Things like great car engines do not just happen. In 1960, when the designers at BMW started work on the Neue Klasse cars, the design process was largely empirical without access to modern computer-aided design tools. There were two major engine design considerations, combustion and balance. Combustion was getting air and fuel into the engine and exhaust gasses out efficiently, whilst balance was managing the combustion in the cylinders to turn it into rotation to drive the road wheels.

Before we delve into the article, we have to note that BMW changed its engine numbering in 1982, which meant that the M05 became the M10 and the M06 became the famous M30. To avoid confusion, we have used the latter designators throughout this article.

THE NEUE KLASSE
For the 1961 Neue Klasse, development for the cylinder head started in 1954, during which 6 different experimental concept engines were made and tested. From these, one head design was based primarily on the all-alloy head from the “M532” 3.2 litre V8 engine introduced in 1954, which powered the 505 Series Baroque Angel saloons and the 501/2/3 and 7 Roadsters. The V8 was a good engine which had established the benefits of a hemispherical-shaped combustion chamber with inclined valves to give a pure cross-flow design for the gasses: inlets on one side, exhausts on the other, with the valves offset along the length of the engine to allow for rocker arms to be driven by a central camshaft.

The real skill was to get the flame front of the burning air/fuel mixture to match the rate at which the piston descended down the cylinder on its power stroke. Detonation (pinking), where the shock wave of the fuel igniting at the spark plug exceeds the burning wave front had to be avoided at all costs. Karl Rech, the engine designer working under chief engineer Von Falkenhausen, found that a flattened hemispherical cross-section with the valves at an angle of 50o to each other and a disfigured heart shape in plan gave the combustion characteristics he wanted. The first 1.5-litre engine with this head design made its debut in 1961, producing 80bhp at 5,700 RPM.

The diagram on the opposite page (1) is a cross-section of the production M30 cylinder head in 1968. It shows the crossflow layout that had been so effective with the V8 “M532” engine in 1954 and the “interference” design, where the valves can intrude into the top of the cylinder when open during part of the four-stroke cycle. This feature allowed the engine’s compression ratio to be changed later by altering the height and shape of the piston crown.

The “interference” feature is still a major consideration when uprating or rebuilding the M30, which we will cover later.

The balance of the new engine was “state of the art”. Square cylinder/ stroke designs, where the cylinder bore is close to the length of the stroke, is a well-accepted design principle which keeps piston speeds down (short stroke) but at the expense of acceleration loads, which are high and hence the loads on the crank journals are also high. The bore for the M30 was 89mm for the three-litre CS range of cars, and the stroke was 80mm. This gave a bore/stroke ratio of 0.9, close to the 1.0 ratio, which is considered ideal for the 3-litre and a little less for the 2.8-litre engines.

Another advantage of these dimensions was that they could give a journal overlap of the profiles (2), which greatly increased the strength of the crankshaft. The main journals of the M30 were 60mm in diameter, and the crank journals were 48mm. So, with a stroke of 80mm, the two journals overlapped by 14mm – as if you’re having a steel rod 14 mm in diameter running the length of the engine.

Rech then took this advantage several steps further. He retained the cylinder centre line spacing of 100mm of the M10 to allow for seven main bearings with the 6-cylinder block since the distance between them allowed for both the big end journal and room for two counterbalance webs, giving the effect that each individual cylinder was balanced on the crankshaft (3).

This 7-bearing crankshaft, which, although complex and expensive to manufacture, has six big end journals at 120o to each other, providing balanced forces at both engine speed and twice engine speed and is inherently smoother than an in-line four-cylinder engine. But there are additional higher-order torsional forces at both four- and six-times engine speed for the six-cylinder, which necessitates the use of a torsional damper on the front of the crankshaft to smooth power delivery and give much-improved reliability. So, a 162mm diameter torsional damper was added to give it a tough engine capable of revving at 6,600 RPM.

As a finishing touch, the crankshaft was forged, and the bearing surfaces were hardened by nitriding, which diffuses nitrogen into the top few millimetres of each journal to create a durable case-hardened surface. Even now, it is rare to find a worn crankshaft, provided it has not been involved in an engine failure.

The M30 also had some other changes compared to its smaller M10 cousin. The first was a change to the shape of the cylinder head, where the combustion chamber was modified from two overlapping flattened hemispheres to three. This created a much-improved swirl to the incoming fuel and air mixture adjacent to the spark plug and an even smoother combustion flame front. The distributor drive, located at the rear of the camshaft on the M10, was moved to the front of the M30 to lower the engine’s overall height and give better accessibility. The external thermostat of the M10 was discarded and the thermostat was fitted to an extended casting on the front of the cylinder head of the M30 instead.

For the 2494 cc (2.5-litre) and 2788cc (2.8-litre) versions of the engine, fuelling was managed by two 32-40 and 35-40 Solex single-choke carburettors, respectively, until the 3.0CSi was introduced with Bosch D-Jetronic fuel injection in July 1971.

