First drive: Sledgehammer SLK55 AMG slinks in

MERCEDES-BENZ has introduced a blistering new AMG V8 to its latest-generation SLK roadster arsenal, backed up by a hefty $24,360 price cut.

The muscular new SLK55 AMG now costs $155,000, which is line ball with the C63 AMG Coupe, indicating a determination to shift more of the sportiest SLK.

As the fourth version of the third-generation SLK to arrive in Australia, it follows the four-cylinder SLK200 ($82,900) and SLK250 ($91,900), as well as the V6-powered SLK350 ($118,900).

Most significantly, however, it is the first model to debut Mercedes-AMG's new M152 V8 engine, which - unlike the twin-turbo V8 that powers other AMGs - is naturally aspirated.

Although the 5.5-litre V8 lacks the performance of the most potent AMG powerplant - and is much smaller than the German powerhouse's previous 6.2-litre V8, it still manages to generate 310kW and 540Nm.

This is up on the previous SLK55's older 5.4-litre V8, which made 265kW and 510Nm, and enables the new SLK55 to storm to 100km/h in just 4.6 seconds. Like most AMG and Mercedes-Benz models, this SLK is electronically limited to 250km/h.

Remarkably, AMG has managed to record an official fuel consumption rating of just 8.5 litres per 100km - about the same as a Camry - and CO2 emissions of 197 grams per kilometre.

Incredibly, the official fuel economy of the new SLK-AMG's 5.5-litre V8 is also just 0.2L/100km higher than the new SLK350, which is 2.0 litres smaller, has two fewer cylinders and makes 85kW less power.

Elements contributing to this figure include the lightweight nature of the engine, which tips the scales at only 187kg, as well as a series of fuel-saving measures including displacement-on-demand technology.

Mercedes says this system is ‘Formula One inspired’ although it is hardly new, with General Motors offering the technology since the 1980s and fitting it to the Holden Commodore's 6.0-litre V8, and Chrysler doing the same to its 5.7-litre V8.

With AMG's cylinder-deactivation system, cylinders two, three, five and eight shut down when the engine is not being worked hard. It can operate at any stage between 800rpm to 3600rpm when the engine is operating in relaxed Comfort mode, but switches off when the driver selects other more sporting modes.

AMG has also employed an idle-stop system to drive down the fuel economy figure by killing the engine when the vehicle comes to a halt. Similarly, this system comes on automatically in the standard C mode, but not in other modes and can also be manually switched off.

The company has retained its traditional seven-speed torque-convertor automatic transmission, which can be operated by steering wheel mounted paddles. There is no manual option.

AMG has fitted the car's exhaust with flaps that control the flow of gases for a more emotive sound when the throttle is opened wide.

The suspension is altered for a sportier set-up with stiffer dampers and spring rates combining with stiffer stabilisers and more pronounced negative camber on the rear axle.

An even firmer suspension tune is also available as part of the $8825 AMG Handling Package, which also includes a more aggressive rear differential for better drive out of corners, front composite brake discs and a three-spoke AMG Performance steering wheel.

The SLK55 features a Torque Vectoring Brake for the rear axle, a system that brakes an inside wheel for optimum cornering.

Like other SLKs, this one also runs the Direct Steer steering system, which reduces the degree of steering input required to change the direction of the vehicle at lower speeds, though this system has been tuned specially for the AMG model.

The AMG SLK shares the same bodywork as other SLK models, which have taken on a more masculine looked compared to the more rounded look of the previous model, which was deemed too soft by Mercedes designers.

But the obligatory AMG body kit and other more subtle exterior design upgrades enable it to be distinguished from lesser models.

Changes include a different front grille, lower bumper and larger air intakes, unique headlight surrounds, AMG daytime LED running lights and special tail-lights, along with quad exhausts with chrome outlet surrounds either side of a lower rear diffuser, which Mercedes admits is purely cosmetic at speeds allowed on Australian roads.

The top-shelf SLK sits on 18-inch rims wrapped with 235/40 tyres.

Standard features include Nappa leather-trimmed AMG sports seats with a solar-reflecting surface treatment, Harman Kardon Logic 7 sound system, satellite-navigation, 10GB music hard drive, Bluetooth audio streaming, internet browser with built-in Google maps integration and a race timing feature in the instrument cluster.

Mercedes-Benz SLK pricing (plus on-roads):
SLK200 BlueEfficiency (a)	$82,900
SLK250 BlueEfficiency (a)	$91,900
SLK350&nbsp BlueEfficiency (a)	$118,900
SLK55 AMG (a)	$155,000