It's an air dam, and nice looking too. Although wider would do more, it ought to increase air flow through the radiator as it will help create a low pressure zone under the engine. Also, as an additional result of the low pressure area, the front of the car will stick better at speed. The somewhat crude and wider one I built for Woodstock gave noticeable benefits at over 60 mph.
As tested on the roundabouts of East Kilbride... (Not something to be recommended).