PERFORMANCE ENHANCEMENTS
With a rev limit of 6,200 RPM permitted for short periods for road cars, in 1968, BMW delegated the use and further development of the new engine for racing to ALPINA, who soon found that the crankshaft would break at 7,100 RPM. Whilst BMW felt the solution was to increase the strength of the webs and the size of the damper, it was Fritz Indra, ALPINA’s new young engine designer, who lightened the webs, and the rev limit was lifted to 8,200 RPM for racing. ALPINA also discovered that the 300 inclination of the engine caused an oil surge on left-hand corners and developed a compressed gas reservoir which maintained engine oil pressure whenever it fell below a safe level. For the production engine, however, BMW introduced a baffle in the sump to deal with this problem by preventing the oil from flowing away from the oil pump pick-up when cornering (4). For early engines, this was introduced as an upgrade.

In May 1972, with the engine now displacing 3 litres, Bosch D-Jetronic Fuel Injection was introduced to replace the carburettors (5), using induction manifold pressure to control the fuel volume injected. The only cars that didn’t receive this upgrade were those destined for the USA, where D-Jetronic could not meet American exhaust regulations. The D-Jetronic engine produced 200bhp to power both the CSi Coupes and E3Si saloons. However, carburettors were retained for all automatic cars because fuel injection could not cope with the need for “stamp down” acceleration, whereas carburettors could. In late 1973, the D-Jetronic system was replaced by L-Jetronic fuel injection, which used mass airflow to control fuel volume and increased the power to 212bhp, but with a much-improved torque curve.

EVOLUTION AFTER THE E9
In 1977, the engine’s displacement was increased to 3.3 litres and, in 1978, to 3.5 litres using a “3.2” longer stroke crankshaft. This last increase in volume, with the bore at 93.4mm, reduced the spacing between adjacent cylinders to 6.6mm, which led to head gasket failures.

BMW changed the earlier designations of M05 and M06 in 1982 to M10 and M30, respectively, and introduced a major update of the cylinder block to make it narrower and lighter. A further reduction of the cylinder bore to 92mm was used to restore the spacing between cylinders to 8mm. A few years earlier, in 1979, BMW had already introduced the Bosch Motronic fuel injection system. This used a “lambda” sensor, which measured the residual oxygen in the exhaust gasses (which are related to CO and CO2) so that the fuel injected could be optimised for the driving conditions. Further improvements to the Motronic system followed, such as knock-sensors allowing the fuel injected into each cylinder to be individually controlled. The horsepower of the M30 variants was kept at around the 200bhp mark with the emphasis instead on improving torque and response. The last 3.5-litre M30 engine was produced in 1994 for the E32 735i saloon – 25 years after the first M30 had entered production in 1969.

REACHING THE LIMITS
For the purist, the most significant change to the M30 design came in 1978, although for some, the change is not considered part of the M30 history. By 1972, the Motorsport Team, with the help of ALPINA, had developed the single overhead camshaft engine to produce 333bhp at 8,000 RPM for their team cars. In 1973, this had increased to 370bhp, which was considered the safe, reliable limit for the single camshaft design. So, in 1974, BMW Motorsport introduced a twin camshaft 24-valve cylinder head for fitting to the M30 block. Its design was derived directly from the 16-valve twin overhead camshaft cylinder head used by BMW Motorsport for their Formula 2 racing engines.

While the principles of the M30 block were retained, the twin camshafts required a different drive system from the crankshaft—a chain to an intermediate gear and then a gear train to the camshafts themselves. A Kugelfischer mechanical pump injected fuel directly into separate induction trumpets for each cylinder controlled by a slide throttle, and the inlet and outlet ports to the combustion chambers were “Siamesed” to fit two inlet ports and two outlet ports into the limited cylinder spacing of 100mm.

This first Group 2 race engine, designated M49/2 (6), produced 440bhp at 8,500 RPM. However, under pressure from other manufacturers competing in touring car racing, twin camshaft engines were excluded from Group 2 racing in 1975 unless they were used in series-production road cars. So, the BMW Motorsport Team delegated the use of the single camshaft race engines to ALPINA and Schnitzer for European Group 2 races and used the twin camshaft engine M49/3, now producing a reliable 470bhp, for the World Championship of Makes Group 5 (up to 3 litres) races in Europe and in America for the IMSA Camel GT Championship. The USA had become an important market for BMW road cars, and the IMSA series was seen as a way of bringing BMW coupes to the attention of the American public, which the BMW North America Team achieved in considerable style.

The M49/3 had one last throw of the dice – turbocharging. In the 1975 World Championship of Makes, the BMW Motorsport team could not outrun the turbocharged Porsche 935 in the “3 to 6-litre Group 5” class. So, they handed over a team car to Joseph Schnitzer to add a turbocharger (7). It required significant changes, but the original “M30 block” and overhead twin cam design remained unaltered. Mounted vertically, the engine produced 750bhp, and the team car, chassis number 2275981, raced first at Silverstone in May 1976. It subsequently became the Frank Stella Art car at Le Mans in June and finally participated in the Dijon 6 Hour in September. However, the car did not finish in any of the three races because the transmission could not handle the power. It was, however, a fitting swansong for the competition life of the “M30” – starting with 180bhp in 1969 and ending with 750bhp in 1976.

PART 2
Part two will be available in the next edition. In it, we will provide you with a comprehensive understanding of the M30 engine’s intricate design and performance enhancements over the years by covering the individual components in detail, including the block, pistons, oil pump, and crankshaft.