85/2640 * 3600 = 115.9cu'
If you write to Faber and demonstrate to their satisfaction how you'll use the information in their data base and drawings website, they'll grant you access to that website. It takes them about 6 months to get back to you regarding your request.
When you do that however, you'll be able to learn all kinds of interesting things like the specs on Faber's tanks - in this case the Faber LP "85s"
Per their own database, which is far more reliable than Faber's marketing literature, the shorter 7.24" diameter Faber LP 85 has an internal volume of 787 cubic inches and the taller and skinnier 7.01" diameter Faber LP 85 has an internal volume of 793 cubic inches.
The standard pressure at 1 atmosphere at sea level is 14.695 psi, so that volume lets us calculate the tank's capacity at it's full rated capacity (2400 plus the 10% overfill on a 3AA tank). So,
2640 psi/14.7 psi =179.59,
787 cubic inches * 179.59 = 141,338 cubic inches
convert that to cubic feet by dividing 141,338 by 1728 (12x12x12) and you get 81.79 cu ft.
Now we can calculate the volume at a cave fill of 3600 psi.
81.8/2640=.03098,
.03098 * 3600 = 111.54
Even if you re-run the numbers using 1 bar (14.5 psi) you still only get 82.9 cu ft.
The 7.01" diameter Faber LP 85 has an internal volume of 793 cubic inches. Crunch the same formula and you get 82.42 cubic feet at 2640 psi and 112.38 cu ft at 3600 psi.
The bad news is that your Faber "LP 85s" are really "LP 82s". Sorry.
The good news is that your SAC just improved slightly.