The Smart Roadster Brabus is one of my favourite cars. The miniature mid-engined marvel is light, agile, direct, involving, and offers a sensation of speed second only to a skeleton bobsled. However, there are two things that the car is not: powerful or fast. While filming the B-road section for my video on the Roadster, I was consistently left behind by the camera car.

Not that it mattered too much, because I was having a whale of a time, feeling like I was doing the speed of sound when, in reality, I was barely touching the speed limit. However, the most powerful Smart Roadster to go on sale wasn’t the first one to be tuned by Brabus.

The story goes that, in 2003, Smart management were discussing the performance potential of their new Roadster over a few beers. Having launched with a choice between a 59 or 79bhp 0.7-litre three-cylinder engine, it was clear that the car could take more power. Thus, project PD6TF was launched in conjunction with tuning firm Brabus.

Instead of taking the easy route to higher performance, Brabus and Mercedes-Benz took two 0.7-litre engines and merged them at 60 degrees, creating a truly unique 1.4-litre biturbo V6. The head design was mirrored and attached to a bespoke crankcase, with the turbochargers on the outside of a custom-machined block. Maximum boost of 1.4bar was achieved, and power increased to 168bhp at 5,500rpm, while 162lb-ft (220Nm) of torque was available between 2,250 and 4,500rpm. The 0–62mph time dropped to 5.8 seconds, and the top speed rose to 137mph.

The engine remained transversely mounted behind the passenger cabin and sent its power to the rear wheels as before, but did so through a new five-speed automatic gearbox that was set to appear in the upcoming diesel-powered Forfour hatchback. Losing a ratio but gaining bespoke software, the ‘box could blip the throttle to make downshifts smoother. Some may ask why the team didn’t opt to fit a manual transmission during the conversion, but if you’ve ever tried to place adult-sized feet into the pedal box of a Smart Roadster, you’ll know there’s no room for a third pedal.

Further changes included a new intake, exhaust, coolant pump, water-cooled intercooler, and bespoke coil-over rear suspension, replacing the standard car’s De Dion setup with separate springs and dampers. Even the fuel tank was relocated to the nose of the car, with the F1-style foam-lined cell occupying the under-bonnet storage area. Owing to the short timeframe of the project – just four and a half months from beer to build – the V6 Roadster did without traction control, power steering, or ESP.

Based on the Roadster-Coupé model, the V6 Brabus introduced a brand-new bodykit with bespoke sills, bumpers, and a twin-exit exhaust at the rear. Further contrasting the regular Roadster, the V6 Brabus gained a body-coloured spoiler and front bumper insert, along with a pair of diveplanes on the nose, 17-inch wheels, and disc brakes at each corner. To aid cooling, the side windows were switched for ventilated perspex. Weight increased from 790kg to 850kg, but the car still boasted a power-to-weight ratio of 198bhp per tonne – ever so slightly more than the Porsche Boxster of the same era.

Inside, the seats were switched for diamond-stitched leather and Alcantara-clad Sparco buckets, complete with four-point harnesses, and a fire extinguisher on the passenger side. Enlarged metal shift paddles were attached to the new steering wheel, replacing the plastic ones from the production Roadster. Red trim sat around the four gauges, at the base of the gear shifter, and the central ignition barrel, while a commemorative plaque covered the gap left by the absent air conditioning and CD player, housing the starter button and displaying the build number instead. Only 10 of these super-roadsters were built, each one by hand, with the first one costing an estimated £330,000, while the remaining nine cost £75,000. Adjusted for inflation, that’s £582,000 and £132,000 respectively.

The cars were never meant to be static showcases but a functional proof of concept for a high-performance Smart. The V6 Roadster was showcased at events and delivered to the press to experience firsthand, with the car’s most famous appearance being at the hands of Richard Hammond on Top Gear, who described it as “a bottle of sportscar concentrate.” Writing for MotorTrend, Georg Kacher said it was “commendably nimble and chuckable” – adding that its “evenly balanced weight distribution gives it the handling of a slot car with a central guiding pin.”

In Evo Magazine, Ian Kuah wrote, “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.” A year later and also writing for Evo, Richard Porter said, “Overall the V6 has a distinctly meatier, more aggressive feel that would play well in the standard Roadster. I guess it's what happens when the car becomes more Brabus, less Smart.”

Although it was impressive, the V6 Roadster was never destined for the showrooms. The bespoke and complex V6 engine needed to be removed from the car in order for the oil and spark plugs to be changed. Of the ten that were made, it is believed that only three remain in existence. The six-cylinder Smart did pave the way for a series production Brabus model to follow. In 2004, it arrived with the bodykit and wheels of the V6 but a three-cylinder engine behind the cabin packing 99bhp and 99lb-ft, offering 62mph in 9.8 seconds and a top speed of 118mph. The production version also came with traction control, air conditioning, a CD player, and storage space at both ends, unlike the V6 prototypes.

The style of the biturbo Brabus did eventually make its way to the road with the RCR Edition of 2005. Each of the 50-strong production run featured the same red and silver colour scheme with a black and red interior inspired by the V6 models. Confusingly, the RCR models were based on the 79bhp non-Brabus Roadster, but a power upgrade to 89bhp was a no-cost option.

Smart Roadster production ended in late 2005 – the sheer volume of warranty claims against the model. In the following years, the car became known as the “Leakster” owing to its often porous roof. That said, the unique two-seater has gained a cult following, with a passionate group of owners past and present singing the praises of the car’s handling and character.

In Brabus specification, it is one of my favourite cars, feeling like a mixture of a modern Mini and an Audi R8, owing to its combination of rapid steering and mid-engined balance. However, I have to agree with the brains behind project PD6TF, who knew that the car would make good use of more power, more cylinders, and more turbos. The Smart Roadster Brabus V6 Biturbo showed what the car was capable of, but the world wasn’t ready for a Smart that had the same power-to-weight ratio as a Porsche Boxster – and a similar price tag to match if it entered series production.