The factory box is a cold air kit - remove the silencer and put in a K&N - works just as well as cold air kits on mildly modded motors. Check out the test -- http://www.fordmuscle.com/archives/2002/03/coldair/ The u/d's will add a few HP - dyno tests show it over and over. However, there are potential side effects, and the gains occur largely above 3500 rpm out of the range of most street driving.
You want to do something that will make a difference for about $100? Send that lower manifold off to tmoss and let him port it. It's the biggest restriction on the stock motor, and port job by someone who knows what they're doing (requires welding on the intake) makes a noticeably hp/torque difference throughout the rpm range without affecting drivability.
You want to do something that will make a difference for about $100? Send that lower manifold off to tmoss and let him port it. It's the biggest restriction on the stock motor, and port job by someone who knows what they're doing (requires welding on the intake) makes a noticeably hp/torque difference throughout the rpm range without affecting drivability.