As far as I am aware, supercars have a controlled chassis. Every one is the same underneath a plastic skin to reduce costs and thus pay the racing suit wearing commentators more $$. The plastic bodywork is mocked up to resemble whatever marque they are supposed to be. Engine must be from the manufacturer, but I suspect gearbox to driving wheels and braking systems are common as well. They (the w%$nker commentators) never discuss the technical differences between the cars, presumably because there are none.