The BMW S38 engine is a high-performance six-cylinder engine developed for BMW sports cars and used from 1986 to 1995. The engine is characterized by its powerful design and is intended for sports cars such as the BMW M5 and special versions of the M-series. Its roots go back to the M88 engine, from which the S38 inherits design features and a sporty spirit.
The S38 comprises three main versions:
- S38B35 (1986-1989)
- S38B36 (1989-1992)
- S38B38 (1992-1995)
Each of these versions differed in displacement, power and design features that allowed BMW to achieve ever-increasing performance.
Characteristics of the S38B36 engine (3.6 liters)
| Characteristics | Value |
|---|---|
| Power, hp | 315 |
| Fuel type | Petrol |
| Volume, cm³ | 3535 |
| Maximum torque, N-m | 360 at 4750 rpm |
| Fuel consumption, l/100 km | 11.9 |
| Engine type | Row, 6-cylinder |
| Cylinder diameter, mm | 93.4 |
| Number of valves per cylinder | 4 |
| Maximum power, hp/rpm | 315 at 6900 rpm |
| Compression ratio | 10 |
| Piston stroke, mm | 86 |
Features of the S38B36
The S38B36 features a ceramic catalytic converter and exhaust air injection system to reduce emissions when starting a cold engine. This version was popular in BMW models such as the BMW M5 E34 and BMW M5 Cabriolet E34.
Characteristics of the S38B38 engine (3.8 liters)
| Characteristics | Measurement |
|---|---|
| Power, hp | 340 |
| Fuel type | Petrol |
| Volume, cm³ | 3795 |
| Maximum torque, N-m | 400 at 4750 rpm |
| Fuel consumption, l/100 km | 12 |
| Engine type | Row, 6-cylinder |
| Cylinder diameter, mm | 94.6 |
| Number of valves per cylinder | 4 |
| Maximum power, hp/rpm | 340 at 6900 rpm |
| Compression ratio | 10.5 |
| Piston stroke, mm | 90 |
Features of the S38B38
The S38B38 has increased cylinder size and piston stroke compared to the previous version. In the international market it came with an Emitec metal catalyst, which reduces engine weight and increases exhaust flow. The fuel injection control system was also changed: the initial version of Bosch Motronic 1.2 was replaced by the more modern Motronic 3.3.
Reliability, engine design BMW S38
A new sporty engine called S38B36 was designed especially for the 1988 BMW M5 E34. The engine was based on the M88/3 (S38B35), with the related M30B34 series, the S38 has less in common (although with a certain degree of fanaticism, the M30B34 can be converted to the S38). The M88/3 cylinder block was fitted with a lightweight forged crankshaft with a piston stroke of 86mm (it was 84mm) and 12 counterweights. The cylinder diameter remained unchanged (93.4 mm), the pistons were modified with a compression height of 31.5 mm and compression ratio of 10, and the connecting rods were 144 mm long.
The cylinder head of the BMW S38 is a twin-shaft 24-valve cylinder head with mechanical tappets. The valves are adjusted as necessary, the clearance on cold 0.28/0.33 mm. Parameters of camshafts S38B36: phase 264/110, lift 10.7 mm. Inlet valves are 37mm, exhaust valves are 32mm. On the inlet is installed manifold with variable geometry and, of course, 6 throttles, one for each cylinder, the diameter of each throttle – 46 mm. The injectors have a capacity of – 270 cc. The control unit is Bosch Motronic M1.2. Equal-length manifold is used on the exhaust. In the drive of the timing is used a two-row chain, quite reliable.
These innovations allowed to remove the power of 316 hp at 6900 rpm.
Since 1992, the S38B36 engine was modernized: the crankshaft with a stroke of 90 mm and with 12 counterweights, connecting rods 142.5 mm long, cylinder diameter increased to 94.6 mm, new lightweight pistons with compression height of 30.7 mm, compression ratio increased to 10.5, and the working volume reached 3.8 liters.
The S38 cylinder head also underwent modifications: the intake valves increased in diameter to 38.5 mm, the exhaust valves to 32.5 mm, and the intake and exhaust ducts were improved. The camshafts on the S38B38 are 264/108, 10.7mm lift. The intake manifold has been redesigned, throttle plates increased in diameter to 50mm. The exhaust is also new, the control unit is Bosch Motronic DME 3.3.
All this improved the car’s behavior at low and medium speeds and increased power to 340 hp at 6900 rpm.
Production of sporty inline sixes S38 was stopped in 1996, along with the discontinuation of the M5 E34 sedan, and the successor came out in 1998, under the hood of the M5 E39, called S62B50 and had a V8 configuration.
