This car weighs about 95kg less than a standard M3 due to the carbon-fibre honeycomb sandwich and glass-fibre thermoplastics used in its construction. Bearing in mind all the effort the 'M-gineers' have gone to to reduce weight, at 1,425kg the M3 CSL light for a steel monocoque car, but it isn't likely to blow away in a wind.

It has a new front skirt plus a revised intake system and engine management, that combine to up power a tad to about 350bhp. I'm told it has revised rear suspension, a wider track, bigger, 19-inch wheels, grippier tyres (Michelin Pilot Sport Cup), more direct steering and bigger brakes with reprogrammed ABS and DSC traction systems. There's a subtle bulge in the carbon-fibre bonnet too.

Casting an eye around the interior I note that the centre tunnel between the front seats is carbon fibre and, while there are electric windows (front and rear), there's no sunshine roof cut into the carbon-fibre roof, no aircon, no radio/cassette/CD player, no electric/heated seats, no leather (except on the wheel rim) and definitely no satnav or cruise control. I also note that there's now just a hint of mist appearing on the screen so, having blasted it clear, I open the rear windows, adjust the vents and whack up the fan speed.

I also know what a standard M3 feels like on this circuit because just 10 minutes earlier, and in the same damp, patchy conditions, I'd driven right up to the ragged edge in one. It felt good - powerful, fast and fun, with strong brakes and ample grip, certainly in the drier corners. But what I didn't know, and frankly couldn't have guessed, was quite how different and yet more rewarding my short CSL track test was about to be.

The first section of the circuit has changed dramatically since I was last here; the first corner is now a sharp, downhill, off-camber right-hander, but before I get there, I realise I could've braked much harder. I turn in, and realise I could've braked less. After just a couple more corners it's very apparent that the CSL will stop quicker, turn in more sharply, understeer much less, grip harder and communicate substantially more through the wheel. Its reprogrammed sequential gearchange shifts faster, its revs build quicker, while its DSC traction system seems much less eager to interrupt the seamless power. I'm already plainly going quicker by a margin than I did in the standard M3, but I feel more confident, more in control.

At first I wonder whether the track's now much drier than it had been, but after a full lap I realise that it's pretty much the same, and that it's the CSL making the difference here, though at the far end of the course there's now an obvious dry line appearing.

And while I'm thinking about all this, sweating inside my helmet, going as quick as I dare while trying hard not to be the first journalist to prang a prototype M car, I'm also having to mentally block out the electrifying noise. Being a complete sucker for sweet-sounding internal combustion is one of my lesser weaknesses and I know that if I allow my brain sufficient freedom to fully appreciate the mechanical melody, I'll probably miss my next braking point (if I could get a proper handle on where it is), and plough unceremoniously across an acre of trackside kitty-litter. That said, I can reveal that the straight-six CSL sounds guttural, urgent and crisp as a freshly-fried poppadum. Its bark is loud and hard and, like a Lamborghini V12, it doesn't have the synthetic timbre of some sports/ supercars I could mention. No, the noise of the CSL is real, not engineered, but I fear that, by the time this car makes production, it won't be allowed to sound quite so sharp.

My few laps are soon up. I've done my best. I've taken the neatest lines, braked as late as I dared, accelerated as hard as she'd go (0-60mph has to be comfortably in the four-second bracket), nibbled at the 8,000rpm rev limiter, ABS and DSC systems, and regularly topped 140-something on the back straight - still far from the car's real top speed. I tell you, I've had worse jobs. But now I'm back in the pit lane, engine silent, tyres still hot, brakes hotter still. That was good. I know that on a dry track and with a real racing driver, the CSL would probably exploit another dimension beyond where I can take it, but hey, it still treated me just fine.

As mentioned, the CSL here is a prototype and news of its existence was released a few months ago (see TG 101), but it has now been confirmed that it will go into limited production. That said, it's unlikely to reach dealers for at least another 18 months or so. Not least because BMW M people are still some way off deciding the final spec of the car. So now isn't the time to ask whether, firstly, it'll be officially on sale in the UK, secondly, whether it'll be in RHD and thirdly, how much will it cost? Because I can only answer: hopefully, probably not (E30 M3s were all LHD), and possibly around £50,000. But by then will it still have electric windows, as an option or standard? Time will tell. And although these cars were fitted with rear seats, they were very inaccessible and there's even a groundswell of opinion which says the CSL should be a two-seater as standard.

Tom Stewart

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