F10 M5 from the inside

Knowing that the M5’s biturbo V8 and its ancillaries would add weight, the engineers at BMW M sought to reduce weight wherever they could in other areas. According to Helmut Gehring, head of suspension engineering: “Lower weight was the main objective when we redesigned the suspension for the new M5.”

If you look very closely at a front suspension strut, you will see the letters AlMgSiCu discretely stamped on its outer casing. Depending on various heat treatment regimes, this combination of Group 1 aluminum alloy comprised of aluminum, magnesium, silicon and copper is frequently used in the aircraft industry because of its low weight, high strength and good corrosion resistance.

The suspension arms and knuckles are made from forged aluminum, making them lighter and stronger than the standard 5 Series equivalents. With so much more power and torque going through the rear axle, the rear floorpan and subframe had to be beefed up. When the engineers were done, the uprated M5 suspension weighed around the same as a standard suspension, which is what they set out to achieve.

The kinematics and elastokinematics are unique to the car, whose ride height is about 20mm (0.8 inch) lower than a 535i. The 52/48 front/rear weight distribution is close to the 50/50 ideal, but the 0.33 drag coefficient is very average these days.

The new M5 has a lot of systems that add weight just by being there. The Dynamic Damper Control, the Brembo front brakes that use 15.7-inch vented discs with pin-decoupled alloy hubs and six-pot calipers, and the 9x19 and 10x19 alloy wheels and tires, all add up. When all is said and done, the new M5 tips the scales at just over 4,100 pounds.

The active limited-slip differential is similar in design to the M3’s, but is significantly strengthened to handle the M5’s power. It runs as an open diff when not under load, and has a locking range of 0 to 100 percent. Its casing is a combination of a cast-iron top housing, required to absorb the huge forces involved, and a cast-alloy lower housing with integral cooling fins. A gasket compensates for the differential expansion of the two metals used in this hefty 100-pound unit.

The M Differential uses sensors to detect yaw moment, yaw angle, throttle position, differential speeds between the two rear wheels and road speed. The information is fed to the controlling ECU, which compares inputs against its 3D maps, and sends back its response. All this happens within 10 milliseconds, so the car’s reaction to a given situation appears seamless to the driver.

As with the differential, the Getrag-built DCT dual-clutch transmission is similar in design to the M3’s DCT, but features considerably beefed up internals. This is no surprise as the M3’s naturally aspirated 4.0-liter V8 produces 414 hp at 8300 rpm and 295 lb-ft of torque at 3900 rpm, while the M5’s 4.4-liter twin-turbo V8 makes a whopping 560 hp at 6000 rpm and 501 lb-ft of torque from 1,500. With so much more torque on tap, the ratios in the M5’s seven-speed DCT gearbox have been made much taller. Where the M3’s Seventh gear is a direct 1:1 ratio, that job is left to Fifth gear in the M5, with Sixth and Seventh being over-driven for better highway fuel economy. Another factor is the slightly larger rolling radius of the M5’s tires compared to a stock 535i.

“The new gearbox has a 700Nm torque capacity,” Gehring explains. “It was a big challenge to strengthen the gearbox while trying to keep the weight roughly the same. It is, in effect, the M3 DCT unit with stronger components throughout.”

The engine is a variation on the 4,395cc TwinPower Turbo V8 first seen in the X5 M and X6 M, but with direct injection and Valvetronic variable valve timing. The new engine also has a revised intake system, bespoke exhaust and larger turbochargers with around 10 percent more flow capacity. “Our target was improved efficiency as well as better economy and emissions,” Jürgen Poggel, head of engine development, says.

“The airbox and intake trumpets are larger, and the diameter of the pipes that bring ram air from the airbox to the turbos were enlarged from 70 to 80mm.

“Valvetronic produces better response. The Double VANOS variable camshaft timing helps low-end torque, but Valvetronic improves cylinder filling and combustion, delivering a smoother transition from low to high engine speeds.

“In the past, you either had swirl or tumble in the combustion chamber, depending on valve lift,” he continues. “With Valvetronic, we can achieve both swirl and tumble at the same time, which gives us an efficiency gain of up to eight percent. In combination with Double VANOS, the gains are up to 12 percent.”

With less backpressure from the new exhaust, direct injection, Valvetronic and larger intercoolers, the M engineers were able to achieve the same power output with lower boost pressure. “We use just 1.9 bar compared to 2.0 bar on the 555-hp X5/6 M version of this engine,” says Jürgen.

The engine lubrication system is uprated, with a second oil pump in the front of the oil pan that sucks the life-giving fluid back to the sump when you are braking and cornering hard.

“Initially we considered a dry-sump system,” says Poggel, “but there is no room in the engine bay for a separate oil tank. In any case, we were able to meet our targets with this dual-pump system, which works under 1.3 g of braking and lateral acceleration on a racetrack.” –

2012 BMW M5

Layout
Longitudinal front engine, rear-wheel drive

Engine
4.4-liter V8, dohc, 32-valve, twin-turbocharged

Transmission
Seven-speed DCT dual-clutch auto-manual with console shifter and steering wheel- mounted paddles and Sport/Competition modes

Suspension
Independent multilink front and rear, coil springs, driver-adjustable variable dampers, self-adjusting, front and rear stabilizer bars

Brakes
Dual-circuit system, six-piston fixed calipers with ventilated steel rotors

Dimensions
Length/Width/Height (in.): 193.3/74.4/57.3
Wheelbase: 116.9 in.
Curb Weight: 4,123 lb

MSRP: $90,000 (est.)

Performance
Peak Power: 560 hp @ 6000 rpm
Peak Torque: 501 lb-ft @ 1500 rpm
0-60 mph: 4.1 sec.
Top Speed: 185 mph

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