Casper as you probably know is a race car but I also use it for my commute a few days a week. I am thinking about adding a splitter at the bottom of the airdam. the theory is it will force the air to go either over or under the car and reduce the amount piling up against the front of the car. I have looked at this for some time, what I've seen is a splitter is good for more straight away speed and better cornering. that sounds pretty good to me.
What little I read on splitters stated they create downforce. The effect pushing the air over the car also pushes down on the splitter. That will improve cornering, but will also increase rolling resistance.
an extended airdam probably does the same thing and I already have that. Hmmmmm...
I don't see how. An airdam is a flat verticle surface, and a splitter is lip at the bottom of that surface. When the flat verticle surface is moving, it pushes the air in front of it. The air pushes back. It just doesn't push back, it pushes in all directions with an equal force. So it is what is pushing the rest of the air over and around the moving surface.
Some will be pushed under, but an extended airdam will limit that. If there is a splitter at the bottom of the airdam, the downward pushing will push on it, creating downforce on the front of the car. A jutting front bumper under a flat grill does act as a splitter. It's why early 80's BMW's look the way they do.
The down force increases traction there and allows for better cornering. It will also increase rolling resistance. Depending on size of the splitter, and average daily speeds, it may have little effect on fuel economy. Any effect on economy will negative though.