For a period spanning from 1977 through 1989 Dodge produced its Diplomat model into an influential mid-size car product. Dodge launched its new Diplomat coupe and sedan models in 1977 and completed the lineup by bringing station wagons to markets in 1978. The Dodge Diplomat offered three engine options starting with a 225 cu in (3.7 L) straight-6 followed by a 318 cu in (5.2 L) and then a 360 cu in (5.9 L) V8 engine. The standard power unit for the Dodge Diplomat consisted of the 318 V8 equipped with Lean Burn technology which produced 150 hp when launched. The 360 cu in V8 engine became an optional engine choice for the Dodge Diplomat in 1978 with a power output of 150 hp that continued as one of the available engines during subsequent years. The 1978 model series included a standard three-speed manual transmission alongside optional four-speed manual transmission for customers. The vehicle manufacturer switched to a three-speed automatic transmission as the standard system in 1983. According to the fuel economy specifications the Dodge Diplomat achieved a rate of 16 mpg in city driving while providing 21 mpg during highway operation. These figures depended on the model's engine type. Although the Diplomat existed with the same chassis as the Plymouth Aspen both cars used distinct body designs for their three model types including coupe and sedan and station wagon. The Diplomat was the final rear-wheel-drive vehicle that Dodge produced except for trucks before its 1989 termination.