kicker comp 12

Im building a box for 2 12" kicker comps single 4 ohm coil. I called kicker and they told me to build a 2.1 cubic ft box per woofer. I then checked on the website and it rocomends 3 cubs per sub but i already had the wood cut to build a 4.2 cubi ft box (2.1) per woofer.. So the box i have is 2.1 cuic ft per woofer. Next they told me to use a 30" square opening per sub 20 1/2" long. To me that seems like to big of port per sub but maybe im wrong.. Wondering if anyone knows what slot port will work best for theese woofers?? So what im asking is the 30" square opening a good choice to use or does someone know what size port will work the best for theese woofers ?? I wanna use slot ports and the box is at 2.1 cubic ft per woofer right now.. Any help would gretly be appericated

You've asked a sort of mess-of-a-question here.  First, if Kicker recommends 3cf per sub for a ported enclosure, then that's what you should have done...messing around with the airspace (especially by 1/3) can have a big impact on the SPL and/or SQ of the sub.  As far as port length goes, the port length is going to be contingent on the tuning frequency of the sub which should be on the spec sheet (or you can contact kicker) BUT you're going to have issues since the tuning freq they recommend is based on the assumption that you are building the enclosure with the appropriate amount of airspace.

  A 20" hole is GIGANTIC for a 12" sub...that simply cannot be right.  My advice would be to wait til you get the sub before cutting the hole.  As far as the port goes...well, I guess just find out what the tuning frequency is and use that as the basis for port length BUT my overall advice is to rebuild the enclosure to spec or simplify and just build a sealed enclosure.

Not a 30" square opening, but a 30 Sqare inch opening.  3" X 10"  or 5" X 6" opening.