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AMG keeps it real with new SLK55

2011-08-22 08:27

BEST GETS BETTER: More powerful, more efficient and acoustically impeccable thanks to 2 000rpm activated exhaust flaps, AMG new (naturally-aspirated) V8 is the business.

Vehicle Specs
Manufacturer Mercedes-Benz
Model SLK55 AMG
Engine 5.5l V8
Power 310kW @ 6 800rpm
Torque 540Nm @ 4 500rpm
Transmission Seven-speed auto
Zero To Hundred 4.6 sec
Fuel Consumption 8.4l/100km
When Mercedes-Benz revealed its third-generation SLK in January of 2011 a new SLK55 was expected in due course.

The bothersome question, though, was whether AMG’s seminal compact hot roadster would retain its fabled naturally aspirated V8 or switch to turbocharging – as nearly all AMG’s products are expected to do by 2014.

Well, the good news is that the new SLK55 AMG, due to be revealed at the 2011 Frankfurt auto show in September, has retained its 5.5-litre non-turbo V8.

Considering the S-Class, E-Class and CL-Class AMG models have already converted to Affalterbach’s new twin-turbo, 5.5 V8 (internal codename M157), having Mercedes-Benz’s official media release confirm the new SLK55’s naturally aspirated V8 engine configuration will undoubtedly thrill followers of the badge.


As the only compact German V8 roadster available, the SLK55 has generated a loyal following and those owners keen to upgrade (yet fearful of the addition of turbos) will be delighted by the new car’s specifications.

The new SLK55’s V8 is essentially an M157 spec engine sans its two turbochargers - a crucial design change as the SLK’s engine bay architecture would (allegedly) not be able to accommodate the 5.5 V8 with its associated turbochargers and elaborate exhaust.

With the pressurised plumbing removed, a new cylinder head and intake manifold have been bolted into place, with mechanical drag reduced by a slicker oil system and redesigned crankcase.

Statistically the un-blown M157 engine (internal code M152) is good for 310kW (at 6800rpm) and 540Nm (at 4500rpm), bettering the current SLK55’s 265kW and 510Nm. Beyond the notable increase in power output (45kW), new SLK55 claims to emit 30% less emissions and is (plenty) lighter on fuel thanks to start/stop technology and the ability to run on only four cylinders when peak performance is not required.

In four-cylinder mode the SLK55’s engine is still capable of producing 230Nm of torque to ensure sufficient acceleration in combination with low consumption. As engine speed passes 3600rpm the SLK55 switches from four to eight-cylinder combustion within 30 milliseconds as the engine control module recognizes the greater demand for performance.

Mercedes-Benz claims the V8 compact roadster is good for a benchmark 0-100km/h sprint of only 4.6sec while returning combined-cycleconsumption of only 8.4 litres/100km. Statistically, that makes the new SLK55 0.3sec faster and a substantial 3.6 litres/100km lighter on fuel.

For engine design anoraks, the new SLK55 V8’s trump card trivia is its direct-injection system’s 200-bar pressure rating – the highest of any non-turbo production engine…

BEST OF BOTH WORLDS: Beyond the SLK55’s dynamic engineering details the car’s hard top retracts (or folds over) in 20 seconds. There’s a glass roofed option for the first time, too…


Best of all, though, is AMG’s exhaust flap technology (a first for any Affalterbach machine) which debuts with the new SLK55.

Although an affront to automotive elocution purists, exhaust flaps are a necessary technical evil to ensure dramatic acoustics are balanced with contemporary European Union-mandated noise regulations.

The SLK55’s flaps are located in each of the 65mm diameter dual exhausts and open at varying increments (15, 30 and 50 degrees) depending on the duration of full-throttle driver input to authenticate its V8 soundtrack in the best way possible.

When the flaps open, exhaust gases cover a shorter distance and that characteristic V8 sound is writ large in a bellowing tone.

As more and more performance-car engines make the switch to turbo or hybrid power V8 options are becoming few and far between. With the new SLK55, AMG’s guaranteed its customers something unique in the compact roadster market.

Much like the original SLK55, though, one gets that nagging feeling that the decision not to allocate sufficient engineering resources to ensure a successful fit of the twin-turbo 5.5 V8 (much as was the case with the M156 6.2-litre V8) has more to do with preserving the SL63’s status than actual technical feasibility…


Although the SLK55’s V8 engine is very much its raison d'être, AMG’s engineers have ensured the dynamic package is well harmonised. Stiffened suspension components on all wheels, large brakes rotors (360mm front, 330mm rear) and clever torque-vectoring technology (where an opposing rear wheel is trail-braked into fast corners, to neaten the SLK’s posture and tighten its line) should combine to herald a (highly) rewarding drive.

For those who demand even more there’ll be an optional AMG handling pack adding composite brakes, AMG newfangled three-spoked steering wheel, (even) more rebound resistant suspension and a rear differential lock – the latter feature an essential for those keen on sliding the 310kW SLK55 around second-gear roundabouts...

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