 Complete the following phrase:  Alfas engines were powerful, but had proved troublesome and according to Henry, the days during which pure power was the main criterion had temporarily vanished by the start of 1979. Instead aerodynamic ground effect, as brought to Formula One by the Lotus 78 two years earlier, was the most important factor. To allow them to focus on this, the Brabham team reverted to a known quantity, the reliable and widely used Ford Cosworth DFV engine that it had last used in 1975. Three BT49s were designed and built in only six weeks for the 