Mercedes-Benz SL63 AMG

Another tunnel, another irresistible opportunity. The roof is down, a couple of flicks of the left-hand paddle select the appropriate gear and, as we plunge into the semi-darkness, the hammer goes down. The sound is thunderous, soaring, physical, a mosh-pit heavy-metal wall of sound with a V8 bass beat. To the unsuspecting it must sound like the tunnel is caving in.

You don’t need to scare yourself silly like this to appreciate that the new 518bhp SL63 AMG firmly ticks the box marked ‘aural entertainment’. The rumble of its 6.2-litre V8 sounds great bouncing off buildings and creases your chops even at idle, the quad tailpipes emitting a spluttery, burbling pulse like a motor cruiser. In this respect, then, it’s a more than adequate replacement for the SL55 AMG, the car that until very recently was regarded by us at evo as the most desirable Mercedes in production (for an astonishing 75 issues it has been ‘Our Choice’ in the convertibles section of The Knowledge).

I’m pretty certain that for many buyers, as for us, a large chunk of the SL55’s appeal was the accessibility and generosity of its performance. In its final iteration the supercharged 5.4-litre V8 delivered a fulsome 508bhp, but the real impact was made by its ever-ready torque, a massive 531lb ft on tap from a ludicrously low 2600rpm. The SL55 could mooch effortlessly, folding metal roof stowed, or hack along at an impressive rate, responsive and composed.

The SL63 looks different, wearing the new, range-wide wide-mouth facelift. More importantly, right away it feels different, more sporty. Its town ride is more resilient, its transmission crisper and, out of town, its performance is of a quite different character. At 518bhp, the SL63’s naturally aspirated V8 offers a fraction more power than the old supercharged unit, but considerably less torque: 465lb ft, down 43lb ft. While this is still an impressive figure in absolute terms, it arrives at 5200rpm, just 2000rpm short of the rev limiter.

The cars we’ve tried most recently, with versions of this engine – the 500bhp CLK63 AMG Black Series and the 449bhp C63 AMG – have seemed more than adequately muscular, their seven-speed ‘AMG Speedshift’ automatic gearboxes helping to keep them on the boil. At nearly two tons the SL63 is a chunk heavier, so it’s perhaps appropriate that it should be the first to benefit from AMG’s latest gearbox innovation, designed to further enhance the response of the big-capacity V8.

A DSG-style dual-clutch ’box would have done the job, but AMG’s head of development and production, Wolf Zimmermann, explains that one beefy enough to handle the torque would have been much bulkier and heavier than the incumbent seven-speed auto. So instead, AMG has replaced the auto’s regular fluid torque-converter with a multi-plate clutch. As well as offering more positive shifts, this six-plate wet clutch is lighter (by 4kg) and smaller in diameter, reducing inertia and thus enhancing throttle response. Called Speedshift MCT (multi-clutch technology), it has taken three years to perfect, the challenge being successfully calibrating the all-important bite point so that the multi-plate clutch offers near-torque-converter smoothness at low speeds on a light throttle, but snappier yet still smooth shifts at full throttle. AMG’s confidence that it has succeeded is reflected in its claim that the clutch should never need replacing.

Four drive modes are selectable via a centre-console dial a little like Ferrari’s ‘manettino’. These manipulate throttle response and shift speed and range from ‘Comfort’ through ‘Sport’ and ‘Sport-Plus’ to ‘Manual’, which offers the fastest shift speeds of all at 100 milliseconds. There’s even a ‘Race Start’ function that juggles both the bite of the clutch and tyre slip to give the optimum standing start. Unlike the Ferrari’s holistic manettino, other functions such as standard or firmer ABC suspension and three stages of ESP stability control (full ESP, the slightly looser ‘ESP Sport’ setting or no ESP at all) can be dialled up separately and then, if you wish, memorised via the ‘AMG’ button.

Moving off, the SL63 feels more like an automated manual than a torque-converter auto, the bite of the clutch varying with the throttle input. However, once you’ve shifted into second there’s little to suggest that there’s anything but a regular auto ’box shuffling the gears. Meanwhile the steering is meatily weighted and the ABC suspension, firmed up over the cooking versions, feels less absorbent than the SL55’s, no question, but there’s an edge, a directness, that suggests a quite different experience to the out-going model.

Initially, it feels like it’s going to be a lesser experience. The instant gratification of the torque-rich SL55 is missing, despite seven gears (as opposed to five) and the sharper throttle response; you have to work the new engine hard, using lots of revs. However, while the start-of-day feeling was that the SL63 was a little ‘flat’ and not as exciting as its 518bhp rating suggested, by the time I handed the keys back I had been won over by its ability and consistency. The further you drive the SL63, the better it feels. The directness of its steering, the firmness of its chassis and the need to work its engine and gearbox hard ultimately fuse into a very satisfying experience. As ever, the active suspension helps disguise the SL’s weight, giving the car a neat, agile feel through a sequence of bends.

I loved the crispness of the ‘manual’ paddle shifts and the directness of the throttle response. And when we found a hairpin for the action shots and ran the SL63 up and down for a couple of dozen oversteer runs, the clutch performed without complaint. I can’t imagine an automated manual with a dry clutch would have done the same.

The ‘Sport’ transmission setting seems the best choice for everyday use, offering sweet upshifts and blip-perfect downshifts. The changes are marginally slower than those in Sport-Plus, but that setting seems a little less intuitive, holding gears a little too long and not allowing short-shifts via the paddles. Overall, though, Speedshift MCT works pretty well, but I can’t help thinking it will be more impressive in lighter cars like the C63 AMG or CLK63 Black Series.

While the SL55 was an SL that just happened to have an enormous and potent engine, and was surprisingly able when you used it, the SL63 is more obviously the sports car of the range. If you’re a keen driver, it’s a more involving and responsive car, but I expect that for many others it will lack the older car’s more rounded appeal.

Specifications