Within the thems big words department, Audi is calling its A8 Hybrid the efficiency customary. And its not specifically untrue since the top-of-the-peak, 211-horsepower 2. 0-liter sedan boosted by a 45-hp electric motor has a lot of power than an a3 tdi but a faster 0-60 sprint, nevertheless the gas mileage comparison isnt unfavorable : the a3 gets 34 miles per gallon combined, the A8 Hybrid does 38 mpg. And you get all that A8 size and panache. And 21-inch rims. Responsibly.
The basis for the A8 hybrid is the Volkswagen Group’s 2.0-liter turbocharged inline-four. Sporting direct injection and variable valve timing and lift, output is the same as in the A4: 211 hp and 258 lb-ft of torque. Connected to the crankshaft via a wet-plate clutch is an electric motor that puts out 44 hp and 156 lb-ft. Another clutch is slotted between the electric motor and the eight-speed automatic gearbox. Power is routed to the front wheels only, and total system output is quoted as 241 hp and 354 lb-ft.
The operation of the hybrid system is pretty straightforward. The electric motor assists at speeds up to about 40 mph and the car can also travel just over a mile in full-electric mode. A power meter in place of the tachometer on the instrument panel displays how much electric assist and charge is provided by the electric motor. The motor can also act as a generator to recapture energy during braking; the stored energy resides in the A8 hybrid’s compact lithium-ion battery pack, which sacrifices four cubic feet of trunk space, with 14 remaining. The battery also powers an electric A/C compressor and the electric power-steering system.
There are other hybrid penalties besides the modest loss of trunk space, not counting the indignity of driving a front-drive, four-cylinder A8. A bloated curb weight is one of them. Unfortunately, we can’t say how much, because Audi hasn’t released weight figures for the standard A8. And while the A8 hybrid does have half the cylinders of the 4.2-liter V-8 we’ll see in U.S.-bound cars, its inline-four is heavy with an iron block plus a turbocharger and an intercooler. If you add in the electric motors and battery pack, it’s difficult to see how the A8 hybrid will be an ounce lighter than our 4400-pound estimate for the A8 4.2. Despite this evidence, Audi says the A8 hybrid weights 4186 pounds.
Whatever the weight may be, Audi estimates the A8 hybrid will go from 0 to 62 mph in 7.6 seconds. If that figure is conservative (as is typical of manufacturer claims), then the A8 hybrid should be about as quick as the Mercedes-Benz S400 hybrid we tested, which does the 0-to-60 sprint in 7.1 seconds. That’s not bad for a car that uses 20 percent less fuel than a conventional A8 on the European urban cycle. Fuel economy on the combined European cycle is a claimed 38 mpg.
So why won’t Audi bring the hybridized A8 here, especially when Mercedes-Benz offers the S400 hybrid? Cost and volume are the main answers. Audi sells the A8 here in relatively low volumes, especially compared to the S-class. With hybrids composing a small slice of the model mix, it just doesn’t make financial sense to bring the hybrid model stateside. Instead, we’re likely to see this hybrid powertrain show up in a Q5 wrapper sometime soon, while Audi continues to pin its U.S. green credentials on clean diesels (possibly including the A8 TDI) followed by the all-electric e-tron sports car in 2012. Key hashtags: #audi, #hybrid, #concept.