I don't reckon that grille is big enough, I would just put load of approx 20mm holes in it and leave it at that
I remember autospeed adding a vent to the wheel arch, it did F all. Reason being was the vent design was not efficient enough in improving air flow and it had no effect on the pressure under the arch which is what they where testing and measuring in the experiment, instead they decided to use a FMIC do to a bigger access of inlet air flow on a pd engine which are far more on boost than our engines, have a read:http://www.autospeed.com/A_108646/cms/article.htmlhttp://www.autospeed.com/cms/A_112259/article.html