I built a sub box as big as i could to hold two 18's in my acura cl.i run a 1200w hifonics brutus and it slams.But the speakers supostu have 6cft of air .the box only has 6.4 total inside air space. Is there any way to make the subs work easyer.By adding polyfill ,porting,or any other methed.i dont want to build a real intriqet box considering my trunk only holds about 13cft and my box should have 12cft.Any help would be appreciated.

You could drop to one 18" ported. You obviously don't have the room for two ported or sealed.