Um, it may require premium fuel but as a manufactured passenger car per US law it has to be able to run on regular and pass emissions while doing so. There are plenty of rentals that require premium per the manufacturer but are filled with regular every day. Even the supercharged Cobras can run regular on the factory tune, with a loss of performance but with no harm to the engine. Ford can require the use of premium, but can not deny warranty coverage if regular is found in the tank.