And then some. The first film grossed more than US$200 million worldwide, spawning a franchise that supplies Universal Pictures with the kind of adrenaline (not to mention cash) that studios live by these days. By building on the film's multicultural base to help market it globally and amping up the spectacle and stunts, the franchise just keeps getting bigger.

Last weekend, raced to No1 in the US with a massive US$143.6 million domestic opening. If early estimates hold, the film will mark the biggest debut for the franchise, which has so far racked up more than US$2 billion worldwide. It would also become the ninth-biggest debut in box-office history.

"The first film was made as sort of a counterculture, midrange-budgeted action film with a definitive concept at the centre of it," says Donna Langley, Universal's chairwoman. "Over the years, we've been able to grow the franchise creatively to make it global. A little bit of timing and a lot of strategy has worked in our favour."

Even the franchise's creators admit that initially the series was largely about hot cars and hot girls and guys. The stunts have grown increasingly outlandish - at one point in the crew drives cars out of a plane and parachutes onto a mountain road - but filmmakers have attempted to play up the series' emphasis on family.

The multi-ethnic cast is tightknit on and off screen. Some of the stars, such as Jordana Brewster and Tyrese Gibson, rarely even act in movies outside the franchise. The cast's bond deepened when Walker - often referred to as Diesel's brother - was killed in a car accident in late 2013. (The actor's death occurred midway through production on , so he appears in the new film although some of his scenes were completed with the aid of special effects.)

While bigger names have been added to the franchise over time - Jason Statham and Kurt Russell have roles in - its core has remained intact, a rarity for a multi-year project. By contrast the "James Bond" franchise has swapped out the actors for the title role multiple times. Other modern franchise films and characters such as Batman and Spider-Man have changed casts and concepts frequently.

"We look at the franchise much like a TV series where we've created characters that the audience has become connected to and familiar with," Langley says.

New directors have been brought in for different instalments, bringing fresh energy and sensibilities to the franchise. James Wan, director of , comes from the world of low-budget horror flicks.

The action in the most recent films takes place around the globe. goes from London to Los Angeles, Tokyo, the Dominican Republic, Abu Dhabi and back to Los Angeles. In fact, it was the franchise's migration out of the US with 2006's that got it back on track.

At the time, Universal was considering releasing the third instalment straight to video because Diesel and Walker were not a part of it. That was when screenwriter Chris Morgan responded to an open call and pitched studio executives on moving the series to Tokyo.

"I told them I thought DVD was the wrong way to do it. I didn't want to be known as the guy who was the franchise's killer," Morgan recalls.

" They wanted to set the film in high school, and I started spitballing my idea about going global. Yes, that provides exotic locations and interesting set pieces, but I think it works because the crew represents something that is about acceptance - it doesn't matter where you are or what you do."

Of course, it also helped that Diesel and Walker returned for the fourth film in 2009. "[Universal] kept the core family of cast but infused some new blood in there, almost like guest stars on old TV shows," says Paul Dergarabedian, a senior media analyst at research firm Rentrak. "They also amped up the action … it became more than just a fast cars, hot girls, good-looking guys kind of movie."

The franchise was on a roll until Walker's unexpected death, which caused the studio to question whether to scrap one of its most lucrative properties.

"We were like 'OK, we're done. We had a good run,'" Moritz recalls. "We didn't know how - emotionally - we could finish this movie without Paul. But the studio let us grieve and try to figure out what the right thing to do for him would be."

Langley says "the first 24 hours after [Walker's death] were critical" because that time helped establish how the studio was going to move forward.

"Our job was to do it in the most respectful way and create a legacy for him that he would be proud of," she says. "That was the sentiment and the thing that carried everybody through from that moment until … we finally finished the film."

The release date was shifted from summer 2014 to accommodate the delay. Caleb and Cody Walker, Paul's brothers, were brought in as stand-ins. Computer effects were used for facial replacement to complete Walker's scenes.

"Cody and Caleb have mannerisms like Paul," director Wan says. "They moved like Paul, talked like Paul - in a lot of ways it gave the actors closure. I think that was the right thing to do for all of us."

Morgan also decided to leave Walker's dangerous action scenes intact - even if they called to mind the way in which the actor died. "To not have [Walker's character] Brian in situations that Brian would be in would call more attention to it," the writer says.

"The joy and surprise is if you didn't know that Paul Walker had passed away, you'd have no idea while watching this - and that's the point. The movie feels genuine and fun, and I don't think you really dwell on his death."

Universal doesn't expect the franchise fandom to end soon. "I think there's a lot of gas left in the tank still," Langley says.

Fast & Furious 7