The G model was built for around 25 years, during which time numerous changes were made to the series. Starting with 2.7 liters, the displacement of the naturally aspirated engines gradually increased to 3.2 liters. The proportion of chrome-plated parts on the bodywork fell to zero over the course of the production period, and even the Targa's bar was black on all vehicles from autumn 1979. From model year 1981 – recognizable by small additional indicators attached to the sides of the fenders – not only the load-bearing sheet metal parts were galvanized, but the entire bodywork. Porsche extended the guarantee against rust from six to seven years, and in 1986 even to ten years. The 911 Turbo, introduced in 1975 and the fastest production vehicle at the time, made automotive history.