For 1970, the Valiant was carried over with detail changes, including a new black plastic grille sculptured differently from 1969's metal item. The central portion protruded flush with the forward edge of the hood, while the remainder of the grille was set back from the front plane. The two-door sedan was dropped, replaced by the new Duster coupe. For all except export Valiants, the base 170 engine was replaced by a new 198 cu in (3.2 L) version of the Slant-6. The 198 gave better performance than the 170, and was less costly to make, since it used the same cylinder block as the 225. The Valiant was virtually unchanged for 1971; small revisions included removal of the center grille emblem and a new kind of finish treatment on the grille surround. It now had a blacked-out look instead of the previous argent silver treatment. For the 1970 and 1971 models, exterior and interior trim were slightly revised, and there were engineering changes for better driveability, improved soundproofing and decreased emissions, the latter in compliance with regulations mandated by the newly created Environmental Protection Agency (EPA) implementing new devices such as an EGR valve and an activated charcoal filter. The 1971 Valiant eventually set sales records with 256,930 calendar year deliveries, so there was little motivation to change it for 1972. Only details of the taillights and grille were altered for the 1972 Valiants. New surface-mount sidemarker lamp-reflector units replaced the more costly previous flush-mount items.
Source: Wikipedia, 2013