[spacemanspif]

Sam Powell basically has come to the same conclusions I have from reading on this board.

Basically a full smooth belly pan is the best but takes a lot of time and material to build and I don't think its worth removing panels every time you want to jack the car up or change the oil.

Air dams aren't as good as belly pans but effectively eliminate the amount of air that can become turbulent under the car and induce drag. But just a dam on the front only blocks a certain amount of space behind it as air then enters the underside of the car behind the front wheel. Adding side skirts keeps most of the air from coming back under the car until behind the rear wheel.

Its kind of a game of numbers. Air dam scraping the ground keeps 80% of the air out that a non-dammed car would allow in and has a "shadow" of 4ft. By adding skirts you keep out another 80% (80% of the previous 80%) and increase the dam's "shadow" by the length between the tires. These numbers are for argument's sake only and have no science to support them.

So the dam does most of the work, the skirts help to maximize the effort and bring you ever so slightly closer to the benefit of a full belly pan. Dam and skirts will never be as good as a belly pan but when you weigh time, materials and maintenance hassles to the mix I think its the best compromise.

Like UltArc said though, depending on each car's underside, a dam will have varying degrees of benefits.

At least that is the way I understand it. Please speak up to tell me I am dumb when I start giving bad advice lol.