The purpose of the JK air dam, (so named by Jeep), is to direct air under the front end.
In doing so, it reduces drag, and lowers the pressure in the engine bay.
Some people who have removed it have reported a slight decrease in gas mileage, and an increase in hood lift when trucks go by in the opposite direction.
The increased hood lift indicates an increase in pressure under the hood, which means there will be less air going through the grill and radiator. That won't be a problem until you are operating the Jeep at the upper limit of its cooling capacity. An automatic transmission is likely to be the first to suffer, especially with the pre-2012 JKs not running an aux cooler.
A metal skid plate under the bumper will do most of what the air dam was designed to do, plus give a lot more protection.
2008 Unlimited Rubicon Automatic
Last edited by ronjenx; 07-20-2015 at 08:46 AM.