Hello. I've got a ported 5.3 cu.ft box and 1.6k amp (my box is 1.1 cf ports and 4.2 cf for the sub) which sub would be better with my setup? the Z v3 15" or the 18" ? also I've got XS power D2400 battery. I cant get a bigger box, thats the maximum box size that I can have. is my mono will be enough for that sub? (can't change it, I'm out of budget) is that box is enough for the 18" ? if not, is it good for the 15" or is it too big? * car details: I have a Fiat Grande Punto (small car. hatchback) and my box is slanted front if it matters. Amp: Celestra FA1.6k Thanks, Udi.