How do car diffusers work? Why is a diffuser efficient? Diffusers play a big role in creating efficient downforce with low drag. Diffusers allow low pressure fast moving air under the car to expand and slow down, gradually rejoining atmospheric pressure with a large amount of turbulence and drag. This video explains how with visual demonstrations as well.
Diffusers - http://youtu.be/3DIJMLrGz8Q
Race Car Aero - https://youtu.be/QA6AtmX20pI
Ferrari/Williams Engineer Demo - https://youtu.be/DVHR8_B7bfg