Porting a sub box is more than just drilling a hole in a box. Alot of things take into affect the port size and length.
I am sure Richiec777 and 2muchricemakesmesick will pop in and give some advice also.
The port depends on what frequency you want to play the sub at, and if the enclosure is big enough to produce it.
Being that you have a JL box, I know they are pretty small. Usually ported sub boxes require more air space than sealed boxes.