The 1975 Duster models were mostly unchanged from the previous two years, with some exceptions: a new grille with a return of the Plymouth 3-pointed-'spear' affixed to the grille's center; catalytic converters were added to 225 Slant Six and 318 V8 models (the 360 was not equipped with a converter and its power was now 235 hp (175 kW), due to the addition of a secondary air injection system, commonly referred to as a "smog pump".

Source: Wikipedia, 2012