Benefits
Benefits of the S38B36 engine
- Bosch Motronic 1.2 Control System
The S38B36 is equipped with the Bosch Motronic 1.2 control system, which provides high reliability and durability. The engine’s wiring can withstand significant loads and the engine itself is designed for long-term operation. The control system allows fuel economy to be achieved:
- Mixed cycle – 10-12 liters per 100 km
- Highway – 9 liters per 100 km
- City cycle – about 14 liters per 100 km
- Sporty design
The S38B36 is based on the architecture of the M88/3 atmospheric engine to create a powerful and reliable sports motor. The engine features a forged crankshaft with 86 mm piston stroke and 12 counterweights for optimum load distribution. - High performance
The S38B36 motor features 24 valves with twin-shaft mechanical tappets. The intake valves have an increased diameter of 38.5 mm and the exhaust valves 32.5 mm. The design of the intake and exhaust ducts has also been improved, increasing power to 340 hp at 6,900 rpm and allowing the engine to operate consistently at low and mid-range speeds. - Powerful injectors and air delivery system
The engine’s injectors have a capacity of up to 270cc, while the air delivery system and advanced Vanos provide stable and high thrust. This contributes to fast acceleration and stable behavior at high speeds.
Benefits of the S38B38 engine
The S38B38 version has improved performance:
- Power – up to 340 hp at 6900 rpm
- Compression ratio – 10.5
- Torque – 400 N-m at 4750 rpm
- Weight – 151.2 kg
BMW S38
Disadvantages of the S38B36 engine
Despite its many advantages, the S38B36 has its disadvantages, which are important to be aware of:
- Technical issues and breakdowns
Some owners experience crankshaft rotation problems, which can be caused by poorly attached battery terminals or a disconnected ground bus. It is not uncommon for the starter and terminal fasteners to fail, resulting in engine malfunctions. - Cold Start Problems
Cold start instability may be due to a dead battery, ignition system malfunctions, or fuel injection system failures. - Injection system failure
The engine may stall immediately after starting due to faults in the injection system. Vibrations at high speeds are also not uncommon, caused by poorly fastened components or injection system wear. - Wear and failure of the timing system
Wear and tear of timing system components is also a common problem. Over time, cracks may develop in the cylinder block, which often occurs where the bolts are fastened. This increases antifreeze consumption and leads to emulsion in the oil.
Disadvantages of the S38B38 engine
- Cracks in the cylinder block
Cracks can occur at the cylinder block bolt locations, especially when the engine is frequently assembled and disassembled. This increases antifreeze consumption and causes emulsion in the oil. - Overheating
The engine is susceptible to overheating if the radiator is clogged, the pump or thermostat malfunctions. Sometimes overheating can be caused by an air lock in the cooling system.
Engine tuning
S38 Atmo. Stroker
The easiest option to increase the power of the BMW M5 E34 engine without supercharging is to buy Schrick 280/280 camshafts with springs, 440 cc injectors, cold intake, full sport exhaust along with a 6-2-1 manifold and then adjust the brain to the new iron. These conversions will raise the output to 380hp on the S38B38 and 350hp on the S38B36. This is the most urban configuration. Installing a 3.8 intake on the S38B36, and 296/280 camshafts, along with cylinder-head porting and enlarged intake valves up to 39mm, you’ll get about 390hp. The cylinder-head porting, 1mm larger intake valves, and 296/280 camshafts on the S38B38 boosts power to ~420hp.
The next step up in power could be to replace the standard piston with a light forged (95mm) piston for a compression ratio of 12, buy lightweight Carrillo connecting rods, install 304/296 camshafts and a Haltech E11 (or other) brain. You’ll get up to 450hp on the S38B38 and up to 420hp on the S38B36.
In addition to the shafts, you can rock the BMW M5 E34 by installing a stroker kit: crankshaft with a stroke of 98 mm, H-shaped connecting rods, forged pistons with a diameter of 95 mm for the desired compression ratio.
S38 Turbo. Compressor
Instead of the above, you can install a turbine or compressor on a standard BMW M5 E34 engine and get the same 450 hp. For this you will need a classic kit: ARP studs, Cometic cylinder head gasket, receiver, Garrett GT42 with manifold, pips, intercooler, westgate, blouoff, 630 cc injectors, 044 Bosch, 85 mm exhaust, Megasquirt brain. Inflate 0.5 bar and you get under 500 hp on the S38B38 and about 450-470 on the S38B36. Additionally, buying forged pistons for compression ratio of 8.5 and H-beam connecting rods, finalizing the fuel system, you can blow up to 600 hp and more. Similar can be done using a compressor, ready kits will provide about 450 hp on standard pistons.
ENGINE RATING: 5