The custom 1950 Mercury driven by Cobretti in the film was a car actually owned by star Sylvester Stallone. The studio produced stunt doubles of the car for use in some of the action sequences, such as the jump from the second floor of the parking garage.
When Sylvester Stallone was signed to play the lead in Beverly Hills Cop (1984), he did a lot of work on the screenplay, turning it into an action extravaganza that the studio couldn't afford. He eventually left Beverly Hills Cop and channeled his ideas for that project into this movie.
Most 80s action heroes were called John (John Rambo, John Matrix, John McClane etc.). However, in this movie the hero is named Marion, which is the real first name of the epitome of the cinematic tough-guy - John Wayne.
Original rough cut of the movie was over 2 hours long. Due to the concern that it wouldn't be a hit,it was cut down to 84 minutes. Some of the deleted material was cut because of the MPAA,who originally gave the movie an X rating due to the graphic violence. After massive re-editing,great deal of plot was either removed or speed up,while most of the violence and nearly every death scene is edited or is always happening offscreen,often causing many continuity mistakes. Because of the re-editing,a great deal of action scenes is also cut.
A very rare workprint of the movie is available amongst fans. Although most of the copies of it are in poor quality,it has approximately 30 or 40 minutes of extra scenes which are not available in any other version. It also has all of the X rated material removed from released version.
The submachine gun used by Marion Cobretti in the final showdown with biker gang is a Jati-Matic. The Jati-Matic first appeared in the early 1980s, but was never adopted by any country for use. It re-appeared in Finland in the mid-1990s as the GG-95 Personal Defense Weapon made by the Golden Gun Company. The gun is chambered in 9x19 parabellum, has a cyclic rate of 600 rounds/min, and has various accessories that were offered such as a silencer, various capacity magazines, and a laser pointing device.
Andrew Robinson (Det. Monte) and Reni Santori (Sgt. Gonzales) had worked together 15 years before in another cop film, Dirty Harry. In that one, Robinson was credited as Andy Robinson, who played the psychopathic 'Scorpio'.
Cobretti uses a custom Colt Gold Cup National Match 1911 in 9mm using Glaser Safety Slugs, a frangible bullet. This is shown when he unloads his pistol in his apartment to clean it. The Colt Gold Cup National Match 1911 is usually chambered in .45 ACP, the 9mm versions were made especially for the film.
The Paula Gosling novel 'Fair Game' on which "Cobra" is based is also called 'A Running Duck'. When the movie came out Sylvester Stallone allegedly wanted the novel reissued with himself credited as the author. Ms. Gosling declined the offer.