Look longingly. This is one of just ten 170bhp twin-turbo Smart V6 Roadster Coupes constructed on behalf of Smart by Brabus. It's been engineered for effect rather than practicality - in place of the front boot sits a hugely expensive F1-spec foam-filled fuel tank, and if you want to change the spark plugs you have to drop the engine out - so when Smart says it has no plans to productionise the car, the claim rings true.

Shame. For starters, the V6 Roadster Coupe unleashes an even more aggressive visual punch than the standard car. First thing you notice is the Ferrari F40 treatment for its glazed back end, with ventilation slats cut into the Perspex side windows and some of the engine and turbo pipework visible through the tailgate window. A further sense of purpose is created by the V6's super-fat wheels and tyres, deeper front spoiler, aerodynamic black rubber 'moustaches' on the nose, and revised rear valance. It looks a bit like a BMW M Coupe, but with superior proportions.

Mercedes designed and built the Smart's 1396cc V6 engine in only a matter of months. Essentially it's two Smart 698cc three-cylinder motors united at 60deg and joined by a common crank in a unique alloy block. With specially fabricated intake and exhaust manifolds, twin-turbos and a water-cooled intercooler, output is 170bhp at 5500rpm with 162lb ft of torque from 2250-4500rpm.

Impressively, the extra hardware adds only 60kg to the Roadster's 790kg kerb weight, making the total little more than an Elise. With a power-to-weight ratio of 218bhp per ton, Smart's claims of 0-62mph in under 6.0sec and a 137mph top speed seem perfectly feasible.

Helping to deploy more than double the standard power are the same 7in and 8in Brabus alloys and broad Michelins you can buy for any Smart Roadster. Through their polished spokes you can spy Brabus-Alcon drilled and vented discs clamped by standard callipers up front and a bespoke pair at the rear. As further proof of how seriously Smart has taken this project, the Roadster's standard rear suspension (separate springs and dampers) is replaced by coil-over struts.

The V6 Roadster feels special straight away. Drop into the great-looking cabin, ease into the Sparco seats, slip on the four-point race harness, turn the transmission tunnel-mounted ignition key to 'On', and press the 'Start' button on the centre console.

Vroom! An unfamiliar sound fills the air behind your head, an engine note like no other, an intoxicating mix of V6, Smart three-pot and Porsche flat-six.

Select first with the gear lever and from then on you use the steering wheel paddles. The V6 Roadster scorches off the line with an urgency that can catch you unawares initially if your brain is still configured for the normal Smart Roadster experience.

Rapid acceleration in first, lift the throttle slightly as you pull the right paddle and the bespoke software swiftly selects second accompanied by the full symphony of psst, psst noises as the twin-turbos blow off excess boost. Same again for the next three ratios and we have completely outrun the traffic. Coming back down the 'box (a five-speeder soon to appear in the diesel-engined Smart ForFour) is also a hoot as the electronics blip the throttle, perfectly smoothing each downshift, all the way down into first as you come to rest.
The ride is firm but well controlled and the uprated suspension provides near roll-free cornering. The non-assisted steering is heavy at parking speeds, but lightens up on the move to a near perfect weighting. Where the production Roadster feels a bit slow-witted through corners, the newfound grunt allows you to throttle-steer the car and explore a previously hidden dimension of the excellent chassis.

The mere existence of the V6 Roadster shows that Smart has taken to heart its new corporate slogan 'Open Your Mind'. These ten prototypes are rumoured to have cost around ΂£330,000 a pop, but one we saw, bearing the autographs of David Coulthard and Kimi Raikonnen, is probably worth a bit more.