multiply your height, width and length of your port in inches and then divide it by 1728.

okay, that got me the cubic feet... I already knew my cubic feet, i was looking for the 80-90 in2 like you said. How much is 80-90 in2 in cubic feet.
85 in2 = how many cubic feet?

Port area doesn't come out to cubic feet. The port displacement does, but not port area. Port area is just the height multiplied by the width of the port. I would make your box out of 3/4" and have a double baffle on top. So if 18 is your height of your box then the port height would be 15 3/4" and then have the width 5.5" which is 86in2 of port area.

 

However your dimensions are way too small. You need more depth so the tuning will lower and the volume will go up.

Okay, thank you. Il try making a box like that then.

Yea no problem. You could make the width 5 1/4" if you want also.

Okay, so my new box

L= 36 in.

H= 18 in.

D = 20 in.

 

With a 5.25 x 15.75 port, I need over 50 inches of port length. That seems like its too much for a box of this size. If its right though I cant argue

Okay, I just made a model, the port being over 50 inches long takes away space needed for the subwoofers... this cant work in this size of a box. I will try to expand it later.

 

I am going to try to expand the box a little where I can. Could I possibly lower the port to 5 inches? I know its 78.75 instead of the 80-90. Im looking for good SQ as well as some SPL, I dont want to blow the doors off without sounding good.
 

Edited May 12, 201312 yr by Dangercdv

Port width can be 5"

 

You will need add to the depth.

Total box outside dimensions. 
H=18
W=36.5

D=22

 

And the port is 5 x 15.75 and 42 inches deep. This is tuned around 31.5hz and leaves room for the subs.
Thank you for the help

The subs will have just over 2 cubes each which is great and you have a lot of port area. You'll be happy with this box!

It is a little on the larger side for the recommended 1.5-2 for ported, but that's awesome. I think I will be happy with this

 

I hear that its best in an SUV to have the subs up, and port back. So this is what I got. look good?

Looks good! You should flush mount the subs. Also try to have them as close to the left side as possible.

Oh yeah, of course I will do my best to balance the sound. And I will try to flush mount. Thanks for the help.

Yea no problem. Post some pics when you get it built.