The Duster was a success for Plymouth, so much so that in 1971 Dodge requested and received their own version, the Demon. In response, Plymouth was given a version of the Dodge Dart Swinger 2-door hardtop named the Plymouth Scamp.
For 1971, only small changes were made to the Duster. The "Valiant" fender badges and "Plymouth" grille logotype were deleted. A new trim package was released, called the Duster Twister. The Twister package presented the appearance of the Duster 340, but came only with the base I6 or 318 V8. The Twister's appearance package included special side stripes that mimicked the Duster 340 Wedge stripes, a matte-black hood and the 340's special shark-tooth grille. A nonfunctional dual hood scoop and rear spoiler appearance package was available, as were high-back bucket seats and dual exhaust.
A new Electronic "Breakerless" Ignition became optional on the 340 V8 late in 1971 model year.
Source: Wikipedia, 2012