From @Tob post #277 in the thread below https://trackmustangsonline.com/thr...our-gt350-or-s550-mustang-today.10476/page-14 Ford tested with upper grilles that had more total open surface area with respect to the intake tract. Here's a shot with a block off plate in place during cold weather testing. I'm not here to argue efficacy or necessity as the powerplant does pretty darn good with the rather restrictive inlet in place. When I had my front fascia off for front hook mount work I decided to open mine up a little. Here is the "funnel" in place behind the factory upper grille. With the grille block off plate removed and placed in front of the honeycomb portion, you can see how the majority of the funnel is blocked off, leaving a very small opening over to the right for air to flow through. Without the block off plate... I trimmed the plate with a few things in mind. I kept the new opening a little higher to avert clash between the newfound stream and the original one. You could argue that from an aesthetic perspective that it looks off and I wouldn't disagree. There is a slice taken out of the funnel on the lower left hand corner which precludes a more symmetrical opening that would be at the same elevations as the radiator opening or the original, small opening for the intake tract. I could have gone bigger but was concerned about a false air reading at the mass airflow sensor (which has proven to be a non-issue) as well as additional water intrusion during a heavy downpour at speed (another concern that was invalidated). You are a bit limited as to placement due to the upper fang location which splits the two openings.