The 53 donkey is a 3.0-litre, and of extraordinary complexity. Deep breath. It’s an in-line six-cylinder petrol, mounted longitudinally, all of whose exhaust outlets pass through a single, large, twin-scroll turbocharger, mounted high and near as damnit next to the exhaust ports. To cover the inevitable turbo lag from this, though, there is also an electrically powered compressor, located on the other side of the block, just before an intercooler right next to the inlet ports, which can help suck air through the induction tract before the big turbocharger is boosting properly. Following? Good.
The inlet for that compressor comes after the big turbo, where a variable stopper in the main inlet tract, which runs around behind the engine, can divert a little, or all, or any combination – in reality, it’ll be varying the proportion constantly – of air through a smaller tube to the electric compressor, after which, suitably pressurised, it flows back to the main inlet tract just before a throttle butterfly. Still following? Sigh, me neither. Anyway, it makes 429bhp and 389lb ft, which is quite a lot in itself.
But in addition to both of these forced inductors, mounted between the engine and the nine-speed automatic gearbox sits an integrated starter/generator (ISG), an alternator/starter motor and flywheel combo, which can contribute 21bhp and no less than 184lb ft to the engine’s already imposing output. But rather than it just spinning up to reduce turbo lag, which doesn’t necessarily help increase pressure into the intake system, it’s apparently just as useful for it to drag slightly at low revs, developing electricity as it does, which it passes on to the electric compressor, and it’s that which spools the inlet pressure by dragging air through the turbo, helping that to spin up as it goes, too, thus reducing overall lag instead. Right? Look, I don’t know, my head hurts. I suppose the short of it is that getting air through the engine is key, so inlet pressure rather than engine speed itself is king.
Ultimately, though, all of this power goes to the CLS’s rear wheels most of the time, with a standard all-wheel drive system on all models diverting it to four wheels when the rears threaten to slip. Unlike, say, the E63 AMG, you can’t lock the 53 into rear-drive mode for adolescent slides.
Which is perhaps just as well. Our drive takes place in Spain during the first time for about a decade that it has experienced snowfall. So our CLS53 is wearing winter rubber, which, AMG engineers tell me, will reasonably well soften the way it grips and steers.
One of the challenges of the 53 was, by all accounts, to make it feel sufficiently different from a regular CLS to satisfy AMG boss Tobias Moers, who’s quite particular. Full-fat AMGs do have quite a distinct character: they’re loud, brash and way more capable these days than the hot rods they were a decade or so ago but still dominated by their V8 engines.
That’s a harder character to inject with a straight six, obviously, especially one whose exhaust is so muted by turbo and which, by definition, is a bit semi-skimmed next to a 63. But the engine is sparky. It’s by no means loud, but throttle response and linearity really are exceptional, with a rev limit at nearly 7000rpm and a character and note that has shades of BMW M car. It’s a belting engine, in fact. I wonder if Aston Martin, part owned by Daimler as it is, has thought about one day dropping one into a Vantage.
And if regular wheels and tyres – 20in and 21in will be most buyers’ norms, you suspect – sharpen the steering over these winters, it’ll be intensely responsive for a big saloon. Okay, okay, big coupé. Because accuracy and steering response are already great. It’s probably more responsive to the steering, I’d say, than a BMW M5, while standard air springing brings a level of both control and compliance where coil springs tend to force a compromise to one or the other; only this comes without the echoey ‘sproing’ that affects some bagged suspension.
Air springs, although optional rather than standard as they are on the AMG, were also fitted to the two other CLSs I’ve tried. A 400d, with a 3.0 straight six diesel and 335bhp, is wickedly fast, while a new four-cylinder petrol, arriving later, is not, being quite growly although with handling improved yet again by having a lighter engine in the nose. Both, also, use an ISG (which Mercedes dubs EQ Boost) so throttle response is fab and letting the auto ’box lug it out, rather than changing down yourself, is the easiest way to make good progress.
Whatever donkey your CLS comes fitted with, though, makes no difference to the way it feels inside, which is little short of excellent. In overall cabin layout and ergonomic decency, things mirror the E-Class here: the driving position is spot on and dead straight, with hugely adjustable wheel and clear, digital instrument panel, plus central monitor. Wiper and indicator stalk to the left, gearlever to the right, controls for one of motoring’s better infotainment systems on the centre console.
Material finish is great but it’s the vents that are coolest – steampunky-turbine-looking things that bask and reflect the glow of their own diddy central LED mood lights, in low light. Really lovely. Head room in the rear is, obviously, a bit tighter than in a conventional saloon, for the passengers you probably won’t have anyway, and the boot’s of a similar ‘yeah, fine, whatever’ capacity. If it’s not big enough, there’s always the E-Class, y’know?