High speed stability issues

Not so much a pan, but an air dam. upload_2021-7-9_11-46-1.jpeg

maybe a bit bigger, though that might be enough & at those speeds the force trying to rip it off go up exponentially
I am by no means an aero expert, but I did stay at a Holiday Inn once. Maybe some others will chime in.
By pushing air around the car, it also works the same way as what I was saying about up top, it creates a vacuum zone under the car, also sucking the air through the radiator & out of engine compartment, taking heat with it.
PS, someone else’s beautiful Dart-not mine