Bentley's W12 engine tech secrets revealed

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.”

Read Autocar's history of Bentley

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.”