Brahma/port/amp/application questions

Ok, Im thinking of ditching my two 12W3's in a 1.65cf/sub enclosure and getting a single 12" Brahma. If I did, The brahma would most likely be going in a 3 CF ported enclosure tuned to 24 Hz. Would this sound ok? Also would it compare in output and SQ to my W3's? Right away I would be using my cadence Z9000 (800 watts x1 @ 4ohms) to run it until I could aford a A7HC or a bp1200.1 . Would this be enough to get some decent sound output from it? Also, I am relatively new to ports, and had some questions. If in WinIsd you change to multiple ports instead of one, the port length doubles. Is that total port length to be split among the two? Why does increasing the port size make the length longer? And how much port is needed? why is a larger port more benificial to a smaller port? I was thinking of something like 3"x6" or 2"x8" or something. any help would be great!!

this is a rough drawing of what I want to do . I have an Escort hatchback and the box would fill the whole trunk/hatch. The sub will be inverted(I COULD make the box bigger If I didnt want the sub inverted.... but I think 3 cubes is good) The orange things are my cadence amps on the back of my rear seats, and the round thing is the sub. tell me what you guys think.

 

thanks for the reply seth. IF I did go sealed(which I nearly always go with for the transient response) I would probably go with around 1.5-2CF(I love a good bessel response). I dunno.... modeling it up on WINISD gives a nice flat curve all the way to 25 Hz.... but Itll take up more room, be tougher to build, and weigh more in the hatch of my POS.

Do you think 700-800 watts would keep the brahma happy for awhile? Are you sure it will have the output capibility(SPL) of my 2 W3's?