Last year at the Geneva motor show, Alfa teased us with a 'prototype' 4C Spider. We wanted it. But we didn't want them to tinker with the recipe when trying to make it road legal.

Well, there's good news. The production version has just been revealed at the Detroit Motor Show, and the design has barely changed.

The obvious thing to note is the lack of lid. There's no complex retractable folding hard top here. At first the car will only be available with a soft, stowable canvas. However an optional carbon fibre hard-top will be available to the UK when sales begin later this year.

You'll also notice that the coupe's opinion-splitting 'moon crater' headlights have been replaced. Cleaner carbon fibre single lens options like were first seen on the 4C concept car now adorn the front, and the Spider looks a lot better for it.

Amazingly, the scalping hasn't hindered the chassis stiffness, or put on the pounds. Thanks to thinner glass in both the windscreen and side windows, plus a new carbon fibre windscreen frame bonded and bolted to its carbonfibre monocoque chassis, only 10kg has been added to the kerbweight.

Power comes from the same 237bhp mid-mounted turbocharged 1.7-litre four-cylinder engine used in the 4C coupe. And the same frustrating six-speed dual-clutch automatic gearbox is linked to it. But there is a new optional central exit lightweight Akrapovic exhaust. That should happily fill your ears with the dump valve's chumpfing and chirruping once you've gone to all that effort of peeling the roof off.

You'll be glad to hear the vital performance stats haven't changed, either. Alfa Romeo claims the 4C Spider is just as quick in the 0-60mph sprint as the coupe (4.1 seconds) and goes on to the same 160mph top speed.

Unfortunately there's no word on price, but expect it to be north of £45,000.