The two cars' acceleration was a dead heat, but what of the difference in feel between supercharging and turbocharging? In this instance, there really was none. Both sixes masterfully integrate their respective boost systems, so throttle response is linear and you're never left waiting for a kick in the pants. With the engines' absence of supercharger whine and turbo whistle, and their tremendous flexibility across the rev range, an owner could drive either one of these cars for a year and never suspect that his engine was anything but normally aspirated.
The new S4 now offers a seven-speed S tronic dual-clutch automatic, while BMW continues with its six-speed automatic. But we wanted traditional six-speed stick shifts for our test cars to provide the purest sport-sedan driving experience. The 3-series' gearbox is a known quantity, with rather long throws but silky shift action and a beautifully weighted and calibrated clutch. It's no wonder the 3-series historically has enjoyed a higher take rate for its manual transmission than its competitors. The Audi offers shorter throws, but its shift action isn't as fluid as the BMW's.
Of course, the S4 has Audi's Quattro all-wheel drive as standard; BMW offers all-wheel drive as an option, but the 3-series is still a car whose identity is intrinsically wrapped up in its rear-wheel drive - the same way that Quattro is emblematic of Audi.
The most surprising discovery we made after repeatedly swapping back and forth between these two cars is how little the drive wheels mattered. For the longest time, the BMW's rear-wheel drive and its balanced chassis were seen as key components to its eager turn-in and throttle-adjustable cornering attitude. Audis, meanwhile, were nose-heavy, and their all-wheel drive, while great for taming slippery tarmac, did nothing to mitigate their terminal understeer.
For the 335i, that conventional wisdom pretty much still holds. We recorded a 51/49 percent front/rear weight distribution in the 335i, and as always, the sport-suspension-equipped BMW turned in with alacrity and felt neutral through the corners. But ever-wider tires, in staggered sizes no less, mean that the days of gently power-oversteering your 3-series through the esses are mostly just a memory.
The revelation was how similarly the S4 handled. We hammered down lumpy, narrow New York two-lanes with quick curves, sudden dips, and sharp crests. Through it all, the Audi reacted just as quickly, and it carved corners every bit as enthusiastically, as the 335i. We could even feel the push from the rear as we powered out of tight turns. Credit the combination of the slightly lighter front end (although the front wheels still carry 55 percent of the car's weight) and the Quattro all-wheel-drive system's 60 percent rear-biased torque split. Interestingly, our car did not have the S4's new torque-vectoring rear axle - which is included in the Drive Select package ($3950) or available as a stand-alone option ($1100) - but given what we experienced, its absence hardly seemed to be a handicap.