[lunarhighway]

you'r airdam looks a little 80's to me, makes the car look a bit like a bmw from that period form a distance...
however i think it could be better aerodynamically when you lengthen it a the sides to warp around the bumper all the way to the wheels... sinde ther's going to be a low pressure behind the dam those gaps in front of the wheel might actually suck in air...

On the other hand you might actually want to raise the airdam slightly in the middle... especially when you're considdering an undertray... although this had been used before it's an often sited feature of the calibra with a 0.26 Cd but a lot of curent cars roughly have this form.
ideally the raised portion in the middle would make a smooth curved transition to the undertay to prevent flow separation... if there's no undertray a ridge about an inch high is what most cars with that configuration seem to have.

the idea is that since you can't get the dam all the way to the road to get an airtight fit some air wich hits the car in the middle on the dam, has little alternative but to go underneath the car anyway, and the dam will just make that even harder to do, and even is part of this air is still be forced around the car this is also an engergy robbing process wich at some point may be worse than going underneath, even with a rough underside there.

on the other hand the front wheels and wheelwells generally seem to be regarded as potential high drag places and most cars have some sort of device to direct the air away from them, confusingly some cars than have holes or ducts added to provide some air to the brakes for cooling, but these don't help to reduce drag.