The Riviera was introduced on October 4, 1962, as a 1963 model, with the 325 hp (242 kW) 401 cu in (6.6 l) "Nailhead" V-8 as the only available engine, fitted with dual exhaust as standard equipment, and the turbine drive the only transmission. Changes for 1965 included the introduction of the "Gran Sport" option, which included the dual-quad Super Wildcat 425 V8, a numerically higher 3.42 axle ratio, and stiffer, heavy-duty suspension. The stock dual exhaust pipes were increased from 2.0 inches (51 mm) to 2.25 inches (57 mm) inside diameter and had fewer turns to reduce back pressure. The 401 cu in (6.6 l) V8 returned as the standard Riviera engine and the Super Turbine 400 transmission retained the variable pitch torque converter, but was fitted with a three-speed gear selector. Externally, the headlamps were concealed behind clamshell doors in the leading edges of each fender, as in the original design. Further back, the non-functional side scoops between the doors and rear wheel arches were removed, and the taillights were moved from the body into the rear bumper.
Source: Wikipedia (original)