A wry smile sneaks across Tobias Moers’s face as he fires up the engine on a Mercedes A45 AMG prototype at the Hockenheimring in Baden-Württemberg, Germany. “This car doesn’t exist,” the head of development at Mercedes-AMG explains, “and that’s why you cannot drive it!” As Moers jumps behind the wheel and I settle into the perfectly sculpted passenger seat, there’s no doubt that this is a real car, albeit not one that’s available yet in dealerships.

We ease out of the pit lane and onto the track. At this point, the car sounds like most of its four-cylinder Mercedes siblings—emitting a rather undistinguished, but not unpleasant, moggy purr. But as Moers dips deeper into the throttle and the 2.0-liter engine revs higher on the approach to the first right turn, the sound segues into a powerful rort. The car has come alive. It storms out of the turn, pulling strongly and without any of the torque steer you’d expect if this were a powerful front-drive car, but AMG wisely chose an AWD configuration for the A45. Body control is excellent; roll, pitch, and dive are virtually nonexistent as the AMG prototype charges around the track. The balance and the lack of torque steer are certainly helped by the fact that the A45 prototype shuttles its prodigious power to all four wheels, one of several forthcoming AMG products that will do so. On this car, the power distribution between the two axles is handled by an electronically activated multiplate clutch. Sending an estimated 353 hp and 332 lb-ft of torque to just the front axle would have been, uh, unwise.

To squeeze this much power out of a 2.0-liter four-cylinder, AMG equips it with a high-pressure turbocharger pumping a race-car-like 26 psi of boost. Special bearings and solid pistons handle high internal pressures akin to those found in a diesel engine. Moers claims this souped-up 2.0-liter is as durable as any other AMG engine, undergoing the same rigorous testing regimen as any other Mercedes product. The A45 we’re in hits more than 124 mph at Hockenheim without any apparent stress.

The A45 AMG is the most powerful series production car powered by a 2.0-liter engine. Its specific power output is roughly 173 hp per liter, topping even the Porsche 911 GT2 RS (172.2 hp per liter). That’s a record for roadgoing cars, according to Moers.

Like the SLS AMG, a seven-speed AMG Speedshift MCT dual-clutch gearbox is used to handle the enormous power and torque of the A45 AMG engine. (We’re fairly sure they are different part numbers.) As is current AMG fashion, the A45 comes with the so-called AMG Drive Unit that enables the selection of different driving modes. In Normal mode, gearchanges are smooth and seamless; selecting Sport or Sport Plus mode noticeably quickens the swaps. In Sport Plus, it delivers competition-grade downshifts and simultaneously performs matched-rev throttle blips to keep the car composed during serious driving. Aside from the stability benefits, the blip-throttle sounds are entertaining. And for spectacular NHRA-like full acceleration from a stop, the A45 AMG is equipped with launch control.

Back at the Hockenheim track, Moers is tossing the compact Mercedes A45 AMG through tight corners, demonstrating its sharp steering, crisp throttle response, and neutral balance even at very high cornering speeds. Hard braking, turning the car into the corner, and downshifting all at the same time do nothing to upset the car—or Moers’s smile, for that matter. The A45 is the smallest car ever tuned to an AMG fare-thee-well.

Is there a market for another compact monster like this? Mercedes thinks so and is targeting customers who are currently driving an Audi RS3 or a BMW 1-series M. The way the company’s marketing people see it, this fresh-looking performance car with Mercedes styling and design details could be a winner. In Germany, the equivalent of $64,000 is a lot of money for a Mercedes A-class, but we see it as fair for a compact car that delivers Porsche-like dynamics.

We’ll find out if M-B’s gamble pays off next August when the A45, the most powerful A-class ever, hits European markets. U.S. customers, however, won’t get the chance to buy one. But don’t fret: Mercedes will offer this same high-performance AWD 2.0-liter turbo package to American buyers for about $50,000 via the new CLA45 AMG, a swoopy new sedan that debuts a few months later. We can’t wait.

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