The ten-cylinder power unit featured in the BMW M6 may rightly be regard-ed as the most fascinating engine you can imagine in a production car. Launched just half a year ago in the BMW M5, this unique power unit has been thrilling enthusiasts all over the world ever since, of-fer-ing a seemingly never-ending surge of power and performance. Many people see this engine as the “civilian derivative” of the BMW Will-iams-F1 racing unit.
The V10 is reminiscent of BMW’s Formula1 racing engine also in terms of its sound: A bit deeper and more muscular than even in the M5, the V10 featured in the BMW M6 clearly “shouts out” its dedication to motor-sport.
Inspired by the Formula1 power unit.
The V10 featured in the BMW M6 shares both the number of cylinders as well as its high-speed concept with BMW’s Formula1 power unit. This alone guarantees enormous thrust and muscle from high engine speeds, a feature characteristic of all high-performance normal-aspiration power units devel-op-ed and built by BMW M GmbH.
Reflecting this exclusive standard, this top-of-the-range engine is equally
im-pressive in all its specifications: ten cylinders, five liter capacity, 507 horsepower maximum output, 383 lb-ft maximum torque, engine speeds up to 8,250 rpm – a power pack in its purest form.
But at the same time this engine is far more than the sum total of outstand-ing performance data: Barely touching the gas pedal, you will immediately appreciate this high-speed normally-aspirated engine as a typical sports pow-er unit. And at the same time it is perfectly civilized in everyday traffic: Sometimes a luxurious coupe, sometimes a thoroughbred sports car. The M6 offers you the best of both worlds, setting the benchmark in both cate-gories.
Brand-new and offering the best of the best.
The V10 power unit created by the engineers at BMW M GmbH for the M5 and M6 is brand-new from the ground up. In the process of developing this engine, they were inspired by the BMW WilliamsF1 power unit, one of the most powerful engines in the highest category of motorsport. As their second consideration, they focused on M-specific fea-tures in standard production such as double-VANOS, individual throttle but-terflies, top-performance engine electronics, and oil supply with centrifugal force control.
In principle there are three options to achieve optimum power and performance in engine construction: To make the engine larger, obtaining higher torque in the process, to boost engine output by means of a turbocharger or compressor, or to increase engine speed by means of the high-speed en-gine philosophy.
Power is more than just a number.
This means that on the road, power and performance is more than just an impressive horsepower rating. Rather, what really counts is a car’s behavior when accelerating and its driving dynamics. And this depends on the thrust and muscle actually generated by the drivetrain as well as the weight of the car. The thrust going to the drive wheels, in turn, is a result of engine torque and the overall transmission ratio. The high-speed engine concept, therefore, allows the right transmission and final drive ratios, guaranteeing impressive performance also in everyday motoring.
Given these basic laws of physics, we find huge differences between vari-ous engines, even when on paper they have the same output. A large-vol-ume engine, for example, has the disadvantage of both extra weight and larger dimensions leading to higher fuel consumption. A turbocharged en-gine likewise consumes more fuel and lacks spontaneity that is the instan-taneous response of the engine to the driver’s wishes.
The high-revving concept – the perfect answer.
This leaves the third option: the compact, fast-revving normal-aspiration
power unit. For traditional reasons alone the engineers at BMW M acknowledge this concept as the ideal solution, increasing engine output
and performance by an appropriate increase in engine speed. The fact remains, however, that the high-speed engine concept is far more demanding in technological terms, making it a greater challenge requiring more sophi-sticated solutions. Reaching engine speeds of 8,250 rpm, the V10 enters a speed range until recently reserved to thoroughbred racing cars alone.
Formula 1 technology for the road.
Featuring qualities of this kind, the new V10 raises the limits to technology in series engine production to a higher standard never seen before. A comparison clearly shows what this means in terms the loads and forces acting on the various materials: At a speed of 8,000 rpm, each of the 10 pistons co-vers a distance of some 20 meters a second. Revving at 18,000 rpm in the BMW WilliamsF1, piston travel is actually 25 meters per second. But while durability is merely a relative factor in motorsport, a BMW M engine must last the same long life as the car itself – in all kinds of weather, under all traffic conditions, and with that typical M style of motoring.
507 horsepower for a new world of driving dynamics
The fast-revving ten-cylinder develops maximum output of 507 horsepower at 7,750 rpm. But compared with its output and performance it remains a lightweight athlete weighing just 240 kg or 529 lb. When it comes to output per liter, on the other hand, this engine is definitely a “heavy” player. The ten-cylinder easily achieves the magical limit of 100 hp per liter, with speci-fic output comparable to that of a racing machine.Only engine speed can really bring out power and torque.
