This old site is maintained for historic and technical reasons -
You need to be very careful on this one You will want to
cut it so that the black color of the plastic is not visible. If you
cut it wrong, you will wind up with a jagged edge or worse... This
will allow cold air into the fender (where your airbox sucks air from).
Another modification that I performed is cutting some of the metal
inside the hole and then the plastic inside the wheel well. This allows
air to cool the brakes. Adding a vent tube would help force air onto
the brakes. Also, the hole will already be there if you decide to
add fog-lights in those locations.