the sucking of the engine should change the way the air is flowing too right?
The engine would create a low pressure, which would promote more airflow thru the scoops. ON the SR-71 aircraft, at Mach 3 the engines pulled in so much air there was actually a vacuum in front of a large portion of the plane, so it went even faster.
Here's a boundary layer test: Tape pieces of knitting yarn on the hood in front of the scoops, with some yarn under one end of the tape, and several inches of free length sticking out beyond the tape. Lay the free ends pointing across the hood, IE not pointing at the scoops. Now drive the car at only 30 mph. Were the free ends drawn into the scoops?? IF yes, then the boundary layer was "thinnner" than the thickness of the yarn. If NO, then try it again at 50 mph. The yarn should surely be drawn into the scoops.
We need a little pressure manometer, or wind speed indicator to measure the velocity of the air entering the scoops. If there was an air cleaner box, the manometer would tell us the increase in pressure over atmospheric inside the box. The pressure increase combined with the "low" pressure created by the engine vaccum would improve performance.
Note that the Super Stock hoods on the early Cuda's and Dart's had very large air inlets. So really a large inlet is needed to make most use of the "ram" effect at low airspeeds (around 100 mph).
I'll try the knitting yarn test when I get my Challenger up and running. Might be next year though.