Mercedes-AMG SL43 launched with 381hp

New entry-level model gets M139 four-pot - with an electric turbocharger for good measure

No matter what you thought of the all-new Mercedes SL's styling, there seemed little doubt that it was launching with performance to spare. No surprise perhaps, with Mercedes-AMG in charge of the model's development, but the 476hp SL55 and 585hp SL63 - both powered by the familiar 4.0-litre twin-turbo V8 and driving all four wheels - left little to the imagination. And probably positioned the car well beyond the mindset of most 2+2 convertible buyers.

The entry-level follow-up then, rather unsurprisingly, is intended to fill out some of the space beneath the petrol-quaffing flagship variants. For one thing, the new Mercedes-AMG SL43 is exclusively rear-drive - which is nice to read in this day and age - and, for another, it is powered by a 381hp 2.0-litre four-cylinder petrol engine. It won't shock anyone reading this to learn that it's the ubiquitous M139 unit which has been mounted longitudinally in the SL - but it's interesting to note that AMG has gone to the trouble of significantly sprucing up the motor with a brand-new electric exhaust gas turbocharger.

Now, Mercedes says this is the first time 'in the world' that the tech has been deployed in a production vehicle - which does stretch credibility a wee bit given a number of cars which have dabbled in electric turbocharging recently - but the manufacturer is likely referring specifically to the engineering principle it is using, one said to be directly derived from the technology employed by the brand's F1 team.

Where previous incarnations might have used an additional compressor, in the SL an electric motor around four centimetres wide is integrated directly onto the turbocharger shaft between the turbine wheel on the exhaust side and the compressor wheel on the intake side. As you might imagine, this electronically controlled motor is used to drive the shaft of the turbocharger before the exhaust gases start to spin it conventionally.

The result, at any rate, is much the same as elsewhere: significant improvement of throttle response from idle, and indeed across the rev range. Mercedes says it also enables higher torque at lower revs - although it's interesting to note that the SL's 354lb ft of peak twist isn't delivered until between 3,250 and 5,000rpm, which suggests that the manufacturer has opted for a more progressive build-up than might have otherwise been available to it.

AMG fans will also not need telling that the new SL mimics the power output of the previous generation A45, not the 421hp produced by the current one. This too is obviously a conscious decision, the manufacturer likely opting for the slightly more modest figure on the basis that in the SL's case it drives a single axle; not to mention the fact that it results in a 0-62mph time of 4.9 seconds, regardless. Delivering any more performance in the lighter, cheaper model might have had one too many customers wondering what exactly was the point of upgrading to the V8.

Before you answer that query in your own head, there's good reason to think that the SL43 will not want for refinement either. Thanks to the requirements of its dinky electric motor, the model gets a 48-volt electrical system - and because it's brand spanking new, it also benefits from a second-generation starter generator, which means a) it functions as a mild hybrid in glide mode, and b) it provides an additional boost of 14hp when the chips (or your right foot) are down.

Additionally, the whole shooting match is twinned with the latest nine-speed AMG Speedshift transmission for the first time, which means there are more ratios than ever for the engine to play with. AMG is promising 'extremely short shift times' from the multi-clutch unit, as well as multiple downshifts and an 'emotionally appealing' gearshift in the car's sportier modes.

Increased sportiness is, of course, this generation of SL's raison d'être, and there's no reason to think the SL43 will let the side down elsewhere. Aside from round tailpipes, slightly different bumpers and standard 19-inch wheels (naturally larger ones are available) the starter model will look much like its bigger-engined siblings - and there's even the option of an Aerodynamics Package if you feel like it needs eye-catching items like a larger rear diffuser.

Mercedes doesn't scream and shout about the 'distinctly discrete handling characteristics' of its entry-level model, but we're willing to bet that the 'comparatively light' four-cylinder engine and rear-drive makes a notable difference to a chassis that shares the all-round multi-link suspension of the V8 cars. It does without adaptive dampers or four-wheel steering (though both are options) so it will be interesting to see where the engineers have pitched the driving experience in what's likely to be the biggest-selling configuration.

Honestly, we have high hopes - especially if Mercedes prices the smaller-engined car to properly compete. There's no word on that just yet, although, when commenting on the launch, Philip Schiemer, AMG's chairman, was unequivocal about the model's broader significance.

"In its long history, the SL has repeatedly set technological milestones. For example, while the legendary 300 SL Gullwing in 1954 was the world's first series-produced passenger car with direct petrol injection, the new Mercedes-AMG SL 43 is now the very first series-produced vehicle with an electric exhaust gas turbocharger. With this technology, the SL also has an outstanding performance range in its entry-level version. This means that our seemingly smallest SL combines the typical AMG Driving Performance with luxury and comfort at the absolute top level. What's more, with this innovative engine we are undoubtedly also appealing to a wider clientèle."

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