The J denotes the J Roadster meaning of Roadster is a roofless, v12 is a powered supercar the power of supercar is 6.5 liter and it will give 700 horse powers and we can raise the speed up to 186 mph the difference between Aventador and Aventador J is a lighter changes with normal Lamborghini. In Aventador the roof is not present but in Lamborghini Aventador J the roof looks awesome. In outside layer the carbon fiber including the patented material inside is known as carbon skin. And the driver of the Lamborghini should wear helmet for the road use the market price of Lamborghini Aventador J is $2.8 million.