well 1st off you wont find any pipe fittings that will fit flared ports. unless you make your own ports. two 4" flared ports will not be the same as 1 8". it would be closer to one 6". my box is 5 cubes with two 6" flared ports. now i know you want to be loud so i would go bigger than those two 4" ports. maybe 4 of them. i hear the larger ports work better but ive never done testing. look at psp-inc.com, they have a very simple calculator for their ports.