As I sat through this stupifyingly incompetent movie, I amused myself (because there was other possible way to be amused while watching this movie) by thinking about why sequels so often completely miss the appeal of the original.

In this case, I was not a fan of the first movie, but even I can tell what made it popular: it had attitude to spare, a believable (in movie fantasy terms) outsider culture of street racers, and capably filmed action sequences. And it had car porn — the vehicles were as lovingly backlit and erotically charged as a Maxim cover model. This movie takes only the least interesting character from the first film, played by the vapid Paul Walker, and puts him into a dumb undercover story that feels like a rejected script for “Miami Vice.”

Walker plays Brian O’Connor, who walked away from his job as an undercover cop in LA at the end of the first film. Now he lives in Miami and races on the streets for money. When given a choice between being arrested or going undercover to get the goods on a sleazy bad guy, Brian agrees to pose as a driver, as long as he can team up with childhood pal Roman Pearce (R&B star Tyrese, the only actor in this mess who shows any presence or class). Yes, there’s some history the two of them have to work through, yes the bad guy (Cole Hauser, barely registering on screen) gives them a test run to prove themselves, yes, the other undercover cop is a gorgeous babe who may be so far undercover that she can’t be trusted, and yes, there are lots of chases, races, and what Roman refers to as “Dukes of Hazzard stunts.”

Talented writer/director John Singleton (“Boyz N the Hood,” “Shaft”) is really slumming here. This movie has some of the most numbingly inane dialogue I have heard in many months. For a story about people who are in love with machinery, it is also absurdly low-tech. In one completely idiotic scene, the bad guy tortures a policeman with a metal bucket, a huge rat, and a torch (you don’t want to know, believe me).

It also has many too many close-ups of feet slamming down on pedals, hands shifting gears, and eyes narrowing meaningfully in the rear-view mirror. The cars may be fast, but I am the one who is furious at having to sit through this dumb movie.

Parents should know that the movie has some strong language and a great deal of violence, including gunplay and torture. There are girls in skimpy clothes and sexual references.

Families who see this movie should talk about Brian’s conflicts in deciding which side he is on. They should also discuss the difficult choices faced by undercover operators, who must stand by or even assist while their subjects commit crimes.

Families who enjoy this movie will also enjoy the original and “Gone in 60 Seconds.”