CARSCOOPS: The Cayenne Turbo GT retains the four-liter twin-turbo V8 that powers the Turbo Coupe, but does so with a power boost of 90 PS (67 kW/90 HP), giving it a total of 640 PS (471 kW/631 hp). Torque is up by 80 Nm to 850 Nm (626 lb.-ft) too. The bump in power isn’t down to a simple remap, as some may assume. Instead, Porsche…