BIG monster box, wich one is better?

[Mrop]

I'm making a Monster -box for next year.

got one 18" and 3000w capable of pushing 147,88dB peak 144,2dB (33s average on 35Hz - 56Hz).

now when i got car big enough, i would like to try as big box as possible.

the box will be 77cm in heigth and 100cm width, and im planning of making it 123cm long, so it will be over 800litres.

but the question is, shoudl i make 4th order bandpass with 42cm x 42cm port, 100litres sealed 700litres vented.

or a regular reflex box with 800litres internal volume tuned into 40Hz

both are almost the same according to winISD, but i can't decide wich will be better tho.

the box is going to be so big that it will be considered as a wall, but i will make it so i can take it off the car when not cpmetiting.

[EBW]

Just remember the sub specs... most subs lose power handling capability when you raise the internal volume, what sub are you running

[Mrop]

autostudio reference unlimited 18"

http://www.autostudio.fi/autostudio-reference-unlimited-18-subwoofer.html

no parameters, yet these are brand new on the market.

[Mrop]

i'm planning also a 6th order bandpass with 400 litres box.

200 behind 200 infront.

that's twice the volume i got now.