The current Audi S5 coupe is gorgeous, fast, and luxurious, but at over 3800 pounds, it’s not dainty. And the upcoming 2010 S5 cabriolet will weigh about 4300 pounds—more than a lot of mid-size SUVs—so forgive us for thinking Audi product planners were being intentionally ironic when they spoke at the car’s launch about their green philosophy and success in downsizing. They conveniently neglected to mention weight and focused on their powertrain strategy: a far more efficient supercharged 3.0-liter V-6 replaces the naturally aspirated 4.2-liter V-8 in the S5 cabriolet and S4 sedan for 2010, with the S5 coupe getting the new engine for 2011. These cars are claimed to achieve the same acceleration as the V-8 models while using 20 percent less fuel.

Still, any idiot knows you can only get so far with engine downsizing in a performance car that weighs more than two tons. So we sat down with Michael ****, Audi's global head of product engineering, and asked him about how he squares the company’s stated smaller-is-better credo with the reality of its hefty cars.

Crash Dieting

We expected to hear some mumbo-jumbo about how safety standards and consumer expectations for features and refinement dictate ever-growing curb weights, but ****'s response shocked us: Audi is currently testing a prototype of the next-generation S5 that weighs 880 pounds less than the current car. He outlined the ongoing increase in the use of aluminum, magnesium, and high-strength steel as a main reason behind the mass reduction. The current TT's chassis is 69 percent aluminum, and the next-generation A6 (probably due in 2011 or 2012) will have an even higher proportion, **** says. The amount for the next A4/A5/S4/S5 will be higher still when they debut, likely as 2014 models.

**** also said that the supercharged 3.0-liter V-6 is an "intermediate step" for Audi. The next S4 and S5 will have lighter turbocharged four-cylinder engines. We can look at the TT lineup for direction: the base TT in the U.S. has a 2.0-liter turbo four that makes 200 hp. The TT S has the same basic engine, but makes 265 hp with beefed up internals and a bigger turbo. Future S4 and S5 models will have about 20 percent less weight and up to 30 percent less engine displacement than the current S5, making combined fuel economy in the mid to high 20-mpg range likely.

Good Looks, Lofty Goals

Although **** told us the existing S5 prototype uses the current car's styling, we were able to get insight into the next car’s design from another company source, namely the Sportback concept shown this year at the Detroit auto show. This "concept" isn't a concept at all—it's the Audi A7 that will debut later this year in production form. Company insiders tell us that while the car's overall proportions won't be used on other models, its sinister headlights, more-defined single-frame grille, and blade-like taillights will be defining graphic elements on the next generation of Audis.

So it will look good, and **** claims that even with all the safety and luxury features of today's car, it will weigh only 3000 pounds. He goes so far as to claim it laps Germany's famed Nürburgring Nordschleife eight seconds faster than the current S5. Skeptical? So are we. Industry sources tell us Audi hasn't yet taken enough weight out of the car's structure to achieve the stated goals, and we get the impression that **** is telling us about the project to force his development team to make good on the claims. If you assume a car's engineering must be completed three years before it goes into production, they only have a couple of years to achieve these aggressive targets. We wish them the best of luck.