thats what jack's two hdc 15's were in (9 cf gross) 3.20 aprox. cubic feet net after subs and port that I designed but that was under the impression that it would fit in his trunk...but 2.50 should still work well after subs and port because the 83 scriocco we did with two hdc 12's was in 3.35 total cubes net aprox for both 12's after the port and subs and still hits the lows pretty good...what amp and power are you using