Help with aero port Enclosure build.

[Shokaz]

Haven't really done any kind of audio build in the last couple of cars I've owned so it's been some years and I'm starting to get the itch again. I've built slot port boxes before but never tried an Aero port type ported enclosure. Looking for a little help on port size and length. I'm going to do 2 Audiopipe txx-bdc4 15's. I have measurements from my Jeep and have a rectangle box that ends up being 7.1 cubic feet after sub displacement.

 

I'm looking to tune around 31hz. Anyone have some insight on port length and size that I should be going for? Aero ports are 100% new to me, I just never looked into them. So I'm not sure if (2) 4" ports or (1) 6" port or what I should be going for and what length. Help would be appreciated from some of you experts.