It’s debatable what’s more appealing in “Racer and the Jailbird”: The sleek Porsche 911s or the two knockout actors behind the wheel. No offense to hunky Matthias Schoenaerts and pouty-lipped Adele Exarchopoulos, but I’m going with the car. The Porsches are sexy, shapely and (especially on a movie critic salary) utterly unobtainable. But a guy can dream. And all of mine revolve around the sapphire-colored Carrera (price tag $95,000) steered by Exarchopoulos’ speedster, Bibi. As Tom Cruise so reverently quipped in “Risky Business”: “Porsche. There is no substitute.”

I wish I could say the same about this discombobulated mess of a movie from Belgium writer-director Michael R. Roskam, best known around these parts for his adaptation of local hero Dennis Lehane’s novel, “The Drop.” Like that cult fave, Roskam is once again transfixed by dogs and the lawbreakers who confront them. He’s even cast “The Drop’s” Schoenaerts in the lead, playing a Belgium bank robber whose kryptonite is kynophobia. That’s a fear of dogs, in case you’re wondering.

No worries because the woman his Gigi is floored by is Exarchopoulos’ race-car driver, Bibi — and believe me, she’s no dog. In fact, she might be the most beautiful woman to ever slip on (and off) a racing suit. Good thing those zip-ups are fire proof because Bibi is so smoking hot she could make tungsten boil. Understandably, Gigi is smitten from the get-go, and there’s no turning back. For Bibi, the feeling is mutual. And that should be the end of the story. Unfortunately, there’s still another 115 minutes to go in a movie that at times seems longer than the 24 hours of Le Mans.

That’s because Roskam is really into making Bibi and Gigi (Don’t you just loathe those cutesy names?) polar opposites who attract. She’s rich, refined and naive; he’s poor, boorish and streetwise. And, as I mentioned, he likes to pull elaborate heists with the blue-collar gang he’s been buddies with since childhood. So let the lessons begin in contrasting how life treats the stinking rich Bibi and the larcenous Gigi so differently. There are even hints of Jack and Rose from “Titanic,” when Gigi treats Bibi to a fun, raucous night of dancing and partying in a steerage-like juke joint. Who knew blue-collar types were so fun?

But don’t let my cynicism fool you. For the first hour, “Racer and the Jailbird” is actually pretty solid, drawing on the nice chemistry between the two leads and the juxtaposition of their diverse worlds inside the city of Brussels. Even the sex and nudity is good, albeit gratuitous. And like I said, there’s those Porsches: One souped-up model for Bibi to pilot on the track and another street version to drive for her high-speed pleasure — until the intolerant Brussels cops pull her over.

Then Roskam takes a few corners too fast and drives his movie straight into a wall fortified by steel-reinforced clichés and rock-hard melodrama. There’s jail, there’s cancer, there’s a prison break and there’s a marriage proposal. Oh, yes, and what would a story like this be without — let’s say it all together — “one last heist.” What could go wrong? Well, in addition to the movie, quite a lot. But I don’t want to spoil it; Roskam does a good enough job of that on his own. Suffice it to say, the odds of a happy ending are evaporating fast. And what do you want to bet Gigi will eventually end up face to face with a snarling dog that is just like him: Abused, mistreated and shunned by polite society?

At least the film looks great, as Roskam makes excellent use of locations in his native land, including the infamous Circuit Zolder, where Formula 1 legend Gilles Villeneuve met his demise in 1982 while qualifying for the Belgium Grand Prix. And director of photography Nicolas Karakatsanis does a fine job of using light and shadows to contrast Bibi’s life of luxury with Gigi’s dank past, present and future.

Kudos also go to Roskam for casting Exarchopoulos, who has been conspicuously absent from the international scene since taking the world by storm with her Cannes-winning portrayal of a teenage lesbian in the exceptional “Blue Is the Warmest Color.” She again works her magic, even though she is often failed via a script by Roskam and two other writers that cloyingly make unearned plays upon our emotions. We’re never given any reason to feel. Perhaps that’s why you care more for the inanimate 911 Carrera — praying it will never crash — than you do the horndog lovebirds occupying its two front seats. Like Jared, they’re expendable; but like Ivanka, the Porsche is where we draw the line. It’s too beautiful to let anything bad happen. Like we said, there is no substitute.

“Racer and the Jailbird”
Cast includes Matthias Schoenaerts, Adele Exarchopoulos and Eric De Staercke.
(R for some strong sexuality, nudity, violence and for language.)
Grade: B-