GENEVA MOTOR SHOW: A 45 AMG is Merc's hottest hatch ever

Mercedes-Benz will be entering an entirely new world when it debuts the A 45 AMG at next month’s Geneva motor show.

Having given a select few outlets a ride in the A 45 a couple of months ago, AMG has finally announced the official details – and the numbers are every bit as impressive as development boss Tobias Moers promised.

Due in Australia around October this year priced at about $80,000, the A 45 AMG will be headlined by a 2.0-litre turbo-petrol four pumping out an incredible 133kW per litre to arrive at 265kW at 6000rpm.

It won’t just deliver power, either, with the under-square 1991cc four-pot (not 1.8-litre, as we were previously led to believe) delivering 450Nm at just 2250rpm and plateauing until 5000. It also still revs to 6700rpm and weighs 148kg fully dressed.

The result is a thumping 4.6-second sprint to 100km/h and it’s so enthusiastic at the top-end that it is reigned in by a speed-limiter at 250km/h.

"The A 45 AMG will enable Mercedes-AMG to appeal to new customers and tap new markets," AMG Chairman Ola Källenius said.

“We are adding an extremely attractive model with exceptional performance data to our range of unique high-performance automobiles."

And the A 45 won’t be the last of it, because it will also show the even-sportier CLA 45 AMG at the New York motor show in late March.

While the A 45 will be kept away from North America, the CLA 45 will be a truly global hotshot four-pot.

One senior executive from a rival German hotshop said it was one thing to push 181 horsepower per litre out of a racecar, but admitted AMG had moved the game on and provoked a specific-power war with the A 45 engine.

That admission was music to the ears of Mr Moers, who proudly insisted: "With the A 45 AMG we have well and truly achieved our aim of developing the most dynamic, powerful and efficient four-cylinder series production car.”

To do all this, the A 45’s twin-scroll turbocharger crams 1.8 bar of pressure into the engine, which is also fed via centrally located piezo injectors. These deliver multiple injections, backed up with multiple sparks, per ignition for clean burning and massive power.

It’s so clean that it posts an NEDC combined fuel economy figure of 6.9L/100km and emits only 161g/km of CO2.

AMG builds the engine on its own assembly line at Benz’s Kölledo plant in Germany. That means it’s built under the same roof as all of the A- and B-Class petrol engines, but it’s a lot more complicated than they are, even if it shares the bore and stroke dimensions of the base 2.0-litre.

Its block and crankcase are both sand cast and it scores tougher, lighter bits like forged pistons, a forged steel crankshaft and sodium-filled valves.

It attaches to a big-bore exhaust system, complete with a short-circuiting sports flap for more noise and energy, and finishes with a pair of chromed AMG exhaust tips.

There is also a huge front water-air intercooler with a supplementary cooler in the front wheel-arch, while the transmission cooler is built into the main radiator and has its own supplementary heat exchanger attached directly to the transmission.

While the default AMG response to any question or threat has always been to pile on more power, it knows that won’t work with a hot hatch. The attitude that has served it well with blacktop-bludgeoning V8s will need to be backed up with the balance and poise of the chassis package.

All this power was always going to overwhelm the A-Class’s front-drive chassis architecture, so AMG fitted the all-wheel drive A45 with a seven-speed dual-clutch transmission, complete with an in-built power take off to twist the rear axles.

The gearbox uses software adapted from the SLS’s seven-speed dual-clutch tranny (its shifts times in both Sport and Manual modes are just as fast as the SLS’s) and includes three software maps for different driving intensities.

It usually runs as a front-driver, but can send up to 50 percent of its performance to the rear axle in an instant. That’s because the rear diff contains a multi-disc clutch pack that’s fed by a two-piece prop shaft and the hydraulic pump controlling it is constantly driven.

Unlike other part-time all-wheel drive systems, that means the A 45 doesn’t have to wait for the computer to switch the rear diff’s hydraulic pump on.

The suspension, too, is barely recognisable as an A-Class item. It uses a three-link front-end with stiffer bearings, while a four-link rear-end scores stiffer bearings and new struts.

It all rides on 235/40 R18 rubber at all four corners, with 350mm x 32mm front brake discs and 330 x 22mm rears, though there is a 235/35 R19 wheel and tyre option.

It’s also much more focused inside, with aggressive AMG seats, steering wheel, pedals and switchgear supplementing the clean, modern A-Class interior package.