Maximum torque of 383 lb-ft comes at 6,100 rpm. But the ten-cylinder develops 332 lb-ft from just 3,500 rpm, with 80 per cent of the engine’s maximum torque offered consistently throughout a wide range of 5,500 rpm.This alone places the BMW M6 with its high-speed engine far above the com--petition, with virtually all other models focusing on torque alone provided by larger engine capacity and/or turbocharging. A further drawback with oth-er models is that they require a significantly reinforced and, as a result, very heavy drivetrain to convey their extremely high torque, thus suffering from extra weight and mass which consistently has to be accelerated and slowed down. By contrast, BMW’s compact V10 with its high-speed concept bene-fits from a far lighter drivetrain with a much faster gearshift.
A good example is that of a cyclist riding up a hill. Shifting down a gear, the cyclist will have to turn the pedals faster, but is able, in return, to take virtually every grade. Should the cyclist remain in the same gear or even shift up, on the other hand, the choices would be to either put more strength into the pedals or, quite simply, get off the bicycle. Taking two cyclists absolutely equal in their strength and stamina, the winner will always be the cyclist able to turn the pedals more quickly.
Ten cylinders – the sports concept
Ten cylinders are the optimum concept for a high-performance sports en-gine: An engine of this kind has exactly the right dimensions, the right num-ber of components and filling capacities. And displacing 500 cubic centimeters, each cylinder is of exactly the right size, as defined by the really de-mand-ing engine specialist.
Compact construction for extra strength and enhanced comfort.
As one of the world’s leading engine manufacturers, BMW has become famous above all for its in-line power units. Now, focusing on the ten-cyl-inder, the engineers at BMW M GmbH have placed two rows of five cyl-in-ders next to each other at a V angle of 90° and with displacement between the two cylinder banks of 17 millimeters or 0.67´´, thus forming a very com-pact and dynamic configuration. The 90° angle was chosen for its vibration-and comfort-oriented mass balance, perfectly solving the conflict of interests between maximum smoothness free of vibrations and a high level of compo-nent strength.
The cylinder crankcase is cast in a low-pressure die-casting process using an over-eutectic aluminum-silicon alloy, in this case with a share of silicon of at least 17 per cent. The cylinder liners are formed by exposing the hard silicon crystals, with the iron-coated pistons running directly in the uncoated bore. Cylinder stroke measures 75.2 millimeters or 2.96´´, cylinder bore is 92.0 millimeters or 3.62´´, adding up to an overall capacity of 4,999 cc.
Like the engine blocks for Formula1, the M engine blocks are cast at BMW’s light-alloy foundry in Landshut just north of Munich.
Bedplate construction like in motorsport.
High engine speeds, high combustion pressure and temperatures subject
the crankcase to extremely tough and demanding conditions. The engineers at BMW Motorsport have therefore made the crankcase very compact and unusually stiff in a so-called bedplate structure, a technology carried over from motorsport. The BMW ten-cylinder is the first production V en-gine to feature such a bedplate construction.
The aluminum bedplate with grey-cast-iron inlays guarantees very precise crankshaft bearing – in particular, it keeps main bearing tolerance within close limits throughout the entire range of operating temperature. The grey-cast-iron inlays reduce thermal expansion of the aluminum housing and fea-ture special openings to provide a positive connection with the surrounding aluminum frame. At the same time this construction serves to fulfill the acoustic requirements made of the engine.
Specially designed for a high level of stiffness and finely balanced for
opti-mum precision, the crankshaft made of forged, high-strength steel runs in six bearings and weighs just 21.8 kg or 48.1lb. Designed for minimum mass inertia, the crankshaft offers a very high standard of torsional stiffness. In each case two connecting rods interact with one of the five crank journals displaced from one another at an angle of 72°. The small distance between cylinders of just 98 millimeters or 3.86´´ and the short crankshaft made pos-sible as a result interact with one another for a very high level of flexural and torsional stiffness on very low weight.
Lightweight engineering watching out for every gram.
The weight-optimized box-type pistons are cast out of a high temperature-resistant aluminum alloy and are iron-coated on the surface, weighing just 481.7 grams including their piston pins and rings. Compression height is 27.4 millimeters or 1.08´´, with a compression ratio of 12.0:1. The pistons are cooled by oil spray nozzles connected to the main oil duct. The trapezoidal connecting rods, in turn, measuring 140.7 millimeters or 5.54´´ in length, are weight-optimized, manufactured in cracked technology, and come in high-strength steel. This effectively reduces oscillating masses within the engine, each of the connecting rods forged from 70MnVS4 weighing just 623 grams including the bearing shell.
