The longest-produced Mercedes-Benz model is the cross-country G-Class model, which entered the market in 1979. It has a permanent two-axle drive, a 5-speed, automatic gearbox, and now comes in three body versions, also with an extended wheelbase. Buyers can choose from 2.7-liter 156 hp or 4.0-liter 250 hp V8 diesel or 3.2-liter 215 hp V6 and 5.0-liter 296 hp V8 petrol engines. The most exclusive version, the G 55 AMG, is driven by a mechanically charged 5.4-liter 476 hp V8 engine, and furnished with a package of conveniences used in high class limousines. The G-Class model was designed in cooperation with the Austrian Steyr-Daimler-Puch company, and is produced solely at Austrian plants in the city of Graz.