[browney]

Ahh, O.K thanks! Now I get it!!!

Does the acceleration at the apex give a net downforce on the car if you look at the diffuser as a whole or is the effect there to help speed up the flow under the body of as a whole.

Thank you so much for explaining this to me. I asked my Aero lecturer but his explanation wasn't clear. He spoke more about the diffuser getting the boundry layer away from the ground so as not to choke the flow.