The horsepower war between European mid sized sedans continues as each manufacturer prepares its next generation entry. This is one war that shouldn't stop as it benefits all mankind. As we saw with the current E39 M5, later releases by Audi, Jaguar, and Mercedes, which employ forced induction, have pushed the once proud king down the podium of horsepower dominance.
Enter the E60 5 Series platform, which, regardless of what might be thought of the looks, is an awesome performer especially when mated to the 4.4L V8. The growl of the exhaust and overall response is reminiscent of the S62 B50 V8 found in the previous M5. To raise the standard, the E60 M5 will use a V10, designated as the S85 B50, which will be the first engine designed from scratched specifically for use in an M car. Why you ask, did BMW increase the number of cylinders and not simply the displacement? The answer can be summed up in BMW's vision of "Driving Performance". Simply put, this is the Bavarian's conceptualization of an overall optimization of performance, efficiency, economy, and safety.
M cars have always been founded on one governing design paradigm; create a distinctly different and awesome performance vehicle designed around a rear drive, naturally aspirated, manual transmission platform, based on an existing BMW chassis. M cars not only offer near track levels of handling and power, but also comfort and practicality for the street.
To achieve this in the E60 M5, M Division opted to use the same displacement but fitted into a 90* aluminum V10, which yields a more optimal per cylinder displacement and piston dimensions. A 90* design was chosen over a 72* V angle because of its more favorable vibration characteristics. This optimization of dimensions, and thus airflow qualities brings the maximum engine output to a total of 507 bhp, which breaks the 100 bhp per liter barrier. The new V10 only weight 2.2 pounds more than the old S62 B50. Too bad the muscle car designers of old were as efficient in this approach.
The V10 is designed around BMW's high revving concept. Instead of setting high torque as the goal and achieving that through supercharging, BMW engineers sought superior driving performance through high revs and a surplus of power at the rear wheels much like a racecar. The S85 borders on racing engine technology with its 12.0:1 compression ratio, unique engine management and continued power output at unconventionally high engine speeds. Structurally the S85 is the first BMW V engine to use a bedplate design. The bedplate is an aluminum structure with cast iron bearing inserts that replaces individual main caps to help distribute from the crank across the entire block. BMW even went to design unique self-centering main bolts that assure better stress distribution and obtain uniform bolt deformation.
Key to this increase of output is higher volumetric efficiency achieved through the use of ten individual throttle bodies driven by two e-throttle actuators, one per bank, and a bi-VANOS cam shaft phasing mechanism. The intake cam has a variable range of 33* of camshaft rotation and the exhaust cam has a variable range of 13.5* of camshaft rotation.
BMW's Valvetronic(R) system was not use on the S85 B50 engine. The current second generation Valvetronic system, which infinitely varies the intake valve timing by hydraulically altering fulcrum of the rocker guides, cannot operate reliably above 8000 rpm, just shy of the S85's 8250 rpm redline. Valvetronic's advantage is the reduction of engine response time by effectively eliminating the transient air charge in between the throttling element and the intake valve, which in this case are one and the same. As an alternative, the ten individual throttle bodies were mounted directly at the intake ports on the head. This keeps the transient charge volume to a minimum by eliminating the use of intake plenum(s).
The higher redline of the engine is also requires less valve-train mass, which for the S85 was reduced by 17.5%. Operating this is a new generation bi-VANOS system that uses higher hydraulic pressure, 80 bar (1160 psi) for faster actuation of the sliding gearbox that phase the camshafts.
