Mercedes SL55 AMG

Talk about one-upmanship. No sooner has Mercedes' new SL been launched to rave reviews than the company's in-house tuning arm has gone one better. The SL55 AMG is the three-pointed star's new flagship, and the most powerful production car ever to storm out of the factory gates. But can AMG improve on the superbly accomplished SL500?

In a word, yes, although the sports specialist has wisely left the stunning styling and roof mechanism well alone. The car's shape is a masterclass in understatement, so external changes are limited to modified bumpers, four chromed exhausts and a choice of two new 18-inch alloy wheel designs. Few onlookers will be aware of the car's Ferrari-bashing performance potential lurking within the sculpted body. AMG's designers have been bolder in the cabin, but with mixed results. The new 'sandcast-effect' anodised aluminium trim is meant to imitate the crackle finish on the engine cover, but it looks cheap and feels rough to the touch.

The instrument pod is much more successful with the classic silver dials topped by a suede cowling. The seats have also been altered to feature contoured backrests with electrically inflatable side bolsters. They're incredibly comfortable and lock the body in place.

That's essential, given the SL55's performance. AMG admits that when developing the 5.5-litre supercharged V8 engine, torque was the primary concern. A supercharger is ideal as it operates at low engine speeds, and AMG had already developed the technology for the SLK32 and C32 models launched earlier this year.

But the SL55 is in another league, producing an astonishing 700Nm of torque at only 2,650rpm. Compared with that, its 476bhp power output seems almost insignificant. And the engine's sound is amazing. Even at idle, it reverberates through your ears and makes the ground tremble. Crack the throttle open and the full-blooded roar is nothing short of phenomenal.

However, it takes a while to notice the sound - to begin with, you're too busy concentrating on the speed. Despite weighing the best part of two tons, AMG's flagship will pass 60mph in 4.5 seconds. By that stage, though, it's only just getting into its stride. With the standard car's 155mph limiter removed, Mercedes claims 180mph is easily achievable. However an AMG engineer has admitted to us that an otherwise unmodified SL55 has already achieved over 205mph in testing! And this from an engine that meets EU-4 emissions regulations, which don't come into force until 2005. It's no surprise to find the power being channelled through a five-speed automatic gearbox. However, this one features a manual mode, with buttons behind the steering wheel. The only downside is that the buttons are rather easy to hit by mistake. Apart from that, it's great - the shifts are swift and perfectly smooth. The same goes for the driving experience. AMG models of the past used to be rather hard and brutal, but not any more. The SL500 is a phenomenal starting point and the SL55 moves the game on from there. It's not a pure sports car, and it's never going to offer a Ferrari-type thrill, but it is astonishingly capable and flows beautifully.

Yet it does have a flaw as a high-speed cruiser. While well heeled owners are unlikely to worry about the horrendous fuel economy (we averaged about 11mpg), they might be concerned about the car's range. Exploit the performance, and the fuel light will blink on after only 160 miles - hardly suitable for a grand tourer.

British prices have still to be announced, but expect the SL55 AMG to command a