Next 7-series will use all-new VB and six-speed auto.

MW’S NEW 7-series has an integrated powertrain that could serve as a blueprint for luxury cars over the next 10 years. Two all-new V8 engines have been coupled to an equally new automatic gearbox, the first in the world with six speeds.

The V8 engines have no throttles thanks to their revolutionary Valvetronic heads which control air intake by reducing valve lift. The first has a capacity of 3600cc and develops 238bhp at 5800rpm and 35.5kgm at 3800rpm. The second displaces 4398cc and produces 286bhp at 5400rpm and 45.3kgm torque at 3600rpm.

A nother first, a fully variable length induction tract, ensures torque is maximised throughout the rev range. Despite the high output, both engines meet tough EU4 emissions regulations.

BMW claims the engines are 14 percent more efficient than before. But that figure is not all attributable to the Valvetronic system, says V8 development chief, Johann Schupp. “About seven percent comes from Valvetronic,” he says, “three percent from reduced frictional losses and about four percent is due to the automatic gearbox.”

Like the 2.0-litre Valvetronic engine about to go on sale in the new BMW Compact, the engine has an open-deck block that directs coolant across the banks of cylinders rather than along them. The result is reduced drag and power consumption as well as more efficient cooling of the engine. Friction has been reduced in the heads by using chain drive, roller type actuators, lightweight valves and the lowest strength valve springs possible.

V

Induction tract revisions broden the torque curve of BMW's V8 engine.

8s are often thirsty but these two are fairly frugal, returning a combined consumption of around 9.24kpl. The secret lies in treating the powertrain as a whole to combine performance with efficiency. High-speed electronic networking and ‘mechatronic’ units in the gearbox ensure the two operate not as a double act, but as one.

The new ’box has a unique gearset produced by Lepelletier. Ratios are wider spread than a five-speed, optimising both acceleration and fuel consumption. The ’box is also 15mm shorter and 14kg lighter than a five-speed equivalent, and has a new type of torque converter which disconnects completely at idle, rather than ‘creeping’, to further reduce consumption.

More Valvetronic engines will follow even though a forthcoming in-line six for the 7-series is likely to be a carry-over unit from the existing 3.5. However, that doesn’t preclude the use of a new Valvetronic cylinder head, which could easily be designed to fit the existing block.