air intake/front grills

An air entrance on the front grill isn't going to do much in the way of improving airflow to a filter, if anything.
High velocity low pressure air at the entrance will become turbulent around the edge and therefore reduce flow. Having a diffuser on the lower edge of the front bumper ala btcc cars will help though can be quite impractical on a road car.

THE best place for an air feed is the scuttle area, as this has the highest pressure differential.