[lunarhighway]

on my car (wich has the lightest engine available for the model) part of the top grill is backed of from the factory with a flimsy plastic insert that blocks of two rows of grill as well as the back of the opel logo wich would also allow quite some air in.

also the bottom grill wich consists of 2 openings has the bottom one blocked, although i can't see if it's part of the bumper molding or a separate piece.

anyway, for the top grill it's is almost a 50% block with a cheap looking plastic bit that snaps in place behind the grill.

although this might very well be the cheapest bit on the car, the fact opel cared enough to put it there should mean it would deliver a measurable improvement wich could be marketed as better economy and emission figures (the later became more strict around the time the car came out).

personally i think the difference, between grillblock vs no grillblock is far greater than between internet and external.

a smooth external block would be best, but in the real world i think an internal block might be easier to make without altering the looks of the car, and still be just as effective.