The Riviera was radically redesigned for the 1971 model year with flowing and dramatic "boat-tail" styling. Designed under Bill Mitchell's direction, it was penned by Jerry Hirshberg, future head of design for Nissan, mating the two-piece vee-butted:792 fastback rear window, inspired by the 1963 Corvette Sting Ray split window coupe, to the Riviera's platform.
The design was originally intended for the smaller GM A platform, and the use of the Riviera's body—expanded for 1971 by 3 in (76 mm) in wheelbase and more than 120 lb (54 kg) heavier—produced controversial looks. (Collectible Automobile ran an article about 1971–76 full-sized Buicks in which one sketch design for their 2-door coupes which was rejected resembled the 1971–73 Riviera).
This generation introduced a much more visual representation of the "sweepspear", with a more faithful representation to the version that appeared on 1950s Buicks in both the side molding and beltline.
The 455 engine had a lower compression ratio to meet EPA emissions requirements, reducing power to 255 hp (190 kW), with 265 hp (198 kW) in the Gran Sport. Performance remained reasonably brisk, with a 0–60 time of 8.1 seconds for the GS, but the Riviera's sporty image was rapidly fading. One noteworthy advance was Buick's Max Trac limited-slip differential.[17] The 1971 Riviera also features GM's "Full-Flo" ventilation system and two large deck lid louvers are prominent on the trunk lid. (Unfortunately, under certain conditions a vacuum was created that sucked rain and exhaust back into the car and the "Full-Flo" ventilation was redesigned and the louvers were removed from trunk lid for the 1972 model year.)
Despite these features, Riviera sales for 1971 dropped to 33,810,[3]:798 the lowest to date. The 1972 Riviera was little changed, with the 455 engine switching to net power ratings, 225 hp (168 kW) or 250 hp (190 kW) with the Gran Sport, although the actual drop in net power was only 5 hp (3.7 kW). Sales remained moribund at 33,728.[3]:876 For 1973, the 250 hp (186 kW) engine became standard, with 260 hp (190 kW) with the Stage One package, which also included a limited slip differential and a chrome-plated air cleaner. The "Gran Sport" package was still available as a separate option package consisting of a ride-and-handling package that included a rear stabilizer bar, JR78-15 whitewall steel-belted radial tires, a specially tuned "radial roadability" suspension, additional sound insulation and special "Gran Sport" badging. Sluggish sales of the third generation Riviera led GM to believe that the boattail deck lid was too radical for most customers' tastes, so in 1973 it was blunted and made slightly shorter. The design change however only led to a marginal increase in sales, with 34,080 being produced for the model year.
