If sloshing is a problem, the tanks have baffles. These are simple plates that stop the fuel surging across the width of the tank. Some cars don't need them and I'm not sure about Porsche. However, 30-40 litres of fuel surging across the car in a high g manoeuvre would probably be felt by the driver (soon after the turn is initiated) so I would guess the Porsche tank does have baffles.