The BMW M50 is a straight-6 DOHC petrol engine which was produced from 1990 to 1996. It was first released in the E34 520i and 525i to replace the M20 engine and the new E36 320i and 325i. In September 1992, the M50TÜ "technical update" (Technische Überarbeitung) introduced BMW's use of Variable Valve Timing (called VANOS) to its engines. The S50 was introduced in 1992 as a high-performance variant of the M50, which powered the E36 M3 and Z3 M. The M50 began to be phased out following the introduction of the M52 engine in 1994.
Design The M50 is pivotal in the history of BMW inline-six engines, as it slowly replaced the decades long run of both the 'Little-Six' M20 and 'Big-Six' M30; marrying the best qualities of both engines into a revised, electronically integrated and more modern package. The M50 is based on the design of the M20 and received many upgrades from its predecessor; primarily introducing a dual overhead camshaft valvetrain (DOHC) with four valves per cylinder and a redesigned engine block.
Compared to the M20, the M50's block is taller and contains oil passages which feed the cams directly. The pistons are also lighter than the M20's, which offsets the added weight of the block. Borrowed from the design of the M30, the M50 is now chain-driven (as opposed to the belt-drive used on the M20) and inherited a crankshaft-driven oil pump. The new head contained a coil-on-plug ignition, a knock sensor and a completely redesigned and more streamlined high-flow intake manifold and is the final inline-six BMW engine to not include any variable valve timing. Like the final iterations of the M20, the M50 employs multi-point electronic fuel injection and likewise uses an iron block with an aluminum alloy head. The redline remained untouched. The location of the oil pan (sump) varies according to the model the M50 is installed in. It is in the front on the E34 5 Series (not unlike the M20), whereas it is in the rear on the E36 3 Series. The iron engine block, healthy output and relatively simple design make the M50 a popular choice for enthusiast tuning, forced induction and engine swaps.
A new upgraded Bosch Motronic 3.1 engine management system introduced OBD-I compliance, which allows the engine to interface easily with modern diagnostic and tuning tools by way of a 20-pin connector found under the bonnet. Despite the different shape, it is electrically identical to a regular OBD-I port, and a passive cable is all that is needed to use standard tools. However, the sensors and other electronics remain relatively simple; as no version of the M50 contained the now-ubiquitous CANBUS communication protocol and was not introduced in until its successor, the M52. Instead, each piece of engine data is polled directly from the engine management system on their own lines.
Models EngineDisplacementPowerTorque YearsM50B20 at 6,000 rpm at 4,700 rpm1990-1992M50B25 at 6,000 rpm at 4,700 rpm
M50B20
The M50B20 was introduced with the 1990 520i. It has a bore of , a stroke of and produces . The compression ratio is 10.5:1.
Applications: 1990-1992 E34 520i 1991-1995 E36 320i
M50B25 The M50B25 was introduced with the 1990 525i and 525ix. It has a bore of , a stroke of and produces at 6,000 rpm and at 4,700 rpm. The compression ratio is 10.0:1.
Applications: 1990-1992 E34 525i, 525ix 1991-1992 E36 325i, 325is
M50TÜ
In order to meet the brand-new Euro 1 emission standard, BMW phased out the M50 with the release of with the M50TÜ in September of 1992. The largest notable change was the introduction of Variable Valve Timing (denoted as VANOS by BMW) on the inlet camshaft; the first of any BMW engine to do so. This had the effect of lowering fuel consumption and flattening the torque curve, which allowed for marginally faster acceleration and better engine response. The engine head was thus redesigned to accommodate for the electronically controlled but hydraulically activated VANOS solenoid; and gives the head a distinctive 'bump' on one side, which makes it easily distinguishable from the M50 at a glance.
In order to accommodate for the new VANOS system, a new Bosche Motronic 3.3 engine management system was introduced; which like the M50, was also OBD-I compliant - with a round 20-pin connector continuing to live under the bonnet. Despite these differences, the M50 and M50TÜ are extremely similar and most of their parts are interchangeable; with many upgrades or modifications are identical processes on both. The initial design for the M52 is also very much akin to the design of the M50TÜ, with many of its differences mainly lying in its engine management system and the inlet manifold. The M50TÜ also is the final non-M BMW engine to have a cast-iron block for worldwide use, and is heavily coveted by enthusiasts who enjoy a highly stable block which is famously resistant to warping for forced-induction modifications - although the North American market kept the cast-iron block for the original release of the M52 due to high sulfur content in their fuel. The pistons were altered to receive longer connecting rods and thus a raised wristpin, which allowed for lower friction against the cylinder walls and for an overall lighter piston assembly. The head received similar minor changes; as the valves springs were changed to a shorter, conical design to minimise weight transfer within the head.
The VANOS system proved to be extremely effective, and was slowly introduced into other engines over time. The first V8 to receive VANOS was the M62TÜ, and the first four-cylinder unit with VANOS was the N42 in 2001. VANOS would continue to develop and contrary to later designs, this initial iteration of VANOS lives on only one camshaft and is purely binary, being on or off instead of the more modern 'Dual-VANOS' systems which live on both camshafts and have continuously adjustable timing found in engines starting with the M52TÜ or the worldwide-spec S50B32.
Models EngineDisplacementPowerTorque YearsM50B20TÜ at 5,900 rpm at 4,200 rpm 1992-1996M50B24TÜ at 5,900 rpm at 4,200 rpmM50B25TÜ at 5,900 rpm at 4,200 rpm
M50B20TÜ A version was introduced in 1992. It produces at 5,900 rpm and at 4,200 rpm. The compression ratio was raised to 11.0:1.
