This is on my old Dakota. Her belly is quite messy, and with the layout of the drivetrain, both axles, t-case, exhaust and differing cross member heights, a belly pan would be somewhat difficult to pull off. I still may consider trying to fill the void on the opposite side of the truck, equal to the fuel tank, but that's not what this thread is about.
I've been driving it for most of the 16000 miles I have put on it, with a partially damaged front air dam. The previous owner must have tried to drive over something, idk. Needless to say, it was very filthy, from an aerodynamic standpoint, with exposed suspension, open frame rails, etc. I finally got that replaced, and am now toying with the idea of an air dam.
With the number of parts that hang below the bumper, the air dam would be quite tall (~6-7") to make it hang equally to the lowest points of the truck (differentials, front cross member). With this being my work truck, and occasionally needing to go offroad, I don't want to lose too much of my approach angle. Optimal placement of the dam would be equal to the factory one, but what if I place it further backward? Flat across from tire to tire would probably be bad since the air wouldn't naturally have a curve to follow. What if I place it between the factory dam and flat against the tires? I have included a link to an Imgur gallery with my thoughts, it's at the bottom of this post.
I already have material for the dam that will handle the resistance and the mounting hardware. I would need to find something the bridge the gap between the factory dam and the new one, to keep the deflected air from getting back into everything I am attempting to cover.
Would I be hindering my MPG, since any air going under the factory dam would now be dumped directly next to/in front of my tires, instead of having a chance to go over the pickup?
Click for pics!