@bullfrog – The reason that is, (someone please correct me if I’m wrong) but that they have been able to see the engine since it was first developed, meaning they can design the car around it, however non engine producing teams will see it later, so will already have had to build the car and thus have to slot the engine in. Basically Ferrari and Mercedes have the engines sooner than their customer teams, and so can design the cars around it sooner and for longer.