Like other automakers at the Detroit auto show, Bentley is speaking out of both sides of its mouth — in a good way.

At the 2009 North American International Auto Show in Detroit, the boutique British automaker unveiled its most powerful convertible ever and then pledged to reduce carbon emissions by at least 15 percent by 2012.

The new Continental GTC Speed convertible is the latest in the Bentley line of outlandishly fast cars. Like the Continental GT Speed that came out in 2007 and outsold the “regular” Continental GT by a 2-to-1 margin, the new GTC Speed puts out 600 horsepower from its 6-liter, 12-cylinder engine, 9 percent more than the standard GTC.

Torque is up 15 percent, for a total of 553 lb-ft, and Bentley says this is what really sets the GTC Speed apart. Full torque is available across a wide swath of the rev range, from 1,700 rpm to 5,600 rpm. In layman’s terms, this means the GTC Speed should easily deliver neck-snapping acceleration at any speed.

According to Bentley, it will sprint from zero to 60 mph in 4.5 seconds — 0.3 seconds quicker than the standard GTC. It will reach a top speed of 200 mph with the top up and 195 mph with the top down.

The automaker modified the self-leveling air suspension of the standard GTC to make the new GTC Speed more agile. The revisions include updated springs and dampers, new software mapping and lower ride height, 10 millimeters at the front and 15 millimeters at the rear.

Visual differences between the GTC Speed and regular GTC are subtle. On the exterior, front grilles are darker and the car has unique 20-inch wheels, wider exhaust outlets set in a black valance under the bumper, and a trunk-mounted spoiler for better aerodynamics.

Inside, there are subtle differences as well: a quilted diamond pattern in the leather on the seats and doors, a three-spoke leather steering wheel, drilled alloy foot pedals, and what Bentley calls a “knurled chrome and hide gear lever.” Those interior upgrades are based on a Mulliner Driving Specification package available on the standard Continental GTC for $9,070.

The Continental GTC Speed will go on sale in the summer of 2009 as a 2010 model. Wait time between order and delivery is expected to be between four and six months, which is the same for other models.

Bentley also announced plans to fast-track production of its first-ever alternative-fuel vehicle. It will debut at the Geneva Motor show in March and will be powered by a so-called “flex-fuel” engine that can run on gasoline or ethanol, a biofuel made from organic materials such as sugar cane or corn.

The company is focusing on biofuels such as ethanol as a way to reduce carbon emissions. To distance itself from the controversy over whether increased demand for ethanol is affecting food commodity prices, Bentley stressed that it is focusing on what Ulrich Eichhorn, Bentley board member in charge of engineering, called “second-generation” ethanol, which is made from nonfood plant fibers.

Bentley’s goal is to make all of its vehicles compatible with renewable fuels by 2012.