Installed in the Continental GT Speed, the latest W12 produces 626bhp and 607lb ft. Back in 2000, when Bentley inherited the Volkswagen Group’s 12-pot engine and set about re-engineering it, the unit produced 414bhp and 406lb ft.
The key figure is the maximum torque, which has been spread across a wider rev range and now comes in at 2000rpm, as opposed to the original unit’s peaky 3750-4500rpm range.
Read the full Bentley Continental GT Speed first drive
Of the latest revisions, which have come from engine management and turbo pressure alterations, Jones says: “This is the latest chapter in the W12 engine story, but not the last.”
Indeed, the future looks increasingly bright. Pyms Lane has been made the Volkswagen Group’s centre of excellence for 12-cylinder engines. That’s significant for several reasons: it means financial investment in the plant, creates about 100 new jobs, paves the way for increased production and means that Bentley will become an engine exporter for the first time.
So what drives Bentley’s passion for the W12 format? The engine – which is best described as two narrow-angle V6 engines sharing a common crankshaft – delivers the blend of refinement and power that suits the image it wants to portray.
“We’re always striving for these classic Bentley characteristics, which are maximum torque at low speed, almost like a locomotive,” says Jones. “A Bentley should be about huge, effortless acceleration. It shouldn’t feel like it is trying.”
The engine is more compact than a conventional V12 engine, which helps with weight distribution and packaging, key factors when Bentley was creating the brief for the original Continental.
“When we originally developed the Continental family of cars, it was envisaged as not being more than five metres long,” says Jones. “We wanted a four-seat car with good space for occupants and luggage. When you set those parameters, you start to establish the packaging envelope for the front of the car.
“Another criteria was that the car needed have lots of power to propel the occupants and their luggage with effortless speed, so it needed to be around 6.0 litres to get the kind of power we wanted.
"At the same time, it needed to have probably no more than 500cc per cylinder for emissions purposes, so that’s why a 12-cylinder worked. Given the packaging requirements, we said the best configuration would be a W engine, with its extremely compact layout.”
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Despite the engine’s complexity, the production line that it rolls off is comparatively straightforward. There are 10 work stations, focusing on crankshaft installation, piston installation, cylinder head installation, timing station, engine engraving, a leak test, loom installation and oil fill, a cold test and two phases of turbo installation.
This being Bentley, most of the processes rely more on human application than the robotic intervention that you might find in higher-volume production facilities.
The final phase is a full hot test cycle, which lasts for 21min 30sec. Unlike the earlier cold test, where the engine is turned using an electric motor attached to the flywheel, the hot test is a full petrol-powered fire-up in a sealed chamber.
“We carry out a hot test on every engine,” says Steve Ball, head of the technical department on the W12 line. “That is something that is unique to us. Most volume manufacturers will do the cold test, but when it comes to the hot test, most will only do about 10 per cent of their engines.”
Supplementing the checks and measures is a quality control process that’s overseen by head of quality Paul Willetts. His team works independently of the engine line, randomly selecting one engine out of every 100 for an eight-hour test, after which its power characteristics are checked against the manufacturer’s declared figures.
The news that Crewe has been made the Volkswagen Group’s centre of excellence for 12-cylinder engines has been met with pride on the factory floor, says Shaun McNeil, head of the engine shop. “The investment is recognition for the guys who work here and their levels of skill and knowledge. We think this engine is the heartbeat of the car.
"This is a driver’s car as well as a luxury car – a lot of our customers buy the Continental because they want to be behind the wheel, not sitting in the back – so the engine has to perform. You have sportiness, but refinement as well, and being able to provide a combination of both is an excellent piece of engineering.”
Life on the engine line is going to get busier as Bentley takes on more staff to deal with a production ramp-up from the current 3800 engines per year to approximately 9000 by 2017.
Bentley won’t be drawn on the specifics of its future product plan, but the W12 engine is set to power the British marque’s forthcoming SUV. Crewe is also taking over the supply of W12s for the Volkswagen Phaeton and Audi A8 from VW’s plant in Saltzgitter, Germany.
The toughest challenge facing the W12 will be meeting ever more stringent emissions regulations. The W12 engine isn’t able to adopt the cylinder deactivation used on its V8 sibling, which turns the engine into a V4 when it is under partial load to save fuel.
Read more about Bentley's new SUV
Jones says: “If you look at the complexity of the W12’s crankshaft geometry, to try to make cylinder deactivation work on that and keep the engine in balance is difficult. You might say why not shut down one bank of six cylinders, but the challenge of doing that is keeping the catalytic converter warm on that side.”
But ground has been gained. In the Continental GT Speed, the unit emits 328g/km of CO2, and the engine is compliant with phase one of the Euro 6 emissions regulations.
The adoption of a longer-legged eight-speed automatic gearbox in place of the old six-speeder has also contributed to emissions reductions. Looking forward, Bentley’s planned policy of hybridisation, which is due to reach fruition in 2017, could play a crucial role in enhancing the W12 engine’s prospects.
Jones remains bullish that Bentley’s engineers can keep the W12 engine relevant for years to come. He says: “We’ve brought the CO2 down and will continue to do so.
"The last time we had the engine anywhere close to this level of performance was with the Continental Supersports, which emitted 388g/km, so we’ve improved on that by 50g/km. As for the future, watch this space. We like challenges.”
Bentley's W12 engine in numbers
12.5 hours - the time taken to build a complete W12 engine at Crewe
2600 - the number of components in the W12 engine
90 seconds - how long the water pump, running at full capacoty, would take to fill a bath
70,000 units - the number of W12s produced at Crewe since the early 2000s
4000 litres - the amount of air that passes through the radiator every second at 206mph
900 degrees - the maximum exhaust temperature for the W12 engine
9000 units - Bentley's maximum W12 build capacity
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