Here's the bottom line: Audi has thrown just about every piece of new technology it has at the new S4, revealed here officially ahead of its public debut at next month's Paris motor show.
The upshot? A car that comprehensively outperforms its predecessor and leaves the German carmaker with one obvious problem: how to distance the upcoming RS4 enough to ensure that it still is regarded as the flagship of the A4 lineup when it arrives in 2010.
The big news first: The last S4's five-valve-per-cylinder 4.2-liter V8 is history. This model is powered by a brand-new supercharged four-valve-per-cylinder 3.0-liter V6 direct-injection gasoline unit, which also is earmarked for a facelifted version of the S5 due out next year. With 333 hp, the new 90-degree engine is down 11 hp on its well-received predecessor.
But before you go away and think Audi has caved in to those regulatory spoilsports who always seem to be demanding a curb on performance, consider this: With 325 lb-ft, the new unit also boasts a useful 23 lb-ft more torque. What's more, it's accessible from 2,500 rpm, some 1,000 rpm lower than before, and extends all the way to 4,850 rpm. The result? More usable performance at any given moment.
The new engine is a development of Audi's 3.2-liter V6, running the same 84.5-millimeter bore but a shorter stroke, 89.0 millimeters versus 92.8 millimeters. The compression ratio has been modified to better suit the move toward forced induction, dropping from 12.5:1 to 10.3:1. Sitting between the cylinder banks in the place usually taken by the inlet manifold is an Eaton Roots-style mechanical supercharger.
Audi's not giving away much more at the moment, but even with a gain in weight of 27 pounds over the existing naturally aspirated V6, the new engine--hailing from Audi's factory in Gyor, Hungary--is still lighter than the V8 it replaces. That means less mass up front. And because it sits in a newly engineered bay with the front differential positioned ahead of the clutch, as in all new Audi models using a longitudinal engine mounting, it is positioned six inches farther rearward than the old V8 in a move that improves overall front-to-rear weight distribution.
Channeling the engine's reserves to all four wheels is Audi's new rapid-shifting, seven-speed double-clutch gearbox and the latest version of its four-wheel-drive system, now featuring a nominal 40/60 apportioning of drive as well as a torque-vectoring planetary drive device at the rear. Referred to by Audi as an active-sport differential, it continuously varies the drive across the rear wheels to counter understeer and/or oversteer, taking less than 100 milliseconds to react, according to Audi.
The new driveline brings about a major improvement in standing-start acceleration; the S4's claimed 0-to-62-mph time drops from 5.9 seconds to just 5.1 seconds in sedan guise, a time that places it just 0.2 second behind the former 420-hp, 4.2-liter V8-powered RS4. Audi also puts 50-to-75-mph in-gear acceleration at 4.4 seconds, while top speed is limited to 155 mph. But it's not only at the strip where the differences between old and new are evident. A combined average of 24 mpg (U.S.) means a fuel-economy improvement of 7 mpg.
To cope with the added performance, the new S4 gains a retuned five-link (front) and trapezoidal-shaped multilink (rear) suspension featuring stiffer axle bearings, a three-quarter-inch reduction in ride height and standard 18-inch wheels shod with 245/40 profile rubber--developments, Ingolstadt insiders say, largely borrowed from the S5, which uses the same basic underpinnings.
Among a long list of options is Audi's drive-select system, which links the steering, variable dampers and differential to provide three states of tune: comfort, automatic and dynamic. In combination with Audi's MMI (multimedia interface), the driver can also preprogram a fourth individual state of tune into the system to call upon as desired.
Externally, things are a little different from the standard A4 sedan launched earlier this year. In keeping with the S4's performance brief, it gains a deeper front bumper, reworked headlamps, chunkier sills underneath the doors, aluminum-look exterior mirrors, a subtle trunk-deck spoiler and unique tail-lamp graphics. It's a subtle makeover, all in keeping with Audi's tradition of reserving the more muscular look for the more powerful RS4.
At this stage, there is no official word on the pricing of North American models, but our sources suggest the S4's added performance will come at roughly the same price as the outgoing model, so we figure it will start in the mid-$40,000s. It will go on sale in fall 2009.
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