Which year did porsche introduce the 'Wide Body' design for the first time

1974 with the introduction of the 911 Turbo. It was also the model year that the cars got big bumpers.

1973 - the first ''wide body'' was the RSR ('73 also was the first year for the factory to offer the ''Carrera flares'' with the RS). Though the term ''wide body'' would not really be used until the Turbo Carrera in 1976. 1984 would mark the first year when the turbo body would be offered as an option on a car other than the turbo (turbo-look option, available for all Carrera models).