There are a multitude of sweet looking motor gubbins that make passers by lower their chin and nod slowly. The rear roof lights on a Citroen DS; the "floating arches" on a Ferrari 599; the "Coca-Cola kink" on a '69 Dodge Charger to name but a few. And of course, nay as always, the NACA Air Duct. I was reminded of these things when I saw the roof of Bugatti's Super Sport (see below) and got me thinking to why one sees so few of them on our roads. The last time I saw those on a car they were on the hood of the Ferrari F40. I like NACA ducts, they'll look forever cool because their purposeful look is always backed up with, well, purpose. Case in point with the Veyron. So what do they actually do? I'm not an expert on this but the general gist is they're used to simply cool down the cabin of a car with minimal disturbance to the air flow passing over a car's body. Put it another way, if you've ever tried to cool down on the motorway by opening a window you may have noticed how the rear window suddenly acts as a parachute, slowing the car down. So why not used air-con? Well if you're going to build an uber fast car sometimes air-con is considered to be unnecessary extra weight. Hence why it appears on the feather light F40. Check out the Sauber Le Mans Car pictured for a large example. So the reason we don't we see NACA ducts on our roads is that they're simply not needed. Most cars have air con or the traditional "roll down the window for a breeze" device. Although they may be rare you are reassured that when you do spot one that the machine it's carved into ought to be quite special indeed.