I forgot to add a few things up top...... research "Fluid Dynamics"...... also here is a good site.
http://www.strangeholiday.com/oops/stuff/annurev.fluid.38.050304.092016.pdf
From the research I have done, silverbullet1986 and a few others explain really well how Wind Splitters work. Here’s a little additional information you made need for know in regards to the flow of air under your car.
Please note I am that leaving some things out of this due to people already...