|The J Roadster is a roofless, V12-powered supercar which is powered by a 6.5-liter that is capable of delivering a total of 700 HP. Top speed goes up to an impressive 186 mph - a little less than the standard Aventador, but the J has to take into account it’s missing roof. It makes extensive use of carbon fiber, including a patented material called "carbon skin" for the interior. The car is so extreme that the driver must wear a helmet, though the car can be registered for road use, Lamborghini says. Lamborghini Aventador J sells for $2.8 million.