If the measurements you gave on your current box is correct...it is tuned to ~49hz.
That is why you are getting little to no low-note reproduction.
Try that sub in 2.25cuft w/ a 36sq inch port 22" long. You will be MUCH happier w/ it.
I set my buddy up w/ a DD3512E in a similar box on a IA20.1 in his 06 civic si...it will stun ya //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
Handles the power fine too.