I was wondering if 11.25 net tuned to 31hz and 166.25 square inches of port is too much for 4 fully loaded  12 inch BL subs running off of 6,000 watts of power?

Post dimensions so I can see what u working with.

I have 48" of width, 36" of depth and 29" of height to work with. I can go more on depth if needed.

If my math is right your at about 14.75 or so square inches of port per cubic foot. So it's not too much, I think not enough. I'm thinking about 11 cubes with around 175-180 sq inches of port.

Wow so that much port is needed?

There is no relation between the vent cross-sectional area and enclosure volume.

What do you mean?

Don't compare vent area to box volume.  There isn't a relation or "rule of thumb"