Tuning frequencie 12, and 15?

Im doing an install with 2 12"s and 2 15"'s  in one vehicle.   I tryed to talk the guy outa doing it, but he wants it.  So im going to run the 2 12"s at 50-80hz , and the 15" 50hz down.   I was just wondering what i should frequencie you guys reccomend porting the box's too?

IM useing 2 cerwin vegas, 12"...i don't know the model/     and 2 alpine r-15"s.  The r-15\"s are going to get about 3-4 cubes each,

Tune the port on the 15's to around 38-24 hz, it really does not matter too much here. Make sure that you have a subsonic filter on the 15's. I too would not mix these driver sizes, he will get much better results with 4 drivers of all the same size, especially if he steps up to better capabilty subs. It sounds like he just wants to get loud, I think he is on the wrong track, but if it's what he wants and will pay for, so be it.

A subsonic filter is a circuit that either comes on an amp or sound processor that eliminates lower frequencies that we can't hear from being reproduced, it helps protect your subs (especially in ported enclosures) and saves your amp from wasting a ton of power which makes the amp more efficient. They are usually adjustable and come on most new mid-range and up amps, especially class d's which are meant to push subs.