New Lamborghini Fenomeno Roadster headed to Australia with a price tag rumoured to be more than $8 million

Creating the ultra-limited Lamborghini Fenomeno Roadster was no mean feat.

Despite looking like a gas-axed take on the wild Fenomeno Coupe, designers and engineers were forced to almost start from scratch in a labour-intensive process fraught with difficulties that pushed the car-maker to its absolute limit.

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Just 15 of the 794kW V12 roadster will be built, each are rumoured to cost more than €5 million (A$8.2m). The entire run is sold out, with just one open-air Fenomeno Roadster said to be heading to Australia, even though it will be left-hand drive.

Loosely based on the current Lamborghini Revuelto, the problems began for the skunkworks team because the supercar's carbon-fibre 'monofuselage' structure had never been designed to have its roof lopped off.

Effectively redesigned and strengthened to compensate for the alfresco driving experience, engineers used a new patented bonding fluid for the carbon-fibre, plus long and short fibres that ramp up rigidity. 

Modified front and rear crash structures have also been used, while a new cradle behind the driver and passenger seats enhance stiffness and side-impact protection, but it means the drop-top can't be offered with the coupe's full carbon-fibre race seats because there's not enough space to mount them.

Even with a heavy X-brace structure added to the engine, Lamborghini claims the roadster's structure weighs "only a few kilos more" than the one used for the coupe.

Once the foundations were set, designers attempted to tweak the coupe's styling for the roadster, but without a roof scoop the roadster's V12 was plagued by cooling issues. 

A complete redesign above the waist was the only option.

Tweaks you might notice are the reshaped longer windscreen rail that channels air carefully to an all-new engine cover, plus a pair of roll-over hoops that were honed in the wind tunnel.

Combined with the carry-over sharp lines, wide Countach-like air intakes behind the rear doors, aerodynamicists claim downforce has been boosted by 30 per cent, without any sacrifice in cooling performance.

Featuring an overall shape inspired by 1970s racing prototypes, the long-tail Fenomeno Roaster sports the same striking hexagonal exhaust pipe, a hint at the electrified 6.5-litre V12 that lies midship.

Tuned to produce a little more power 621kW (versus 607kW in the Revuelto) and 725Nm of torque, the V12 is still more than happy to rev to 9250rpm but is blended with not one, but three electric motors boosting power to a monstrous 794kW and 1075Nm of torque that is combined with an eight-speed dual-clutch transmission and channels its might to all four wheels.

Fitted with a larger 7kWh battery, that also provides for a 20km EV range, Lamborghini claims its roofless Fenomeno can launch from 0-100km/h in 2.4 seconds, 0-200km/h in 6.8 seconds, while top speed is a very blustery 340km/h.

Keeping weight down to a reasonable 1780kg, more fresh innovation reserved for the Fenomeno includes a Countach-inspired wheel design that saves an incredible 3kg per corner, plus Lamborghini's next-generation CCM-R carbon-ceramic brakes that employ discs made of long fibres embedded in a carbon matrix that's embalmed in a special coating and combined with 'organic' brake pads.

It helps that there's also zero weatherproofing, with designers shunning even an emergency roof. Should the heavens open you and the car's cabin will be soaked.

Speaking of which, the cabin is largely carried over from the Revuelto but with more options to personalise and customise.

It's a similar story for the body that is offered in unlimited paint combinations, the show car's hue is said to reference the colour of the first ever Lamborghini drop-top, the 1968 Miura Roadster.

Featuring a fully adjustable near competition-spec race suspension, the limited Lambo gets two bespoke Bridgestone tyre options that includes a semi-slick option.

Capable of torque vectoring, the Fenomeno Roadster bags the same advanced 6D sensor and vehicle chassis management the Revuelto sports.

If you're wondering why Lamborghini has made just 15 Fenomeno Roadsters, instead of the 29 Coupes, it's because the drop-top can't pass US pedestrian impact tests because of the new front crash structure. Engineers insist they could have come up with a fix but just ran out of time.

The rest of the know-how accrued from the Fenomeno Roadster project will soon be rolled out on future series Lamborghinis, with snazzy ultra-lightweight wheels primed to make a reappearance very soon on faster versions of both the Revuelto and smaller Temerario.