Put this in google -- ported box software

Now, you will need multiple specs for your subwoofers to figure out the correct box size and port diameters/length.

Also, other calculations like the resonant frequency of the vehicle you are putting these in and numerous other issues. Seriously, fixya.com is the wrong place to get this answered. Teams spends tens of thousands of dollars and years perfecting their vehicles to compete. Go to a good audio forum and ask this question there. You will receive ALOT better help and you can interact with some very knowledgeable people about your competition wishes. Good luck and have patience!!