NASCAR Racing: nascar race cars, air regulators, race cars

Question
Why do they use tape on the nose of the car to regulate air flow to the engine?.  Why don't they have some kind of automatic regulator that opens and closes to change the air flow?

Answer
They use tape to cut off the airflow underneath the nose of the car. When air gets under the nose of the car, it makes the car tight, so they block off the airflow so the air will flow over the car and not under it. I really don't know why they don't use air regulators. I'm guessing it would just be too complicated.