The BMW Six Cylinder Guide

 

Of all car companies on the planet, BMW has produced the most worshiped six-cylinders. From its DOHC, individual throttle M1 engine to the latest Double VANOS engines, BMW sixes have set the standard. In this article we look at the most important hi-po modern BMW sixes from the ‘70s to present.

BMW SOHC Sixes

BMW’s marvellous sixes kicked off as early as 1933 but the first to employ fuel injection technology was M30 engine, as found in the 1971 BMW 3.0Si sedan and 1972/1973 3.0SCi and 3.0CSL coupes.

The injected M30 has a total displacement of 2986cc (using a larger bore than found in earlier 2.8-litre BMW sixes) and breathes through a SOHC two-valve-per-cylinder alloy head with a chain cam drive. The Si suffix identifies the fitment of D-Jetronic fuel injection - a MAP sensor based electronic system. The Bosch designed injection system gives the Beemer six much improved refinement and the ability to produce 149kW at 5500 rpm with 272Nm of torque at 4300 rpm. Then, in late '76, the D-Jetronic injection system was swapped for L-Jetronic. Output slipped slightly to 146kW but we believe this was due to tightening emission regulations. Note that smaller 2-litre and 2.8-litre fuel injected engines can be found in the first generation BMW 5-series (of 1972) but these aren't as grunty as the 3-litre.

Released side-by-side with the 3.0Si sedan was the European market 3.0Li and 3.3Li. These long wheelbase saloons have the same 146kW L-Jetronic 3-litre as the updated 3.0Si or an optional 3.3-litre version generating about 7kW extra. By 1977, production of the 3.0Si, the coupes and long wheelbase models wound down.

In 1977, BMW released its all-new 7-series (E23 chassis code). The ex-3.3Li L-Jetronic injected 3.3-litre M30 six could be found in the 733i and a slightly smaller capacity 3.2-litre version was sold between 1980 and 1983. A 2.8-litre and 3.5-litre version was also sold during the E23’s lengthy lifespan. Corresponding E24 6-series coupes were offered with a 3-litre six and, in the next couple of years, a 3.2 and 3.5 litre.

On a smaller scale, the M20 BMW engine was released in 2-litre and 2.3-litre capacities for use in the 1977 E21 3-series. The 2-litre version, the ‘baby’ M20B20, uses a belt cam drive, K-Jetronic injection and puts out around 90kW. With a larger bore, the 2.3-litre M20B23 (as found in the sporty 323i) puts out 107kW.

The early ‘80s E30 3-series was absolutely strangled by tightening emission standards. The ‘Eta’ BMW engines were aimed at improving efficiency but the 90kW output of the 323e and 95kW 325e were hardly worth getting excited about. Fortunately, a freer breathing 325i was also offered with a semi-decent 125kW/222Nm.

The ‘80s E28 5-series was also lumbered with mostly below-par Eta engines but the M535i uses a 163kW version of the M30 3.5-litre six. In the updated 5-series, the E34, the hottest performer is the 3.4-litre M30 found in the 535i. This engine is good for 155kW/305Nm. The same engine can be found in the late ‘80s E32 735i.

Interestingly, in 1980, some markets received a 745i model using a turbocharged M30 engine known as the M102. With the same 3210cc internals as other versions, the M102 has low compression (7:1) pistons to accommodate boost pressure from a single KKK turbocharger and air-to-air intercooler. Output is 188kW at 5200 rpm with a strong 380Nm at 2600 rpm. The M102 was followed by the M106 which is essentially a 3.5-litre version with higher compression and less boost. From around 1983 to 1985, this engine matched the output of the smaller M102 but enjoyed greater torque at lower revs.

The First DOHC BMW Six – a Ripper! In 1979, BMW Motorsport stunned the market with its M1 road-going racer. These are amongst the most collectable cars in the world. The M1 uses a M30-based engine displacing 3453cc – but the big difference is the fitment of a DOHC, four-valve-per-cylinder head with tuned-length extractors and individual throttle bodies. A dry sump is also employed. These changes create an engine known as the M88/3. Output is 207kW at 6500 rpm and 330Nm at 5000 rpm. The engine is mid-mounted in the M1 and tied to a five-speed ZF gearbox. Pretty cutting edge in the late ‘70s!

