Next Benz SLK AMG won’t be force-fed

MERCEDES-BENZ has confirmed the flagship of its third-generation SLK roadster range will be powered by a naturally aspirated version of the twin-turbocharged 5.5-litre V8 that will do duty in other AMG models.

Hence, the top-shelf compact convertible, which will make its global debut at the Frankfurt motor show in September before arriving in Australian dealerships in the first quarter of next year, will continue to be known as the SLK55 AMG, rather than falling into line with all other AMGs by adopting a’63’ badge.

Bearing no relationship to the naturally aspirated 5.5-litre V8 that powers Mercedes’ E500, S500 and ML500 models, the new M152-codenamed engine of the same capacity adopts a new variable-displacement system developed by Mercedes-AMG.

According to Mercedes, the combination of direct petrol injection and AMG cylinder management allows the 2012 SLK55 to deliver the fuel consumption of a four-cylinder while remaining the only V8-powered roadster in its segment.

The non-turbo 5.5-litre V8, which revs to 7200rpm, produces 310kW at 6800rpm and 540Nm of torque from 4500rpm, making it 45kW more powerful and 30Nm more muscular than the 265kW/510Nm supercharged 5.4-litre V8 it replaces in the previous SLK55 AMG.



At the same time, the twin-turbo V8’s standard idle-stop system and an alternator that only engages during engine overrun or braking combine with the new AMG cylinder management system helps reduce fuel consumption by 3.5 litres per 100km, to just 8.5L/100km (NEDC provisional). CO2 emissions are also reduced by about 30 per cent, to just 199 grams per kilometre.

AMG says its new cylinder shut-down system – similar to the Chrysler 5.7-litre HEMI V8’s Multi-Displacement System and the Active Fuel Management technology employed by Holden’s 6.0-litre Commodore V8 – disables two or four cylinders to save fuel in low-load situations at engine speeds between 800rpm and 3600rpm, and can switch from four-cylinder to eight-cylinder mode in just 30 milliseconds.

It also claims the new all-aluminium V8 – which features 12.6:1 compression, aluminium pistons, carbon-coated piston rings, cast-in Silitec cylinder liners, fully variable valve timing and a variable exhaust system that gradually opens internal baffles above 2000rpm to produce a louder and sportier exhaust note much like HSV’s bi-modal exhaust system – still offers 230Nm of torque in four-cylinder mode.

The new 5.461-litre M152 V8 comes with the same oversquare (98.0 x 90.5mm bore x stroke) cylinder dimensions as the biturbo M157 V8 that debuted last year in the CL63 AMG as the first evidence of Mercedes’ ‘AMG Performance 2015’ strategy, but weighs slightly less at 187kg dry.

New features include revised intake air ducting, new cylinder heads, a modified valve drive, adapted oil supply system and an optimised crankcase.

Naturally, however, shedding the twin-turbo set-up of the M157 – which powers the CL63, CLS63 and S63 AMGs in Australia and will be seen here in the facelifted C63 AMG sedan and wagon (but not the C63 AMG coupe) in September, and the upgraded E63 sedan in November – also reduces performance.

In other AMG models the biturbo M157 replaces the M156 6.2-litre naturally aspirated V8 and produces between 386kW/700Nm and 420kW/900Nm with an optional Performance Package – some 110kW and some 360Nm more than the 2012 SLK55 AMG’s non-turbo engine.

Mercedes-AMG says it produced more than 68,000 M156 V8s since 2005 – setting a new record for AMG, which dates back to 1967 – with the 6.2-litre engine developing as much as 386kW and 630Nm.

In the upcoming C63 AMG Coupe, it delivers 358kW in Performance form, while AMG’s 6.2-litre V8 also continues in dry-sump M159 guise in the 420kW/650Nm SLS AMG super-coupe, the roadster derivative of which goes on sale next year.

Debuting in 2001, the previous SLK55’s blown V8 was another milestone in the history of AMG, which dates back to 1967. Codenamed M113 K, it developed up to 428kW and 800Nm, while the SLR McLaren’s M155 version appeared in 2003 with outputs of 478kW and 820Nm.

While AMG’s 6.0-litre biturbo V12 engine also continues in the top-end S65, SL65 and CL65 AMGs, it’s understood the twin-turbo M157 V8 could not be packaged in the sleek new SLK, which made its Australian debut at this month’s Melbourne motor show before garden-variety four-cylinder and six-cylinder versions arrive here in August with a $10,000 starting price cut to $82,900.

Mercedes this week released a blurry image of the new SLK55 AMG, which shows it will feature the expected additions of an AMG body kit with aggressive black air inlets, plus black bonnet and fender vents and unique black AMG wheels.

Expect the new SLK55 to also receive the traditional AMG suspension tweaks and the AMG Speedshift MCT version of Mercedes’ seven-speed automatic transmission, which replaces a torque converter with a wet start-off clutch.

“Top performer for fuel economy and maximum output: with the new 310kW AMG 5.5-litre V8 engine we have once again created a real masterpiece,” said Mercedes-AMG chairman Ola Källenius.

“The M152 sets an outstanding example for efficiency, while demonstrating the creativity and expertise of our engineers, who took their inspiration from Formula 1 when developing the cylinder shut-off system.

“This makes the new, naturally aspirated eight-cylinder the perfect power unit for the new SLK55 AMG, which will celebrate its premiere at the international motor show in Frankfurt in the autumn.

“Thanks to the innovative AMG cylinder management system and other high-tech components, our newly developed AMG M152 naturally aspirated eight-cylinder engine achieves the fuel economy of a four-cylinder with the muscular power delivery and emotional sound experience of a V8.

“A sportscar engine with technology taken from Formula 1 – I am convinced that the new SLK55 AMG will meet the high expectations of all sportscar fans.” Mercedes says the M152 underwent 8000 hours of endurance testing alongside its twin-turbo M157 sibling, with painstaking attention paid to the cylinder shut-off, idle-stop and exhaust flap systems in “every climatic zone on earth”, including “the icy cold of northern Sweden, the merciless heat of Death Valley (USA), lapping the high-speed circuits in Nardo (Italy) and Papenburg or in stop-and-go traffic”.

In tandem with the SLK55 AMG engine reveal, Mercedes also announced 2001 F1 runner-up David Coulthard as an AMG brand ambassador. The 40-year-old Scot and Mercedes-Benz DTM touring car driver will also be part of the upgraded E63 AMG’s marketing campaign.

Mercedes-AMG also announced the opening of a new 525 square-metre ‘Private Lounge’ at its Affalterbach headquarters in Germany, for the use of more than 15,000 worldwide members of the AMG Private Lounge Community.

“The new AMG Private Lounge in Affalterbach is an exclusively and unusually designed meeting-point in which to spend time,” said Mr Källenius.

“We see it as a second living-room for our customers. We want the AMG Private Lounge in Affalterbach to provide the perfect setting for the most exciting day of the year – for example when our customers take possession of their new AMG-Mercedes here in Affalterbach.”