DRIVEN: MERCEDES SLK55 AMG
Does a big V8 make the SLK a credible driver's car?
The Mercedes SLK55 AMG - it's a hairdresser's hot rod, right? Well, the last Affalterbach example I drove was the original Black Series; an evil-handling thing with a fixed roof and 400hp. This new, non-Black Series SLK55 AMG is based on the third-gen car and deploys no less than 422hp.
Engine first. Given the familiar 5.5-litre capacity you get no extra fuel tokens for figuring out this new 'M152' V8 is closely related to the 'M157' bi-turbo that's been replacing the old 6.2-litre NA in bigger AMG Mercs since last year. Based on the same block, the M152 obviously gets a new air intake arrangement, but also new cylinder heads, modified valve drive, changes to the oil supply system and an 'optimised' aluminium crankcase.
In fact, it makes the M152 the most efficient V8 engine in the world right now. Yes, AMG does world-class efficiency.
Clearly, there's more than an upgraded alternator and starter motor assembly at work here. Which is where AMG Cylinder Management comes in. This cylinder deactivation trick, as previously seen on some American gas guzzlers, shuts down cylinders two, three, five and eight in a light-load situation between 800rpm and 3600rpm. Modern F1 cars do similar to save fuel in the pit lane, when stuck behind the safety car, and apparently even during slower cornering.
You're probably wondering what a V8 running on four cylinders sounds like, and to a certain extent so am I - because AMG has also taken the 'emotional sound design' a stage further with the SLK's exhaust system. For the first time on an AMG it includes "variably activated" flaps in the rear cans, which actually make the car damn near silent at a motorway cruise, even with the roof down. But listen hard when ECO4 is aglow before nudging the accelerator until it becomes ECO8 (something else that goes away in S and M), and you'll detect a deep drone becoming a deep burble.
But find a twisting road - and these were surprisingly plentiful along the Californian launch route - and some unexpected things happen. The engine isn't quite the dominant force in the SLK's package you might imagine; with no twin-turbo torque it needs working hard to really flatten you into the seat back, which, while arguably in keeping with the roadster spirit, does occasionally leave you wanting for decisiveness.
The AMG Speedshift Plus 7G-Tronic 'box does a generally decent job, but it's the chassis that should have you raising your eyebrows. Stacks of (dry) grip, a flat attitude that's unfazed by alternating cambers, and a notable degree of compliance make short work of switchbacks and sweepers - AMG's "Direct-Steer" modifications to the front end complimented by "Torque Vectoring Brake" at the rear. This tweaks the inside back wheel to deliver sharper turn-in rotation; McLaren has a similar system on the MP4-12C.
The SLK55 AMG may not prove to be the most enduringly engaging roadster on the market. But it's now a very well-rounded product, spreading itself across a range of talents instead of just letting rip with a big gun. Progress - but here's hoping AMG doesn't take this new-found finesse too far.