It's the pump right under the alternator. It's suppose to recycle the air from the cats or something. You can also do a search for a short belt and just bypass the pump. I'm not sure about how much of a savings there is in power.
the only benefit that i noticed from removing the smog pump was cleaning up the engine bay. removing it allows you to get rid of all of those lines running over the passenger side header. as long as you arent running cats, there is no need for any of that to be there.
I bought a UPR smog pump delete bracket, fit was perfect and I finally got that whining, good for nothing pump out. The power increase is not going to be noticable, if there is any power gained at all. However, getting rid of all of those anoying lines that run to the back of your heads and your mid-pipe are well worth removing it. The pulley from UPR has a polished finish and looks great installed.
its supposed to save you 7 lbs, 7 lbs off your front end never hurts in my book. just ordered mine yesterday from summit to go along with my pulleys im putting on this weekend. i get a really bad groan from my smog pump when i cut the car off, so it will definitely be nice to get rid of that.