All this performance meant that support systems had to be augmented also. M engineers developed a high efficiency cooling and oiling system, which consists of an isolated wet sump and four oil pumps: two electric, on mechanical drain, and one main variable mechanical pressure pump that delivers only the necessary oil required. The main pump was mechanical because of the Two electric pumps at the sides of the oil sump picks up oil from the outer cylinder head on each respective side and pumps it back into the sump once cornering loads exceed 0.6 g. Ultimately, the system can deliver the required lubrication flow at up to 54* of roll, or 1.3 g of lateral or breaking acceleration.To control all the systems of the S85 especially at its peak speeds, M engineers and Bosch developed the MS S65 control unit specifically for the M5. Equipped with three 32-bit processors, this unit capable of performing 200 million individual calculations per second. The MS S65 reads 14 digital and 44 analog signal inputs and outputs to 62 channels and 10 serial ports, which is comparable to the system used on their F1 engine. This is eight times the processing power of the E46 ECU of only four years ago.
After three years spent on research and development, BMW makes its first introduction of a combustion charge ion analysis system first to be implemented on the S85. Similar to Saab's system of the 90's and based on theories developed in the 30's, this ion analysis takes the place of a conventional knock sensor by monitoring the combustion event and combustions pressures for each cylinder. Using the spark plug as a positive pole and the cylinder as a ground, the ion current system measures the conductance of the air fuel charge throughout the combustion process. As combustion takes place and the charge chemistry changes, so does the electrical conductance of the contents of the cylinder. Based on the conductance as a function of crank angle, each individual combustion event is evaluated to better refine and control the sequential fuel and spark maps on a per cylinder basis. This is basically like a very smart version of an automotive oscilloscope. Unlike previous attempts of combustion ion charge analysis, the BMW system also discerns misfires either from inadequate fuel or spark, something neither Saab's system or a knock sensor can do.
To compliment the S85 V10, a seven-speed SMG only transmission was designed specifically for this car. This is the third generation version of BMW's SMG system, which is 20% faster than the previous generation. Shifts occur within 65 milliseconds. Much of this increase in response time is attributed not only to software changes, but the fact that this gearbox is mechanically only suitable for SMG use. To reduce shift throws and place high torque load gears near the transmission support bearings, the shift pattern of this Getrag box would be 2,4,6,7,5,3,R and 1st if looked at from a conventional manual shift pattern. 1st and second gears have triple fold carbon coated synchromesh while all higher gears have dual fold. To put it perspective how tight this gearbox is, sixth gear is a 1:1 drive ratio, and in 7th gear, cruising at 80 mph is keeps the engine at roughly 3000 rpm. Needless to say, seven gears are to many to manually shift for a streetcar, especially when mated to a twin disk Sachs clutch.This SMG Mk III is controlled by it independent transmission control unit (TCU) featuring a 16 bit 24 MHz processor. The Siemens TCU controls four electronic servo actuators that move in conjunction to alter the hydraulic circuit, which move the shift forks into the correct gear. Also controlled by the TCU is the hydraulic clutch cylinder for clutch engagement. Each system features its on set of hydraulic support systems, cooler, and sensor feedbacks.
It's hard to imagine all this technology working for you when you are behind the wheel of such a seamless mechanical marvel. Its one thing to say how great the car feels to drive, but that is only the tip of the M5 iceberg. For the geek in all of us, I hope this shopping list of gadgets in the M5 make you realize that it is worth every penny and makes you salivate all the more.
Bedplate and main block.
Custom main bolt
Spark plug and coil are integrated into an ion current measurement probe
Ion current measurement circuit
Each individual spark coil sits independently on the cam cover. The printed circuit board (PCB) at the front of the cam cover is where the ion analysis is performed. One sits on each bank.
Each individual spark coil sits independently on the cam cover. The printed circuit board
|Type||S85 B50||S62 B50|
|Displacement||4999 cc||4941 cc|
|Bore||92 m||94 mm|
|Stroke||75.2 mm||89 mm|
|Distance between cylinders||98 mm||98 mm|
|Line offset||17 mm||21 mm|
|Weight||240 kg||239 kg|
|Power||507 bhp @ 7750 rpm||400 bhp @ 6600 rpm|
|Specific power output||101.4 bhp/L||80.9 bhp/L|
|Torque||383.5 lbf-ft @ 6100 rpm||368.8 lbf-ft @ 3800 rpm|
|Maximum speed||8250 rpm||7000 rpm|