The single-piece aluminum cylinder heads on the V10 power unit are also cast by BMW at the light-alloy foundry in Landshut. As an important contribution to the appropriate temperature of the catalyst with the catalytic con-vert-er warming up quickly, the cylinder heads come with integrated air ducts for secondary air injection. A further feature is the typical configuration with four valves per cylinder characteristic of a BMW engine. The valves them-selves are operated by ball-shaped cup tappets with hydraulic valve play compensation. Tappet diameter is just 28 millimeters or 1.10´´, tappet weight 31 grams. The intake valves, in turn, measure 35 millimeters or 1.38´´ in diameter, the outlet valves 30.5 millimeters or 1.20´´.
Special innovations reducing the cost of maintenance
The intake valves are made exclusively for the V10. Measuring only
5.0 millimeters or 0.20´´ in diameter, they come with particularly thin shafts hardly im-pairing flow conditions in the intake duct. Valve clearance is automatically maintained at exactly the right point by hydraulic valve play compensation elements, helping to reduce the cost of ownership.
More power from the engine means a greater need for efficient cooling,
par-ticularly near the combustion chambers. With its crossflow cooling concept, the V10 power unit significantly reduces pressure losses in the cooling sys-tem compared with a conventional cooling configuration, guaranteeing a con-sistent distribution of temperatures in the cylinder head and reducing temperature peaks at all critical points.
Each cylinder is cooled consistently by an optimum amount of coolant flow-ing smoothly around the cylinders. To achieve this effect, the coolant flows from the crankcase via the outlet side of the engine through the cylinder head and over the collector rail on the intake side all the way to the thermo-stat and, respectively, the radiator itself.
High-pressure double-VANOS for an optimum cylinder charge
Variable double-VANOS camshaft management ensures an optimum charge cycle within the ten-cylinder. This, in turn, helps to keep valve timing ex-treme-ly short and fast – which in practice means more power, an even bet-ter torque curve, optimum responsiveness, greater fuel economy, and clean-er emissions.
Running at low loads and engine speeds, the engine therefore operates
with a greater valve overlap and, as a result, a higher level of internal exhaust gas recirculation. This, in turn, reduces charge cycle losses and improves fuel economy accordingly. As a function of the gas pedal position and en-gine speed – the parameters crucial to the power and performance required of the engine – valve increments are adjusted infinitely and by way of map control.
To ensure such efficient management, the sprocket connected with the crankshaft by a single chain is linked to the camshaft by a two-stage he-lical gearing. With the adjustment piston being moved along its axis, the he-lical gear pattern turns the camshaft relative to the sprocket, allowing vari-ation of the intake camshaft angle by up to 66° and the outlet camshaft angle by up to 37°.M double-VANOS requires a high level of oil pressure in order to adjust the camshaft at maximum speed and with maximum precision.
Accordingly, en-gine oil is compressed to an operating pressure of 80 bar by a radial piston pump fitted in the crankcase. This map-controlled high-pressure adjustment guarantees short adjustment times and provides the optimum spread angle synchronized to ignition timing and the amount of fuel injected as a function of engine load and speed at all operating points.
Reliable oil supply even in extremely fast bends.
The oil required for lubrication is delivered to the engine by a total of four oil pumps. The reasons for such an unusually elaborate and sophisticated oil supply system are the high standard of dynamic performance and the ex-treme acceleration of the BMW M6. In bends, for example, BMW’s large Coupe is easily able to achieve lateral acceleration of well over 1g. The cen-trifugal forces generated in such a process press the engine oil into the out-er row of cylinders to such an extent that the oil is no longer able to flow back in the usual process from the cylinder head, possibly leading to a lack of oil in the sump. And should worst really come to worst, the oil pump might then draw in air instead of oil.
To rule out such an eventuality, the engine comes with lateral force-controlled oil supply where, starting at lateral acceleration of approxi-mately 0.6 g, one of two electrically driven duocentric pumps draws oil out of the outer cylinder head in a bend and conveys it to the main oil sump. A lat-eral acceleration sensor serves as the actuator for initiating pump action. The oil pump itself is a volume-flow controlled pendulum slide cell pump deliver-ing exactly the amount of engine oil actually required by the engine. This is made possible by the inner rotor of the pump adjustable in its eccentricity versus the pump housing as a function of current oil pressure in the main oil duct.
