Bentley Continental Flying Spur
Published: 22nd February 2005
Bentley Continental Flying Spur
Bentley Continental Flying Spur - Powertrain
The heart of the Continental Flying Spur is its magnificent 6.0-litre, twin-turbocharged 12-cylinder engine which will propel the car to 60mph in 4.9 seconds and on to a top speed of 195mph. This awe-inspiring piece of engineering was created for both the coupé and four-door versions of the Continental and delivers phenomenal power (552bhp/411kW) as well as that legendary wave of torque (479lb ft/650Nm) from low revs that is the hallmark of every Bentley.
"When the decision was taken to produce the Continental family, we knew we would need an engine that was incredibly compact and well packaged to incorporate both its styling requirements and complex powertrain," reveals Dr Ulrich Eichhorn, member of the board, engineering. "From the outset the W12 concept was created with all the group's top products in mind. That is why we had significant input into the basic architecture of the engine. This basis was then developed extensively by Bentley to meet our exacting requirements - high torque at low revs and effortless acceleration."
Brian Gush, chassis, powertrain and motorsport director, explains the unique development process:
"The engine block is made from a hypereutectic aluminium alloy with silicon concentrates that reduce friction in the cylinder bores. Aluminium pistons were also specially developed to cope with the increase forces created by the turbochargers, which were themselves created exclusively for this Bentley engine."
The 12-cylinder block has a 48-valve head with four camshafts that operate using continually variable valve-timing. Power is transmitted via a seven-bearing crankshaft to the car's six-speed automatic transmission. To ensure that the large powerplant met stringent Euro IV and US LEV emissions regulations the twin turbochargers were designed with a unique bypass valve that automatically sends exhaust gases to heat the catalytic convertors when the car is started from cold. This valve then operates as the turbocharger wastegate at all other times.
The Borg-Warner turbochargers are also the ideal solution for producing the flat torque curve that is a key characteristic of every Bentley engine, ensuring that the driver has instantly available performance without a hint of turbo lag or having to shift down through the gears. That mighty torque curve is constant, with no drop-off from its maximum output of 479lb ft (650Nm) at just 1600rpm.
Packaging all those systems was a remarkable challenge in itself. The astonishing compactness of the engine - it is just 653mm long - was a critical target and with such immense amounts of torque it was equally imperative to have impressive traction in any conditions. What was called for was an all-wheel drive system that could cope with the Continental Flying Spur's performance capability and consequently as short an engine as possible to allow room for the extra componentry.
"The internal packaging of the engine is amazing," says Francis Ellison, module leader, powertrain. "And that helped when it came to designing all the other elements of the car's powertrain assembly. Because of the performance requirements, we wanted the centre of gravity to remain as low as possible and this meant we couldn't have the front differential under the engine. Instead we placed it between the engine and the gearbox. You can only do that if you have a very compact engine to begin with, otherwise you would have a car with a very long nose."
With ideal positioning of the main parts of the powertrain, the Continental Flying Spur has a 56:44 weight distribution over the front and rear axles. Unlike rear-wheel drive cars with large amounts of power, which are forced to put more weight over the rear wheels to improve traction, the Bentley's all-wheel drive system means the weight balance can be biased towards the front, thereby improving both the agility and handling of the car.
"Because we have a close to ideal distribution of weight, the Continental Flying Spur has excellent initial grip and turn-in when you start cornering," says Dr Ulrich Eichhorn. "You also get very good high-speed stability and it is much easier to tune an inherently stable chassis like ours to be agile than to make a nervous one stable."
Work was not just carried out on the performance capabilities of the engine but also its acoustic properties. The Continental Flying Spur has a re-engineered exhaust system that provides greater refinement for a car that has a broader role than the coupé.
"We have added a cross-tube in the centre of the exhaust system and we have also optimised the exhaust valve system to get the right acoustic pattern," explains Cameron Paterson, head of engineering for the Continental Flying Spur. "The exhaust note in the Continental GT coupé was deliberately quite noticeable - it is a sports car after all. For the Continental Flying Spur we wanted to ensure more refinement when you are driving in a leisurely fashion but still create that unmistakeable Bentley sound when you are pressing on. With this new exhaust system we can achieve that by closing off one tailpipe at differing engine load levels."
