Mercedes-AMG SLK 55

What is it?

The headline news here is that most exciting and rare of introductions; an all-new AMG engine, featured here in the new Mercedes SLK 55 AMG.

Mercedes’ go-faster department is being coy about where else the naturally aspirated version of its 5.5-litre V8 will be used. Here, it provides the flagship SLK 55 AMG with 416bhp and 398lb ft of torque. And, fitted with automatic engine stop-start, high-pressure direct injection, intelligent ancilliary power management and a clever cylinder deactivation system, emits 195g/km of CO2 and returns a claimed 33.6mpg on the combined cycle. Which makes the SLK 55 AMG the most fuel-efficient V8-powered production car in the world – as well as the only V8-powered compact convertible you can buy.

What’s it like?

That economy claim’s certainly not pie in the sky. On our test route, the SLK 55 AMG returned a remarkable 33mpg at a typical motorway cruise, and better than thirty-one to the gallon over a varied route. That was according to the car’s trip computer, admittedly, but in this tester’s experience, they now tend to be unerringly accurate.

Economy isn’t going to sell many new SLK 55s, of course. More important by far is the fact that this new engine is powerful, flexible and tuneful enough to satisfy any reasonable requirement of a performance convertible. Wide open, the powerplant gives the SLK high-rpm thrust significantly beyond that of an Audi TT-RS. Throttle response is predictably crisp, and the car’s gearbox is impressive too. Smooth and unobtrusive in ‘D’, and responsive enough in manual mode.

There’s more mixed news on the ride and handling front. The SLK 55 gets stiffer springs, dampers, roll-bars and bushings than the standard car, more negative camber on its real wheels and a more direct steering setup. Equipped with AMG’s optional handling pack (even stiffer chassis rates and a limited slip differential), our test car felt a little too firm over rougher surfaces. Standard cars might have a more comfortable ride, but it remains to be seen if they’ll provide the well-damped but absorptive chassis compromise that is so attractive, where everyday use is concerned, in certain rivals.

Better riding or not, no SLK 55 AMG – on this evidence – will have the precise body control and interactive, engaging drive of the class’ effervescent and evergreen dynamic standard-bearer – the Porsche Boxster S. Inconsistent steering weight, little steering feel, some noticeable low-frequency body pitch, and an otherwsie stable but inert and uninspiring chassis still ultimately separate this car not just from the Porsche, but at this price level, from the likes of the very sweetly suspended Jaguar XK.

Should I buy one?

If you like the idea of big open air performance without the usual penalty of sub 25mpg fuel economy, sure. The virtues of AMG Mercs often take longer than the usual test route to present themselves to the driver, and it’s very possible that this SLK would wind up being a highly satisfying car to own for all sorts of reasons.

But it’s still not a particularly engaging machine to drive, and even accounting for the other advances, keen drivers can’t fail to be disappointed by that.

Mercedes SLK 55 AMG

Price: £57,000; Top speed: 155mph (limited); 0-62mph: 4.6sec; Economy: 33.6mpg; Co2: 195g/km; Kerbweight: 1610kg; Engine type, cc: V8, 5461cc, normally aspirated; Power: 416bhp at 6800rpm; Torque: 398lb ft at 4500rpm; Gearbox: 7-spd automatic