At the 2010 Detroit auto show, BMW introduced two variants of its 7-series, each intended to save fuel in its own way. The 740i uses a smaller engine than its sibling models, and the ActiveHybrid 7 complements its gas engine with an electric motor.
2011 BMW 740i
BMW takes a retro spin to the original launch of the 7-series by fitting it with an inline six-cylinder engine. Dubbed the 740i, this latest version of BMW's flagship sedan uses the same body and chassis as the previously launched 750i and 760i.
Recognizing the need for greener alternatives even at the luxury sedan level, BMW fits the 7-series with its twin-turbocharged 3-liter inline six-cylinder engine, similar to the engine used in the 135i, 335i, and 535i.
This engine uses two low-pressure turbochargers, each forcing air into a set of three cylinders, boosting horsepower up to 315. BMW says that's good enough to get the 740i to 60 mph in a respectable 5.8 seconds.
BMW's other green 7, a mild hybrid, complements its twin turbocharged 4.4-liter V-8 with an electric motor getting power from a lithium ion battery pack. This hybrid system allows start-stop capabilities, shutting off the engine when stopped in traffic. An eight-speed automatic transmission puts the power to the rear wheels.
BMW puts the total output of the gas engine and electric motor at 455 horsepower and 515 pound-feet of torque, big numbers that propel the ActiveHybrid 7 to 60 mph in 4.7 seconds, a time that BMW says makes it the fastest hybrid in the world.