A lubrication film which does not break when applying the brakes
When applying the brakes to the extreme, the BMW M6 builds up negative acceleration up to a staggering 1.3 g. Under such extreme conditions, it is quite possible that the flow of oil back to the oil sump serving as an intermediate storage reservoir will no longer be sufficient, especially as the oil sump for reasons of space is fitted beneath the front axle subframe. So if worst came to worst, lubrication might be entirely interrupted. To reliably prevent this eventuality, the engine of the BMW M6 comes with a so-called “quasi-dry sump system” incorporating two oil reservoirs: one in front of the front axle subframe, another behind the subframe.
A reflow pump integrated in the compressed oil pump housing draws oil out
of the small oil sump at the front and pumps it into the large oil sump at the back. Both the reflow openings and the compressed oil pump extraction point are precisely matched to the car’s acceleration and driving forces.
Ten individual throttle butterflies controlled electronically.
Again reflecting the supreme standard of motorsport, each of the ten cyl-inders comes with its own throttle butterfly, each row of cylinders being con-trolled by a separate adjuster. While this system is extremely demanding and sophisticated in mechanical terms, there is no better way to achieve engine response within split-seconds. To give the engine a particularly sensitive response at low engine speeds while building up power just as fast wherever necessary for dynamic performance of the highest standard, the throttle butterflies are masterminded electronically by two contact-free Hall potentiometers scanning and evaluating the position of the gas pedal 200 times a second.
Responding precisely to any change in running conditions, engine management sets the position of the ten individual throttle butterflies via the two ad-justers. Naturally, it goes without saying that all this takes place within frac-tions of a second. Only 120 milliseconds being required to open the throttle butterflies in full – roughly the time a driver takes to press down the gas pedal.
The benefit for the driver is instantaneous engine response with the car “taking off” without the slightest delay and the driver being able to sensitively dose the engine power required. At the same time electronic operation of the throttle butterflies makes the transition from overrun to part load and vice versa absolutely smooth and harmonious.
The V10 draws in the air it needs through ten flow-optimized intake funnels extending into two air collectors. The funnels and collectors are all made of a light composite material containing 30 per cent glass fiber.
Twin-chamber stainless-steel exhaust system.
As important as the intake side may be for giving the power unit of the M6 maximum output and performance, the exhaust system may not be neglect-ed in any respect. So here again, only the best meets the demanding stand-ards of the engineers and other specialists at BMW M.
The two five-in-one stainless-steel manifolds have been optimized in elaborate computer processes to provide exactly the same operating length.
To ensure exactly the right tube diameter, in turn, the stainless-steel pipes, produced as one unit without a seam in between, are formed from inside in an in-ternal high-pressure molding process and under a production pressure of up to 800 bar. And last but not least, the exhaust manifolds come with walls measuring only about 0.8 millimeters in thickness – again a clear sign of the utmost care and diligence the engineers at BMW M have given to each and every detail of this masterpiece in engine construction.
A high-performance sports engine clean and compatible with the en-vironment.
The exhaust system is designed consistently for minimum counterpressure, the dynamic gas flow is optimized for perfect power and torque. The exhaust system extends back to the silencers in two chambers, leading into the four striking tailpipes so typical of a BMW M Car. Compared to the M5, the sound of the exhaust on the M6 is even more muscular and aggressive.
As is to be expected of a BMW M Car, two trimetal-coated catalysts on each exhaust pipe clean emissions from the ten-cylinder in line with the demand-ing European EU4 and, respectively, the equally stringent US LEV2 stand-ards. Two catalysts are fitted in the underfloor, one catalyst each in the ex-haust pipe close to the engine. In conjunction with the thin-walled exhaust manifolds, these catalysts reach their optimum operating temperature as quickly as possible, a significant requirement particularly when starting the engine cold. Particular fortes of the system are its low pressure loss and high level of mechanical stiffness.
Engine control unit unique the world over
The MS S65 engine management unit is crucial to the outstanding
perform-ance and emission management of the V10. It ensures optimum coordina-tion of all engine functions, on the one hand, and the car’s control units, on the other. It also controls interaction with the SMG transmission.
This engine management system is quite unique in production engine technology worldwide: Incorporating more than 1,000 components, it has by far the highest level of package density. The hardware and software, as well as the specific functions of the system, have all been developed by BMW M.
High engine speed demands extreme performance
Given the high speed of the engine and the large number of management and control functions, the demands made of the engine management sys-tem are very significant indeed. To meet these demands, the MS S65 con-trol unit comes with no less than three 32-bit processors able to handle more than 200 million operations per second. Working with absolute pre-cision, they determine the optimum ignition timing from more than 50 in-coming signals individually for each cylinder and operating cycle, at the same time calculating the ideal cylinder charge, injection volume and in-jection point. The system also determines and sets the optimum cam-shaft spread, just as it adjusts the individual throttle butterflies.
