Today's “supercars” don't make much sense, particularly if value for the dollar is a criteria.

That holds true for Audi AG's latest entry, the '07 RS4. The base price is $66,000. In real terms, it's probably not worth it. But in this rarefied class, the “sell” is not dollars and sense, but adrenalin and emotion.

By that measure, Audi's scorching new RS4 is a bargain.

BMW AG engineers, long famous for their own tinkering of the mighty M lineup of in-house “tuner” vehicles, would do well to start looking over their shoulders, because Audi is coming up fast.

The genre relies on silly horsepower above all, and in that respect, the '07 RS4 — the second generation of hyper-performance A4s from quattro GmbH, Audi's tuning and customization division — sets a new standard.

The RS4 uses a heavily modified variant of the Volkswagen Group's 4.2L DOHC V-8. But similarities end essentially with displacement, Audi is quick to point out: All the moving parts — including the FSI (Fuel Straight Injection) direct-injection fueling — are exclusive to the RS4.

It's one of the most bombastic V-8s in production. The power is sensational: 420 hp at 7,800 rpm; 100 hp per liter from a normally aspirated V-8 unarguably is exotic-engine territory. And the RS4's V-8 revs lithely to a thrilling 8,250-rpm redline.

You get one transmission only: the best 6-speed manual we've yet tried from Audi. The company's brilliant Direct Shift Gearbox automated manual is unavailable because of the V-8's longitudinal orientation and it's clutch-crunching potential.

The RS4 chassis offers a couple of sweet parlor tricks to complement the outstanding driveline.

First is a rear-axle bias for the signature quattro all-wheel drive system. Audi engineers have redesigned the Torsen center differential to bias torque, under normal traction conditions, 60% to the rear axle, rather than quattro's longstanding 50/50 torque apportionment. This has the effect, they say, of making the car handle more like a rear-driver, and it works. This is the most neutral-handling Audi we can recall.

The RS4 also is fitted with Audi's Dynamic Ride Control, a purely mechanical “adjustable” damping system that automatically stiffens each wheel's damper to counteract acceleration “squat” and brake “dive,” as well as body roll and pitch. The DRC system also makes a pronounced difference in squashing roll, but we think it could do a better job keeping the front end flat when one really steps into the RS4's seatbelt-stretching brakes.

Audi's sprayed around some satisfying materials in the RS4 interior, but apart from the exceptional Recaro sport seats, there's a bit too much of the conventional A4 still on display. Almost all of the minor switchgear and architecture is unchanged — a little off-putting when paying twice as much as the standard A4.

There are plenty of other serious performance cars available at the same price, or less, including the RS4's natural competitor, BMW's M3. The all-new M3 coming in 2007 also will, for the first time, flaunt V-8 power — and likely bring a commensurate leap in price to the RS4's realm.

But Audi beat BMW to the punch with a V-8 for its compact sport sedan (the S4 for some time has used a 340-hp, non-FSI variant of the 4.2L V-8), making the RS4 an ultra-performance car worthy of its heavy price. After all, 0-to-60 mph (97 km/h) runs of less than 5 seconds and a governed top speed of 155 mph (249 km/h) are not inconsequential.