There seems to be some kind of electrical problem behind the Brabus S V12's dashboard. The wire from engine to tachometer has clearly shorted with that from gearbox to speedo, because when we accelerate flat-out in this 640bhp Mercedes SL600 the needles on both instruments flick across their dials at the same rate. I jest, but only slightly. They almost do.

With the possible exception of the 1988 Le Mans-winning Jaguar XJR9 and a dragster powered by a jet engine, this is the most powerful car I've ever driven. At 1750rpm it develops 757lb ft of torque and would develop a large chunk of that even further down the rev-range if Brabus hadn't programmed the engine management to pin the torque back a bit to save the powertrain, the rear tyres, your no-claims bonus and the world.

This is what they do at Brabus's factory in Bottrop, in Germany's industrial Ruhr. A fully-loaded SL600 is ordered from Mercedes-Benz. The engine is then hoiked out and completely stripped down. The cylinders are bored out to 83mm and a crankshaft with a 96mm stroke is ordered from a specialist crankshaft manufacturer in the UK because, says Brabus, the Brits make the best cranks (they should see the British crank at evo who has spent ΂£30,000 on a Ford Capri). In go 12 steel conrods (Made in England) and a dozen 9.0:1 compression ratio German Mahle pistons. That little lot brings the cubic capacity up from 5.5 to 6.3 litres, which is a nice number if you know your M-B performance history (yes, the late '60s 300 SEL 6.3). Different camshafts are fitted and the engine management is re-written, along with countless other honings and fettlings. The result is an engine that cranks out 640bhp at 5300rpm - and costs ΂£27,500.

The standard five-speed automatic is pulled apart and fitted with stronger clutch packs, then popped back in again and an oil cooler fitted. You can see it through the bespoke Brabus front skirt on the front offside of the car. The differential on this car is standard SL600, but Brabus is developing a full-on lsd that will slip less than the standard unit.
The Brabus S V12 looks seriously gangsta in black. The wheels are Brabus's own 20in Monoblock alloys in 9J at the front and 10.5J at the back with rubber band-like 255/35 ZR20 and 305/25 ZR20 Contis front and back respectively. Ah, the tyres. These are the most suitable tyres that Brabus could come up with but unfortunately they're not rated above 310kph so the S V12 has had to be limited to only 194mph. This is a bit of a bugger if you're being hassled by an Enzo or a Macca, but don't fret too much over this detail because I can assure you that most other vehicles on the road are not going to be a problem.

Just a short squirt from Bottrop is autobahn A31. This is the Bonneville of Europe. It runs for about 35 miles and then finishes, just like that, in the middle of the countryside. The beauty of it is that you can stooge around at the end, waiting until nobody has joined it for a few minutes. Then you can take off safe in the knowledge that you'll have a clear run for a few miles to the first exit. The only snag is that the S V12 covers that distance in just a few moments.

We mentioned earlier that the SL600 base car is fully-loaded. We meant it. Heated front seats with cooling fans and the back massager gizmo, telly and nav, you name it, it's here. And all this lot brings the SL's weight from a standard 1915kg up to 2000kg. Do the sums and you'll see that this gives us a power-to-weight ratio of 320bhp per ton, which, as evo readers know full well, isn't that massive. Cut out some of that weight and the Brabus SL would manage an even better performance than its 0-62mph time of 4.3sec and 0-125mph in 13sec. But this car wasn't built to rule Santa Pod. Its trick is decimating everything on the autobahn from 100mph upwards. The initial acceleration from, say, 60mph is not particularly shattering by modern high performance standards, but how it continues to gather speed certainly is. Ever driven a Suzuki Cappuccino and seen how it rips to its limited 90mph and then stops? The same with the Brabus, except that it blasts to 190mph and stops. We do it loads of times. Slower car (and most are) gets in the way, brush the brakes; car moves over, squeeze throttle and we're at one-ninety again.

Sometimes, though, we have to more than brush the brakes. Two tons takes a lot of stopping. More anchorage than a factory set-up could manage, that's for certain. The S V12 uses 12-piston Alcon front callipers (another verse of God Save The Queen, please) and whopping 375mm discs, and four-piston callipers and 355mm discs at the back. Aral racing brake fluid is used because these mighty retarders get so hot that they'd boil standard fluid. A temperature strip on one of the front callipers has gone off the scale at 380 Fahrenheit. They struggle, but they do the job. Time and time again.

The A31 is beautifully smooth, which is a blessing because it only takes an errant ant strolling across the tarmac and under the Contis to send mighty shocks up through the tyres, through the seats and up through your cooled and massaged backside. Sven Gramm, Brabus's tyre-smoking PR man ('I'm not really allowed to burn rubber,' he says, 'but sometimes I misjudge the throttle'), looks horrified when I move to press the damping control button.
Apparently if you select the sport setting the ride firms up so much it's an instant visit to the spinal injuries clinic. And that's on smooth German roads. Then there's the traction control, which Brabus has the technical capability to disable (merely switching off a stock Benz's traction control doesn't remove Big Brother entirely) but doesn't since a large chunk of its business is repeat business and it's keen not to have any customers wipe themselves out. To further improve this already dynamically excellent car, Brabus re-programs the ABC suspension to lower the car 15mm.

It's mad, this car. Mad, beautifully engineered, both by Mercedes-Benz and Brabus, and gloriously excessive. Is it worth ΂£35,000 over the standard ΂£95,440 SL600? Well, if you do a bhp per/΂£ calculation it certainly is, especially when compared with a Ferrari 575 Maranello. And do you need 640bhp when you can already get an SL55 with 493bhp? Just remember, when the pedal hits the firewall you've had what you've got. Better be sure it's enough.