The base, or standard, 1965-1966 First Generation Ford Mustang was introduced in early 1964. Although Ford never officially built a 1964 model year Mustang, these early examples are commonly referred to as "1964-1/2" Mustangs, while cars built for the 1965 model year are known as "late 1965" Mustangs. The first Mustangs to roll off the line were only available in Hardtop or Convertible body styles, with a Fastback joining the lineup officially when the "late 1965" cars were introduced in August 1964. The 1965-1966 Ford Mustang was built with a wide range of inline six and V8 engine options, each of which were given a unique letter code to help in identification. Over the course of its production, the 1965-1966 Ford Mustang was available with the "U-code" 170 cubic inch (2.8L) inline six, "T-code" 200 cubic inch (3.3L) inline six, "F-code" 260 cubic inch (4.3L) V8, "D-Code" 289 cubic inch (4.7L) four-barrrel carburetor (210hp) V8, "C-code" 289 cubic inch (4.7L) two-barrel carburetor (200hp) V8, "A-code" 289 cubic inch (4.7L) four-barrel carburetor (225hp) V8, and the top of the line "K-code" 289 cubic inch (4.7L) 'HiPo' (271hp) V8. The "U-code" inline six and "F-code" V8 were only available on the unofficial 1964-1/2 cars, and these engines were replaced by the "T-code" and "C-code" engines respectively. Depending on the engine, the Mustang was available with a 3 speed manual, 4 speed manual, or 3 speed automatic transmission. A sportier version of the Mustang known as the Mustang GT became available for the 1965 model year. Cars fitted with the GT Performance Group (only available with a V8) featured various interior and exterior cosmetic changes, as well as the addition of disc brakes. For 1967, Ford updated the Mustang with the introduction of the 1967-1968 First Generation Ford Mustang.