Pressing the Power button, the driver is able activate a high-performance program calling up all of the engine’s power and performance. This program uses a more progressive map control line relating gas pedal to the opening
of the throttle butterflies and modifying the dynamic engine management func-tions for even greater responsiveness.
The more comfort-oriented of the two programs is called up automatically
as soon as the engine is started. The driver has the option to configure
the program switch-over function as a feature of the car’s MDrive control. MDrive also offers yet a further sports program for particularly dy-nam-ic motoring.
Engine management with a wide range of additional functions.
Electronic throttle butterfly control is based on a system of all-round output and torque management: The potentiometer on the gas pedal measures the driver’s demand for power and performance, translating this signal into the torque and output required at any given point in time. The output and torque manager then adjusts this power request by taking ancillaries and additional equipment such as the a/c compressor or alternator into account. Functions such as idle speed control, exhaust gas management and knock control are also coordinated and compared with the maximum and minimum forces re-quired for Dynamic Stability Control as well as Engine Drag Force Management. The desired power and torque calculated in this way is then set within the engine, focusing in the process on the current ignition angle. And last but not least, engine management performs a wide range of additional on-board diagnostic functions with diagnostic routines for the work-shop, additional operating functions, as well as the efficient manage-ment of peripheral units.
A new highlight in engine management: ionic current technology
Ionic current technology serving to detect any risk of the engine knocking as well as misfiring and miscombustion is a new feature of the en-gine control unit. “Knocking” is unwanted self-ignition of fuel in the cylinders. Engines without knock control have a somewhat lower compression ratio and a somewhat later ignition point, to make sure that none of the cylinders ever reaches or let alone exceeds the knock limit. However, this “safety” distance from the knocking limit means a trade-off in terms of fuel economy, engine output, and torque.
Active knock control, by contrast, allows the engine to run at its optimum
ig-nition point. Knock management protects the engine from damage
at all points where knocking is monitored and limited. The result, obviously,
is maximum efficiency on the road.
With conventional technology knock control receives its knock signal from various body sound sensors fitted on the outside of the cylinders. On a BMW M Car there is one sensor for each set of two cylinders. But as sophisticated and progressive as this technology may otherwise be, even this is not sufficient on a multi-cylinder, high-speed engine such as the new V10.
It is not able to reliably detect the risk of the engine knocking. And since at the same time a relatively high standard of monitoring accuracy is essential in the light of high engine speeds in order to guarantee appro-pri-ate combustion quality in the cylinders and, accordingly, a long service life of all components and appropriate emission control, the new technology now introduced is ionic current management.
Spark plugs with additional control functions
Using this technology, the engine is able, via the spark plug in each cylinder, not only to sense and control the risk of knocking, but also to monitor the ig-nition process and recognize any tendency of the engine to misfire. In other words, the spark plug serves both as a sensor observing the combustion pro--cess and as an actuator for the ignition. This marks the big difference versus a conventional knocking and ignition sensor fitted outside of the combustion chamber. Ionic current measurement, by contrast, is con-ducted directly within the combustion chamber, the spark plug itself serving as the sensor.
Measurements right in the middle of the combustion process
The temperatures generated in the combustion chambers of an internal
com-bustion engine may well be up to 2,500 °C or 4,500 °F. As a result
of these high temperatures and chemical reactions during the combustion process, the gasoline/air mixture in the combustion chambers is partially ionized. Particularly along the flame front, the gas becomes electrically conductive once ions are formed by the fission and accumulation of electrons (ionization). By means of the spark plug electrode electrically insulated from the cylinder head and connected to a control unit – the ionic current satellite – affiliated in turn to the engine management unit, the system is able to measure the ionic current flowing between the electrodes, with the spark plug electrode itself being kept under direct voltage. The level of such ionic current flow depends on the degree of gas ionization between the elec-trodes.
Ionic current measurement thus provides information on the combustion process directly where it counts, that is in the combustion chamber itself.
The ionic current satellite receives signals from the five spark plugs in each row of cylinders, amplifies these signals and conveys the data to the engine management unit. The control unit then analyses the data received and, where necessary, intervenes on specific cylinders, adjusting the ignition timing ideally to the combustion process by way of knock control.
This dual function of the spark plugs serving, first, as the spark-generating
unit and, second, as a sensor, helps additionally to facilitate diagnostic pro-cedures in maintenance and service.