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The new V8 Power Unit for the BMW M3 - High-speed engine

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The new V8 Power Unit for the BMW M3
High-speed engine
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High-speed engine concept entering a new dimension
The designers and engineers responsible for the new power unit have nevertheless remained faithful to the high-speed engine concept so typical of BMW M. Indeed, they have even raised this concept to an unprecedented level, the new V8 reaching maximum engine speed of 8,300 rpm, a figure so far seen only in motorsport engines and a handful of exotic, hand-built cars. To this day, hardly any engine designer or engineer responsible for a series production engine has dared to enter this terrain.
The high-speed engine concept is however a traditional forte of BMW M GmbH’s high-performance natural aspiration engines, generating enormous power and performance from high engine speeds. This avoids the conventional wisdom of simply increasing the size of the engine or using a turbocharger, often involving an undue increase in weight and fuel consumption.
Through the high-speed engine concept, the engine development specialists at BMW M GmbH thus ensure that the spontaneity of the engine, its instan-taneous response to the driver’s wishes, reflects the great demands made of an M Car and its overall concept. And so, in its performance potential, the development of power, in its dimensions and weight, the V8 power unit is a typical BMW M engine through and through.

Taking Formula 1 as a role model and paving the way through BMW M engineering
A further significant point is that the eight-cylinder boasts all the features and qualities so typical of BMW M, such as double- VANOS, individual throttle butterflies, and high performance engine electronics. At the same time the number of cylinders, the high-speed engine concept and the low weight clearly indicate that the engineers responsible for the new eight-cylinder have been inspired by another eight-cylinder – the unique engine featured in the BMW Sauber F1, the engine currently raced by the Team in the highest realms of motorsport. And indeed, the two power units share a number of features not only in their basic technological principles, but also in their production methods and materials clearly borne out by the transfer of technology from motorsport to series production. One difference, however, will always remain: The BMW M3 is required to offer outstanding performance not only on racing weekends and therefore features a high-performance power unit fully suited for everyday use and reliability on all roads, in all kinds of weather, and in years of tough motoring the world over.

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Twenty per cent more power – a new dimension in driving dynamics
A new BMW M3 must offer one feature in particular: even more power. And this is precisely why the fourth generation of the BMW M3 gives its proud owner about 20 per cent more power than before, the engine churning out a substantial 309 kW/420 hp. In its specific output, the eight-cylinder easily exceeds the benchmark of 100 hp per litre acknowledged as the standard for a particularly sporting and dynamic power unit. But even so, power is not everything. Instead, the dy-namic experience offered by a car is borne out in particular by its acceleration and performance in gear at all speeds resulting also from the weight of the vehicle and the sheer thrust and muscle of the engine.
The engine is an important factor in determining the weight of a car, that is the mass to be accelerated – after all, it is one of the heaviest modules within the car to begin with. So precisely here, the new BMW M3 again sets a new standard with engine weight of just 202 kg or 445 lb, making this V8 one of the lightest eight-cylinder engines in the world.
By comparison, the 294 kW/400 hp V8 in the predecessor to the current BMW M5 weighed 240 kg or 529 lb. So despite the extra power, the new engine is more than 15 per cent lighter. Indeed, it is approximately 15 kg or 33 lb lighter than even the six-cylinder power unit in the former BMW M3. So the extra weight of the two additional cylinders is more than set of by intelligent lightweight technology on the new engine.

High-speed engine concept for superior power and torque in practice
The second factor crucial to driving dynamics, the power and thrust actually conveyed to and by the drive wheels, results from engine torque and the overall transmission ratio. At 400 Newton-metres or 295 lb-ft at 3,900 rpm, maximum torque of the new eight-cylinder is approximately 10 cent higher than the peak torque of the former straight-six, and the engine develops an equally superior 340 Newton-metres or 251 lb-ft at just 2,000 rpm. No less than some 85 per cent of the maximum torque is indeed maintained consistently over a speed range of 6,500 rpm very broad indeed for a sports car engine. This is clearly reflected by the performance characteristics of the new BMW M3 not only offering a supreme standard of dynamic power, but also all the qualities for cruising smoothly on winding country roads or in city traffic.
Last but certainly not least – and indeed quite crucial in terms of overall qualities – the high-speed engine concept with its M-specific features allows use of the optimum transmission and final drive ratios and thus guarantees a perfect rendition of muscle and performance on the road under practical driving conditions.
The effect provided in this way is borne out by a clear example: Whenever a cyclist shifts down on an uphill gradient, he has to turn the pedals faster, but in return he can ride up virtually any hill. Should he, on the other hand, remain in the same gear or even shift up, he will have to pedal harder or even get off his bicycle. And given the same power and muscle, the cyclist able to turn the pedals faster will always be the winner.

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High speed, low weight
The fact remains that more power alone – that is higher torque – is not sufficient to be a winner. And so the BMW M3 outperforms competitors focusing on the torque concept alone, wherever those models require a massively reinforced and, accordingly, heavy drivetrain to convey their extremely high level of torque, since this extra weight and mass must first be accelerated and propelled to a higher speed. The high engine speed concept, on the other hand, enables the engineer to opt for a much lighter drivetrain and choose a far shorter transmission ratio. The other side of the coin is that the M high-speed engine concept is extremely demanding in technological terms: While the former straight-six was still limited electronically to maximum engine speed of 8,000 rpm, the new eight-cylinder exceeds this mark by far, revving all the way to 8,300 rpm. This is indeed the fastest-revving V8 power unit in the world built in numbers going beyond a small model series.
Given this kind of power and such unique technology, the engine of the new BMW M3 shifts the limits of technology in series engine production to a much higher level than before – quite simply because the higher the speed of an engine, the closer you come to the highest limit physically achievable. At a speed of 8,000 rpm, each of the eight pistons covers a distance of 20 metres or almost 66 feet per second – piston speed found until recently only in the exclusive world of motorsport. The conventional wisdom so far was indeed that this kind of speed and the loads exerted on the materials in the process were simply too much for series construction.

Targets in the design and construction process: compact, stiff, light
In developing BMW’s new eight-cylinder power unit, the engineers and other specialists sought to reduce all moving masses to an absolute minimum, focusing above all on the crank and valve drive in their search to ensure minimum rotating and moving masses. Precisely this is why they decided to combine two rows of four cylinders at a V angle of 90° and an off-centre arrangement of 17 millimetres or 0.67´´ to make the entire power unit extremely compact and efficient.
The decision to choose a 90° angle was taken on account of the efficient compensation of mass forces provided by this geometry, serving to minimise vibrations and maximise motoring comfort. By and large, therefore, this specific geometry offers the optimum solution to the conflict of interests resulting from maximum smoothness free of vibrations, on the one hand, and maximum stiffness of all relevant components, on the other.



 
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