BMW DOHC Sixes

The first six-cylinder BMW engine family to employ DOHC breathing is the M50.

The M50 engine was introduced in the 1989 E34 5-series and E36 3-series. There were two capacities available - 2-litre and 2.5-litre. The M50 retains BMW’s iron block/alloy head formula and carries over the same cylinder spacing as the old M20 but adds the sophistication of a DOHC, four-valve-per-cylinder head and DME M3.1 engine management. The smaller of the M50s, the M50B20 1991cc, uses a 10.5:1 compression ratio to help deliver 112kW at 5000 rpm. The larger M50B25 2.5-litre version (with larger bore and stroke dimensions) has a slightly lower compression ratio but generates an extra 31kW and greater torque.

In 1992, the M50 was updated to include VANOS variable inlet cam timing and more sophisticated DME MS41 engine management. It appears power remained the same but torque and emissions were improved.

Also in 1992, BMW Motorsport released the new generation E36 M3. Powered by a highly tuned, solid lifter version of the M50 – the S50B30 – you’re talking 213kW at 7000 rpm. In 1995, the US market received a version with single VANOS and making 179kW at 6000 rpm.

The M50 was replaced by the M52 during 1994. The M52 series can be found in the E36 3-series, E39 5-series, 1999 E46 3-series and Z3. There were three capacities available – 2-litre, 2.5-litre and 2.8-litre (known as M52B20, M52B25 and M52B28 respectively). At last, BMW ditched its iron blocks in favour of an aluminium block with Nikasil coated bores – a move which helped shave around 30kg from the total engine weight. Note, however, some counties using high-sulphur fuel received an iron block version. All use VANOS variable inlet cam timing. The base M52B20 (as found in the 1994 320i) generates 110kW, the 2.5-litre M52 B25 makes 127kW (as found in the 1995 523i) and the 2.8-litre M52B28 makes 144kW (as found in the 1994 328i).

In 1997/1998, BMW aced the competition with the availability of Double VANOS technology – the ability to infinitely vary inlet and exhaust cam timing. With accompanying changes to the intake manifold, the Double VANOS M52 family of engines make no extra power but improve torque, drivability and emissions. These engines can be found in the 1998 E36 320i and Z3 2-litre, 323i and Z3 2.3 and 328i/528i and Z3 2.8. These engines put out 110kW/190Nm, 125kW/210Nm and 142kW/275Nm respectively.

The M50/52 engine was replaced by the M54 in 2000/2001. The engine was made available in the X5, E46 3-series, Z3 and Z4. The M54 (which still has similarities to the old M20!) uses an aluminium block with cast iron liners. There’s a 2.5 litre version and a large stroke crankshaft creates a 3-litre. Double VANOS and electronic throttle control are also incorporated. The 2.5-litre M54 generates 137kW but, for the 3-litre M54, output is 170kW and 300Nm (on 98 RON fuel).

Today, the 170kW/300Nm spec 3-litre M54 is still used in the X5, X3 and the yet-to-be-replaced E46 series 330Ci coupe/convertible. The E46 3-series coupe/convertible can also be purchased with a 125kW 2-litre or 151kW 2.5-litre (in the 320Ci and 325Ci respectively). The newly released E90 3-series sedan and E60 525i can be purchased with a 2.5-litre six generating 160kW/250Nm while the 330i sedan and E60 530i uses an upsized 3-litre pushing 190kW and 300Nm.

The most potent BMW six is the S54 3.2-litre straight-six, as fitted to the late ‘90s Z3 and Z4 M-Coupe, M-Roadster and current E46 M3. Revving up to a 8000 rpm redline, the S54 boasts individual throttle bodies with Normal and Sport operating settings, Double VANOS (operating over a wider range than other BMW sixes) and a 11.5:1 compression ratio but, unusually, a cast iron block to ensure durability. No surprise to find a huge 252kW at 7900 rpm and 365Nm at 4900 rpm – not bad from an atmo 3.2-litre engine...

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