Sorry about all the questions, just getting into FI.
There are two possible taps for lines on the Raptor BOVs. I know that the boost signal line from the plenum goes to the upper port of the BOV. What is the lower port of the BOV used for? I looked at several pictures and cant see anyone else using it for anything. If you look at the picture you can see the port, but there is also another spot for one to the left of the one in the pic
thanks

 

It is there so you can hook up another boost reference line if you want for a bit better valve control. You don't have to use it and if you don't leave it open. Instructions for that are here: http://www.turboneticsownersclub.com/viewtopic.php?t=10

 

you wouldn't hook it up to a manifold vacuum source.....you'd hook it up to the pressure port on the scroll of the turbo. It would make opening response time even quicker. You would have to use it in conjuction with a normal manifold vacuum source hooked up to the top port, too.