Porsche 911 Turbo S Cabriolet is the most powerful version of the 997 Gen II, featuring a 3.7-liter twin-turbocharged flat 6 engine that has 640 horsepower. The Porsche 911 Turbo S Cabriolet is a high-performance sports car that is part of the iconic Porsche 911 lineup. The “Turbo S” designation indicates that it is one of the most powerful and fastest versions of the 911.