German carmaker Porsche on Tuesday unveiled the world's fastest sedan Panamera Turbo, which accelerates from 0 to 100 kmph in 3.6 seconds. Powered by a four-litre twin-turbo V8 engine, the sedan delivers 550 hp and has a top speed of 306 kmph. It will launch in January 2017 in the US at a starting price of $146,900.