box volume

I've been running 3cuft per speaker in my car.
I've got room to expand up to 4.7 per speaker (running 15's)

I'm trying to tune for 55 htz, but not having much luck.
Last build was 3cuft per speaker, with a slot port 3X15X4.

Last figure that I had for my new build, was a 4.7 cuft box, with a -1.4 port(round 4").

Would it be better to go smaller on the box size? 4.7 seems pretty big.

Thanks

Smaller will forsure help with the note

i run in 1.5-2 foot per 15 with 3.5-4.5"wide x 15 tall port per 15
a hole bunch smaller box with a bunch more port

'I'm going to try by starting with a 2' box, with 1 areo port, 4 wide by 8 long, for each sub-we'll see how it works