A word on Audi’s numbering system: A is for Audi. S is for Something more, and RS is for Really Something!
Well, that’s actually not what they mean, but it does provide something of a fix on where the Audi S6 and the new-for-2013 Audi S7 fit in the realm of Audidom.
With that as a guide, it’s obvious that the Audi S6 is an Audi A6 with more performance and handling, and the Audi S7 is an Audi A7 with ditto ditto. To further refine that, the Audi A6 and S6 are both four-door sedans while the Audi A7 and S7 are both what Audi calls a “five-door coupe.”
We’ll cut to the chase. The A7 and S7 hatchbacks, with a hatch that opens almost the whole of the car from the C-pillar back, giving it a utility a sedan could never have. With the rear seats folded, there’s more haul space, if not that of a wagon, but with the hatch closed, it’s a four-seat coupe/sedan with more panache than a wagon could ever aspire. With the rear seatbacks raised, there’s no passthrough to the cargo compartment, as there is with a wagon. If we’re allowed to nitpick, however, we’ll point out that the backs of the rear seats don’t fold to make a completely flat floor. Close but no tobacco product. (Click for our Audi A6 review).
But for as much as the Audi A6 and A7 differ aft of the B-pillar, the S models differ at least as much from the A models under the hood. There it’s a matter of cylinders and power. The A6 is powered by a turbocharged 2.0-liter four rated at 210 horsepower, new to the Audi A6 this year, or a turbo 3.0-liter V-6 making 301 horsepower. The V-6 is standard on the A7—or you can think of it as the four not being available in the A7, depending on your stance on whether the glass is half empty or half full.
Making the 6 or 7 an S, however, graces the engine compartment with a new twin-turbo V-8. The 4.0-liter direct injection engine is rated at 420 horsepower and just as important, spreads 406 lb-ft of torque across a plateau from 1,400 to 5,300 rpm. Audi pegs acceleration at 4.5 seconds from 0-to-60 mph and limits top speed electronically to 155 mph.
The twin-turbo V-8 replaces the naturally-aspirated V-10 from the last generation Audi A6, and as much as we liked saying “vee-ten,” the eight cylinder is an improvement not only in power but also in weight, with all the advantages that brings, from handling—reducing the forward weight bias—to fuel economy, with less weight to accelerate.
The new V-8 adds a fuel saving trick, deactivating four cylinders at light demand, allowing the engine to use fuel at the rate of a two-liter engine. Audi deactivates two cylinders on each bank. The end cylinders on the left side and middle two on the right, making the engine think it’s a V-4. A V-4, however, has a natural imbalance, but Audi handles that with a pair of “active” motor mounts that use built-in accelerometers and the crankshaft position sensor to activate electromagnetic coils in fluid to cancel the vibrations. Think of them as noise-cancelling speakers.
Because undesirable four cylinder sounds still sneak through, there are four microphones to pick up the sounds and then use the vehicle’s Bose or Bang & Olufson speakers to negate the unwanted sound. There is, we were told, no mother-in-law setting, but the system works whether the audio system itself is on or off.
Tech stuff follows: The cylinder deactivation system works by sliding the intake camshaft from the normal cam lobe to a zero-lift lobe. Fuel injection and ignition are halted and with the valves closed, the air in the cylinders acts like a spring, with little net loss in energy. Activation requires the engine be warmed to operating temperature, with revs between 960 and 3500 rpm in third gear of higher. After seven minutes of V-4 operation, regardless how balloon-footed the driver may be, the engine shifts back into V-8 mode to keep the idle cylinders from cooling off too much.