Bentley's 530-horsepower titanic convertible

Bentley showed off its Grand Convertible concept at the Los Angeles Auto Show, a massive open-top take on its Mulsanne model.

Wayne Cunningham Managing Editor / Roadshow
Wayne Cunningham reviews cars and writes about automotive technology for CNET's Roadshow. Prior to the automotive beat, he covered spyware, Web building technologies, and computer hardware. He began covering technology and the Web in 1994 as an editor of The Net magazine.
Wayne Cunningham
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Bentley Grand Convertible
Bentley's Grand Convertible concept shows off an upcoming new convertible model from the British automaker. Josh Miller/CNET

LOS ANGELES -- Taking a central position -- and a good deal of space -- in Bentley's exhibit area at the Los Angeles Auto Show sits a titanic convertible, bearing the appropriate name of Grand Convertible. Shown off here as a concept, the Grand Convertible shows that Bentley intends to produce an open-top version of its Mulsanne luxury sedan .

At the show, Bentley head of engineering Rolf Frech told me the company plans on keeping its line fresh, releasing new concepts or vehicles at every major auto show. However, given Bentley's limited model lineup, Frech says that the company uses a "derivative strategy," creating variations of existing models. Such is the case with the "Speed" versions of its Continental and Mulsanne vehicles, and so too the Grand Convertible.

In design, the Grand Convertible reminds me of the Rolls-Royce Drophead Coupe, as that vehicle was also launched with a two-tone hood, or bonnet in British parlance, and a wood tonneau cover. The Grand Convertible concept is painted in blue and has what Bentley calls a "liquid metal" hood. The prominent B hood ornament leads the car, with grille and headlight enclosures following the Mulsanne design.

Bentley debuts Grand Convertible concept in Los Angeles (pictures)

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As a convertible, the concept has only two doors, as opposed to the Mulsanne's four. This change dictates a number of challenges for the new car. Frech says that Bentley is still working on how to reinforce the body structure, in order to maintain the stiffness the Mulsanne gains from its hard top. That's one reason why the Grand Convertible is presently a concept.

When I asked Frech why Bentley chose a soft top rather than a retractable hard top, he responded that Bentley's strong ties to its heritage dictated the choice. Little is lost using a cloth top, however, as acoustic foam and other technologies let Frech engineer an appropriately quiet cabin for the concept.

Another area of heritage is Bentley's 6.75-liter V-8 engine. For the Grand Convertible concept, Bentley chose the engine out of the Mulsanne Speed, which uses twin turbos and direct injection to bring its total output to 530 horsepower and a staggering 811 pound-feet of torque.

However, Bentley's adherence to heritage goes only so far. When I ask whether Bentley would consider fitting an engine with a supercharger, a la the classic Bentley Blower, Frech replies that turbos are much more efficient, a large concern for Bentley in this era of CO2 and fuel-economy consciousness.