All A-bodies, including the Grand Prix, were redesigned for 1973. This generation was larger and heavier, due partly to the federally mandated 5 mph (8.0 km/h) crash bumpers. Although large V8s were still available, performance was on the decline due to another federal standard—a new emissions control system. The most notable styling feature of this generation was the appearance of the fixed opera window, replacing the previous disappearing rear side glass.