I read an article in my 4wd mag where thay tested a performance throttle body. In the end it said since the vacumn had dropped they knew more air was getting into the engine. They also noted a power increae of about 5hp. I have vacumn gauges in my truck and my mustang. The one in my stang actually has markers on it indicating Bad, Good, better, Deceleration for MPG. But the way it reads, the more vac. you pull, the better mileage you are getting. Is that how it works, less vac/more power and more vac./better MPG? I just installed a CAI on my truck and noticed it caused my vac gauge to drop a notch. Just trying to figure out exactly what I have done. Feel free to correct anything I said, as I'm trying to learn a little here.