This is how i did my 745 BMW Cake. Not all steps are included in the picture, but you can get the idea. To create the shine. I just painted it with black food coloring and clear vanilla.
A CAR MECHANIC CAKE in the making - The brief was to have a mechanic working on a VW golf with the bonnet open. The car is a shaped madeira sponge cake as a cake topper which was placed on top along with a mechanic and car jack.