box design help

Hey everyone, got a question for anyone who can help

I currently run a slot port setup. I'm wanting to change the box design and raise the peak freq.

Right now, the car setup peaks at 43htz. Max spl is 149db.
Current box is 3.85cuft, port inside dia is 3X15X18.5.

My best guess(and believe me this is a guess), is to have the box size 3.0cuft, and shorten the port length up to 15X3X4.

Before I go nuts with the jigsaw, just lookin to see if this looks right to all you who have more experience at this than me.

car is a mits hatchback if that helps

Appreciate the help.

How much space do you have? (A.I. Width, height, depth in inches))? I can help you out by using google sketchup, and give you the measurements for the enclosure, also what will you be running for subs?