port size, 2 kicker cvr12's

You've been around this forum for awhile, so you know about the box volume and port calculator apps found over to the left side....

https://www.the12volt.com/caraudio/boxcalcs.asp

1.  Find the cubic feet volume of the chamber you wish to vent.  Use the box volume calc.

2.  Decide on square inches of port opening you want to use for your situation.  Then use the port length calc.  For purposes of using this particular calculator which asks for (round) port diameter, you can use the following as a guide:

4" Diameter port is 12.56 sq in.

5" D is 19.6 sq in.

6" D is 28.26 sq in.

7" D is 38.47 sq in.

8" D is 50.24 sq in.

3. Divide the square inch opening space by the longest side of the port that you would like to use (or are limited to), and the answer will be the other dimension of the opening.  Example:  28.25 sq in opening space / 12" (example of a limitation of inside box height) = 2.35".  Which is to say, a vent opening that is 12" X 2.35" = 28.25 square inches.

For your two subs at rated power input (and with regard to box volume and Fb), the port opening should be no less than 28 sq in, and preferably in the area of 35 to 40 sq in.  If the opening is too small there will be port noise interference.

For double-checking your work, here's one calculator you can also try:  http://www.subwoofertools.com/forum/portlength.htm

You should be aware, though, that CompVR's will perform best in large sealed boxes, not vented.  Re:  http://www.kicker.com/06/tech-support/manuals/manuals/2007/2007%20CompVR%20Sub%20c01%20Web.pdf

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.