BMW’s first 12-cylinder engine

Posted on November 17, 2012 at 8:05 pm

In September 1986, a magazine in Europe informed its readers: “BMW will be opting for an aero engine-style design. That means most engine systems on the 12-cylinder 7-Series model, which is due for market release in June 1987, will be duplicated. There will even be two lambda sensors. And even if half the engine capacity failed, for some reason, speeds of over 200 km/h would be possible even on just six cylinders.”

Last but not least, BMW’s development chief at the time was quoted as saying: “if the engineers wanted to go for nothing but the best of everything, we didn’t try to stop them.”

The rumour mill was rife with speculation about what appeared to be the German carmaker’s most advanced engine.

Another story claimed that ‘BMW is doing everything it can to promote a sense of exclusiveness and cachet. They even want the licensing authorities to allow them to state the performance not in figures but in words – to the effect that the engine is appropriate in power and performance for the requirements of the vehicle’.

By February 1987, BMW finally put an end to the speculation and released the technical specifications of a new 12-cylinder engine which it would offer with the 750i. The engine, which had been designed completely from scratch, would develop 300 bhp from a displacement of 5 litres. It was hardly surprising that the M70, as the engine was designated, had refinement, low noise levels and excellent balance between performance and fuel consumption which set new benchmarks in engine design during that era.

The V12 engine was first installed in the 750i and then in 1989, it was also offered in the 850i (below)

The 12-cylinder engine – six cylinders on each side in a vee configuration – was displayed for the first time at the Geneva Motorshow that year. Its smoothness was illustrated by a picture showing coins balanced on the engine block which remained upright even when the engine was running. It was the first 12-cylinder engine from a German manufacturer to appear in production form after World War II.

The all-alloy engine set a new benchmark with an overall weight of 240 kgs and its 300 bhp output was matched by maximum torque of 450 Nm at 4100 rpm. The two cylinder banks were positioned at an angle of 60 degrees and their main dimensions were similar to those of the 2.5-litre engine used in the 325i, including a bore of 84 mm. Centrally-positioned spark plugs, within compact dimensions had shorter flame paths, ensuring virtually complete mixture combustion. The absolutely identical cylinder heads had very narrow valve angles and vertical inlet ports. Like the pistons, they were designed to ensure optimum cylinder charging and thus high internal efficiency.

Needless to say, the engine gave the new 750i impressive performance with a top speed of around 270 km/h. However, in agreement with other vehicle manufacturers and taking into account the tyre capabilities of the time, the top speed of the car was electronically-limited to 250 km/h.

V12 engine in the latest generation of 7-Series has larger displacement than the original one introduced 25 years ago

In July 1994, the meteoric career of the first 12-cylinder BMW 7 Series model drew to a close. Around 50,000 cars with the engine had been sold worldwide (almost one in six 7-Series models). It was also used in the 850 coupe and a powerful prototype was developed for a model that was designated ‘M8’ which was never approved for production.

25 years after the first 12-cylinder engine was installed in a production BMW, there continues to be a 12-cylinder option in the current 7-Series. Besides a larger displacement of almost 6 litres, it has TwinPower Turbo technology, direct petrol injection and Double-Vanos continuously variable camshaft timing and develops 544 bhp with 750 Nm.

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By Motor Trader Editorial Team

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