An updated taillight design with three sections was the only major change to the 1986 Grand Prix. A new 2+2 model was offered for homologation of an aerodynamic coupe body for NASCAR competition, like Chevrolet's 1986 Monte Carlo SS Aerocoupe. 2+2-specific pieces are an aero nose, bubble rear glass and a fiberglass trunklid with integral spoiler. All 2+2 models came equipped with a corporate 305 cu in (5.0 L) four-barrel engine, the 200-4R four-speed automatic transmission and 3.08:1 rear axle ratio. They have a two-tone paint job with silver on top and gray on the bottom, with 2+2 decals and striping and 15x7 steel Rally II wheels. Modestly successful on superspeedways, where its bulbous rear end earned it a nickname of "the whale", the 2+2 design was seriously flawed for street use. Since the enormous rear glass was fixed (not an opening hatch), it forced adoption of a dramatically shortened trunk opening. Although it had modest horsepower, benign handling and design compromises, there were only approximately 1,225 Grand Prix 2+2s built in 1986 and all found buyers.
While the 3.8 L V6 remained standard for the regular Grand Prix, a fuel-injected 4.3 L Chevrolet 90° V6 was added to the option list for models other than the 2+2. This engine was available with a three-speed or a four-speed automatic transmission.
Source: Wikipedia, 2015