Applications: 1992-1994 E36 320i 1992-1996 E34 520i
M50B24TÜ This is a engine used in the Thailand and Oceanian markets (excluding Australia and New Zealand). It is based on the M50B25TÜ with the stroke reduced to and produces at 5,900 rpm and at 4,200 rpm. The compression ratio is 10.5:1.
Applications: 1993-1995 E36 325iA/2.4 1992-1996 E34 525iA/2.4
M50B25TÜ A version was introduced in 1992. It produces at 5,900 rpm and at 4,200 rpm. The compression ratio was increased to 10.5:1.
Applications: 1993-1995 E36 325i, 325is 1992-1996 E34 525i, 525ix
M50B30TÜ concept In 1993, BMW Individual created a concept of BMW E34 530iX called Enduro Touring. Only one car was produced, having an up-sized variant of M50B25TÜ engine. Bore and stroke was increased and the total displacement of 3.0 was achieved. The power and torque both increased to and respectively.
S50
The S50 is the high-performance version of the M50 which was used in the E36 M3 and worldwide-spec Z3 M, replacing the four-cylinder BMW S14 engine used in the E30 M3. Like the M50, the S50 has an iron block and aluminum head and a DOHC valvetrain with four valves per cylinder. In the North American market, a less powerful variant called the "S50B30US" was used, which shares more in common with the regular M50 engine than the other S50 versions.
S50B30 The S50B30 was used in most countries, except for the North American market and produces , has a bore of , a stroke of and a compression ratio of 10.8:1. The redline is 7,200 rpm. The S50 has an individual throttle body for each cylinder, single-VANOS (variable valve timing on the intake camshaft) and Bosch Motronic M3.3 engine management and redesigned intake and exhaust systems.
S50B30 (M3-R) In 1994, a variant of the S50B30 was created by BMW Australia in partnership with Frank Gardner Racing in Queensland as a limited homologation M3-R for the Australian GT Production Car Championship, being the most powerful of all official S50 variants - rated at . Only fifteen examples were made, with four used on the track and the remaining eleven were sold to the public. They were honed in with AC Schnitzer camshafts, optimised exhaust ports, a more violent tune and a redesigned cold-air intake. Given that all examples were for the Australian market, this is one of the very few BMW engine variants to be exclusively found in only right-hand-drive models.
S50B30GT A homologation special "M3 GT" model was introduced in 1994 with a new engine based on the worldwide-spec S50B30, producing an increased by way of a more aggressive tune, new camshafts and a redesigned sump and oil pump.
S50B30US In the North American market, the 1994-1995 model years of the E36 M3 are powered by the S50B30US, a engine which produces . This engine is more closely related to the standard M50 engine and has the same compression ratio as the M50B25TÜ, but uses a different camshafts, crankshaft, connecting rods, and pistons. The bore is , the stroke is and the redline is 7,000 rpm.
The S50B30US motor was created as a compromise to make the E36 M3 a reality in the United States. Unlike in Europe, the E30 M3 was considered a business failure in America. American customers did not see the value proposition of this vehicle compared to a 325i. Due to this, E30 M3s sold poorly in the United States with just over 5,000 units sold. For comparison, the 325i sold just under 350,000 units. Because of this, BMW of North America planned on retiring the M brand in the US and with it any plans to bring the E36 M3 to America. This was until an editor for the BMW Car Club of America, Bob Roehmer, encouraged BMW CCA members to mail BMW of North America letters asking them to bring the car to the United States. Many BMW CCA members pledged to buy an E36 M3 if it was brought to the United States at a reasonable price. To meet this caveat, Erik Wensberg, the manager of the BMW M Brand in North America, decided to remove the European spec S50 motor and replace it with a BMW M Division-tuned M50 variant. This motor would become the S50B30US and would only be found in American spec E36 M3s.
In 1996, the S50B30US was replaced by the BMW S52 engine (in the United States and Canada only). This motor was a derivative of the M52, and while it maintained the same 240 horsepower as the S50B30US, it gained of torque and increased displacement from 3000cc to 3200cc.
S50B32 In 1995, the S50B32 replaced the S50B30 in worldwide markets. Power output increased to and the displacement increased to , due to an increased stroke of and a slight increase in bore to . The S50B32 introduced the first Dual-VANOS system (variable valve timing on both camshafts) and was continuously adjustable unlike the binary system found on the M50TÜ and a secondary oil pick-up was added. The compression ratio is 11.3:1 and the redline is 7,600 rpm. Engine management also got upgraded to the Siemens MSS50, with 3 knock sensors.
Models EngineDisplacementPowerTorque YearsS50B30 at 7,000 rpm at 3,500 rpm 1992-1995S50B30 (M3-R) at 7,200 rpm at 3,500 rpm1994S50B30GT at 7,100 rpm at 3,900 rpm 1994-1995S50B30US at 6,000 rpm at 4,250 rpm S50B32 at 7,400 rpm at 3,250 rpm 1995-2000
S50B30 Applications: 1992-1995 E36 M3 (except for U.S.)
S50B30 (M3-R)
1994 E36 M3-R (Australia only)
S50B30GT Applications: 1994-1995 E36 M3 GT Coupé
S50B30US Applications: 1994-1995 E36 M3 (U.S. only)
S50B32 Applications: 1995-1999 BMW M3 (E36) (except Canada and the United States) 1996-2000 BMW M Coupé and M Roadster (except Canada and the United States)
See also BMW engines
Notes
References