It's easy to build a sports car: You make it lightweight and powerful with the engine, transmission, and occupants positioned towards the center of the car for better balance. Tune the suspension to serve up gluttonous portions of grip and balance and presto: You're done!

Performance sedans are another matter entirely, however. The engineers have to take a car that was packaged for comfort, convenience, and practicality and turn it into something special - something that makes the driver giggle on the right road at the right time, but that handles the daily grind as well as its mundane siblings. Currently, the BMW M5 sets the benchmark, although it's anything but perfect. The transmission, the looks and the universally loathed iDrive system all detract from the M5 experience, not to mention the fact it'll cost you close to $90,000 to put one in your driveway.

Enter the Audi RS4, Ingolstadt 's take on the uber-sedan concept, smaller and less complicated than the M5 with old-fashioned enhancements like mechanical differentials and a manual gearbox (that's a stick that pokes up between the seats that has to be moved around some to make the car go faster).

Although you might suspect its all-aluminum 4.2-liter V-8 is shared with the S4, other than the engine block it's basically an all-new motor. There are new pistons and connecting rods; a new crankshaft together with its bearings; new cylinder heads; a free-flow twin exhaust system and the latest direct-injection technology to help it achieve its stratospheric 8250-rpm redline. Power peaks at an astonishing 414 hp at 7800 rpm and maximum torque is 317 lb-ft at 6000 rpm, although 90 percent of its twisty impulse is available between 2250 rpm and 7600 rpm so there are no real flat spots anywhere in its delivery.

Power is channeled through a gloriously smooth and precise six-speed gearbox (there's no automatic or DSG option) and unsurprisingly, the RS4 is rather zippy: 0-62 mph takes just 4.8 seconds, 0-125 takes 16.6 seconds, and top speed has to be capped at 155 mph.

Four-wheel friend

The RS4's quattro 4WD system is also heavily modified. The center Torsen differential is now biased 60:40 in favor of the rear wheels, although 100 percent of the engine's available torque can be sent to either axle at any time as needed. There's a hypoid gear differential on both axles to distribute torque to the wheels and the whole system is backed up with a two-stage stability control system that even wipes the brakes rotors for you in the wet.

The suspension system uses the A4's basic front four-link and rear double wishbone arrangement but a brilliantly simple active ride system has been added that doesn't use any electronic devices. Each damper is hydraulically linked to its diagonally opposite counterpart and the movement of fluid, which is controlled by a central valve, helps to stiffen of soften the shock absorbers to counteract roll, dive and pitch while maintaining a compliant ride while cruising. The steering has been retuned for sportier driving also and the brakes are now enormous ventilated and cross-drilled rotors that measure 14.4 inches at the front and 12.8 at the rear. The front brakes also boast eight-piston high-performance calipers with four brake pads, while the rear brakes use single piston stoppers.

As you might expect, pedal feel and brake performance is exceptional, shrugging off the RS4's considerable 3957 pounds of heft on some of California's most challenging roads with no loss of performance or signs of fade. The whole performance package is topped off with glorious 19-inch wheels wrapped in sticky 235/55 Pirelli P Zero rubber, peaking out from underneath bespoke fenders that are extra flared to cope with the RS4's wider track, which grows by 1.5 inches at the front and 1.8 inches at the rear. The front fenders, along with the hood, are made of aluminum to help the RS4's weight distribution (58 percent of which still sits on the front axle) and elsewhere, new bumpers, side skirts, and a new trunk lid with an integrated spoiler complete the RS4's muscular makeover.

All clad in leather

Inside, potential buyers will be sorry to hear that the two-piece racing buckets and flat-bottomed steering wheel fitted to the European models aren't available on U.S. models, as they're too expensive to make compliant with safety regulations. To be honest, making do with the Recaro front seats and leather-clad steering wheel from the S4 isn't exactly what I'd call slumming it, as both are exceptionally comfortable and sufficiently grippy even for track use. Besides, I was so engrossed in the driving experience I could have been sitting on broken glass and I wouldn't have cared.

As a driving tool, the RS4 is simply staggering, offering the intimate feel and razor sharp responses lacking in the rather serious S4 sedan. Turn-in is phenomenal, with every minute steering input causing an immediate change in the RS4's trajectory and because there's almost no roll from the car's trick suspension, cornering forces are simply ferocious. The steering is perfectly weighted and full of communication but it's also a very refined set up that is completely devoid of kickback and artificiality. Whereas the S4 reminds you every second that there's a massive V-8 hanging out over the front axle the RS4 feels perfectly balanced and poised, communicating and playing along with you by letting you know exactly what each wheel is up to. That's not to say it's not bombarding you with every piddly little detail of the road surface beneath - it gives you just enough info to make it fun and filters the rest out so as not to wear you out. That not only makes the RS4 a reasonably comfortable cruiser, it's also very, very easy to drive hard for long periods of time.

I'm utterly and completely smitten by the RS4. Not only is the best looking supersedan on the market, it's also one of the fastest and most faithful point-to-point cars in the world. The driving experience is simply phenomenal, the V-8's cultured howl is simply addictive and yet it's as comfortable and well equipped as you could want, without resorting to the technological overkill that plagues the M5. To me, the Audi RS4 is like an Evo in Armani: Intimate, pure, fast and fun, but oozing style and class as well.

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