talk about such solutions.

Tuning BMW M50B25 engine

Stroker. Camshafts

The easiest and fastest option to increase power using factory components is to install a long stroke crankshaft (stroker). In M50B25 (Without vanos) the crankshaft from M54B30 with a stroke of 89.6 mm can be installed. From the same motor you need to buy connecting rods, connecting rod liners, repair pistons, injectors, and main liners from M50.

We collect (firmware can be left stock, but it is better to adjust) and drive a 3-liter M50B30, with a power of about 230 hp and compression ratio of 10.

The same power can be obtained by buying Schrick 264/256 camshafts and tuning the stock Motronic. As a result we will get 220-230 hp. We’ll buy a cold air intake, sport exhaust and we’ll get 230+ hp.
The same camshafts on M50B25 3.0 stroker will give about 250-260 hp.

To get maximum power from M50B30, you need to buy Schrick 284/284 camshafts, a six-throttle intake, BMW S50 injectors, a lightweight flywheel, porting of the cylinder head, an equal-length exhaust manifold, and a straight-through exhaust. After tuning, such M50B30 develops about 270-280 hp.

If this is not enough, you can bore the block for 86.4 mm pistons from S50B32 and get a displacement of 3.2. Buy camshafts S52B32 and get about 260 hp.

Vanosny M50B25 can be converted into a 2.8 liter engine by installing a crankshaft with a stroke of 84 mm and connecting rods from M52B28. Together with SIEMENS MS41 firmware it will give +/- 220 hp, compression ratio ~11.

M50B25 Turbo

In the case when the atmospheric motor is not enough or the cost of its implementation is too high, you can organize a turbo version on a 2.5-liter motor. If tuning is supposed to be budget, then Chinese turbo kit based on Garrett GT35 (or other, with brains in a set), your choice. As an option, you can find a used TD05 turbo (or other), weld the manifold, collect all the piping, clamps, boost controller, intercooler and so on. Put everything on the stock piston, pre-installing a thick Cometic cylinder head gasket, 440 cc injectors, Bosch 044 fuel pump, exhaust on a 3″ pipe, EFIS 3.1 (or Megasquirt) brain, tune and at 0.6 bar we get about 300 hp. At 1 bar, ~400 hp.

Something similar can be built by buying a kit M50 compressor and installing it on a stock piston. The output from the compressor will be noticeably lower than the turbo.

Even more power can be obtained by buying and installing a turbo kit on the original Garrett GT35, CP Pistons with 8.5 compression ratio, Eagle connecting rods, ARP bolts, performance injectors (~550 cc). With kits like this you can raise the power to 500++++ hp. Similar projects can be built on a 3-liter stroker.

MOTOR RATING: 5-