Most automakers use the additional energy provided by a hybrid system to get away with a smaller gasoline engine, thereby maintaining expected power but reducing fuel use. BMW looked at that extra power and thought, "Excellent, we can make our cars go even faster!"
Such is the case with the 2011 BMW ActiveHybrid 7, which hosts the same engine as the standard BMW 750i, a twin turbo direct-injection 4.4-liter V-8, but straps on an electric motor getting power from a 120-volt lithium ion battery pack. The result: substantially more horsepower and better fuel economy than the 750i.
Besides the power train, the ActiveHybrid 7 offers all the amenities of a typical 7-series. In fact, BMW makes many tech features standard on the hybrid that would be options on other 7-series models. Things such as the 16-speaker audio system upgrade, head-up display, and rearview camera come with the car, helping to justify its premium price tag, high even by BMW standards.
As the ActiveHybrid 7's hybrid system can't fully drive the car under electric power, it should be considered a mild hybrid system. Like Honda's Integrated Motor Assist system, BMW's hybrid system adds boost under acceleration and lets the engine shut down at stop lights. But the ActiveHybrid 7 feels much smoother.
From the driver's seat, there is little to indicate the hybrid system. As in other new BMWs, the tachometer has a blue region in the fuel economy gauge, indicating when the car is regenerating electricity from its momentum. The superwide 10.2-inch center LCD can be made to show a real-time animation of the car's hybrid power distribution, but its 3D presentation makes it more difficult to read than the power diagrams found in Toyota and Ford hybrids.
The clearest indication of the car's hybrid nature comes when it stops at a traffic light. The tach needle drops to zero as the engine goes silent. Take your foot off the brake, and the engine comes back to life with surprising smoothness, considering the size of the engine.
This idle stop system requires some getting used to, and is not preferable in some situations. It works great in places with particularly long traffic lights, as the car can sit there not burning gas or pumping out pollutants and carbon dioxide. But in traffic jams, with stop-and-go traffic, shutting down the engine for 5 seconds at a time is not as efficient, and is slightly annoying for the driver.
The amount of power on tap in the ActiveHybrid 7 also takes some getting used to, as the car lunges forward with just a light tap on the accelerator. Putting a hybrid label on a car may sound green, but the real virtue of this hybrid system is horsepower. The combined output from the turbo V-8 and the electric motor is rated at 455 horsepower and 515 pound-feet of torque. Compare that with the 400 horsepower and 450 pound-feet of torque in a 750i. The ActiveHybrid 7's power is closer to that of the V-12 760i.
BMW puts the ActiveHybrid 7's acceleration at 4.7 seconds to 60 mph, and it feels every bit that fast when you put pedal to metal, or pedal to plushly carpeted floor. The car surges forward, the traction control quickly adjusting power to keep tire motion useful, making for very little hesitation in the initial push. The big car feels steady and solid as it picks up speed, the speedometer slipping past 60 mph to hit 70, 80, and 90 in quick succession.
Although they use the same basic engine, the extra power the ActiveHybrid 7 has over the 750i doesn't all come from the hybrid system's electric motor. While figuring out how to make the gasoline and electric drive systems work in harmony, BMW engineers realized they could do away with things like the starter, the alternator, and the belt driving the air conditioning compressor. The hybrid system handles the tasks of those components.
Shedding that gear, and probably some clever tuning from BMW, increased the output of the 4.4-liter V-8 to 440 horsepower and 480 pound-feet of torque. The hybrid's electric motor, by itself, is rated at 20 horsepower and 155 pound-feet of torque. This motor sits between the engine and the transmission's torque converter. Its lithium ion battery pack forms an odd little cube in the trunk, a strange packaging decision on BMW's part.
But hybrid systems are supposed to have something to do with fuel economy, and so it goes with the ActiveHybrid 7, which gets EPA economy of 17 mpg city and 26 mpg highway, from 2 to 4 mpg better than the 750i. Driving over a combination of city streets, 65 mph freeways, and mountain highways in sport mode, the car turned in an average of 20.6 mpg. Nothing miraculous, but still quite good for a car of this power and luxury.
Given the hybrid system, you would think the car would suffer a handling penalty for carrying this extra gear, but it doesn't. Although 230 pounds heavier than the 750i, it holds the road well, its active suspension making sure that the tires stay in strong contact with the pavement.
A rocker switch on the console changes the damping through Comfort, Normal, and Sport settings. Comfort loosens up the suspension, making it smooth over bumps, while Sport screws it down tight. In this mode, the ActiveHybrid 7 corners very well, responding to steering input with precision.
However, all 7-series BMW models are big vehicles, and the optional active roll stabilization feature is smart technology to include. This feature puts rotary actuators on the front and rear sway bars that counteract the body's tendency to lean in corners. Lacking this feature, the weight of our tester ActiveHybrid 7 made itself felt in the turns. It is a worthwhile option, making the car much more capable.
The Sport setting also affects throttle response, making the engine's power more readily available. In addition to the rocker switch, the transmission has its own Sport setting, which makes downshifts more aggressive, and holds onto low gears longer. Keeping the tachometer well above 2,000rpm, the transmission's Sport mode defeats the gas-saving nature of the hybrid system.