'Uncompromising' is an appropriate word for the Aventador J. It's how Lamborghini describe their new chop-top roadster take on the mighty Aventador, a two-seater jet-fighter of a car. The company have done more than make a convertible from a coupé. In fact, they haven't made a convertible: the Aventador J has neither optional roof – nor windscreen! – and mostly is a relation to the Aventador in name only.

The 'J' name is derived from the FIA Appendix J regulations, which define the technical specifications of GT race cars: it's rather clear just what kind of car the Aventador J is supposed to be. Creature comforts and the little things that make driving hyper-cars in towns vaguely bearable have all been dispensed with: this is a car that exists for one purpose: to go fast. Extremely fast. 

The J is based on the 'regular' LP 700-4 and it utilises the same technology package of extreme materials and construction as its base. A monocoque made from carbon fibre-reinforced polymers is at the core of the J, the modified design of which is bespoke to this one-off model. Two safety bars behind the seats add extra protection and stiffness. 

The body shape retains the brutal geometric, Stealth Bomber-style angles of the coupé, and it's still a very big car: almost five-metres long and over two metres wide – yet only just over a metre high! The nose is narrower than the coupé, and dominated by the distinctive carbon fibre air scoop, which has central fixing braces and upward tilting winglets on the outside edges.

At the rear, it's all about the huge wing and diffuser, quad tail-pipes and distinctive Y-shape tail-lights. The main surface area at the back is used for heat dissipation and is covered by a thin metal mesh.

The doors open upward and are much thinner than the Aventador – they do actually feature small, fixed glass screens. The rich chromed red paint colour is again bespoke to this model: the colour makes the car look even more aggressive, and counterpoints the enormous amount of pure black carbon fibre that's used in the car.

The wheels were, of course, also specially developed for the J: 20" rims at the front and 21" at the rear, the five-spoke wheels have a central locking system and additional carbon fibre inserts that function as small fans for optimum brake ventilation.

Dry weight is 1,575kgs: the J is all about saving weight. To start with, of course the roof has gone; the air-conditioning is also stripped out and the cockpit facilities reduced (GPS? Nope. Use a map. Audio system? That's what the V12 is for). The seats are made of a forged composite with inserts of soft, flexible carbon fibre; in fact, the entire cockpit has been finished with this bespoke development of carbon fibre that Lamborghini call Carbonskin. 

The engine is a new 12-cylinder, 6.5-litre unit developing 700hp at high revs through a lightweight seven-speed automated transmission – openings on the rear carbon deck lay the cylinder banks open to view. The car has permanent four-wheel-drive and F1-style pushrod suspension for optimum handling.

There is just one Aventador J: so just one lucky owner will be driving this around. And let's hope it is driven around, and not consigned to some air-conditioned collection somewhere. Seeing this car in the flesh would be one thing – hearing it would be quite another.

Jonathan Moore

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