From
Wikipedia a flat plate perpendicular to the flow will have a Cd of 1.98-2.05. However if we extrapolate the dissertation to a mesh with 0% open area the Cd will be significantly higher. I think the two test situations are different enough that the results do not directly translate.
I think the Cd changes if air can flow around the obstruction rather than just being stopped by it.
With a stock grill the issue is the radiator shroud, the engine and the engine bay acting like a blockage. Where as the solid grill block directs the air around the blockage giving us our MPG gain.
Here, California98Civic says,
Quote:
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Drag is important, and it is our normal obsession. But I would trade marginal drag increases in my grille blocks if it meant significantly reduced radiator-fan run times.
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I think he is talking about the low speed benefit of mesh letting air flow through as opposed to his current solid grill block. So he would like something that has worse drag as long as when he was stuck in traffic he could draw more air and cool faster, which is what is being theorized about using mesh instead of a solid piece.