Originally Posted by DaveOmak
.... and then the S.W.A.G. came into play.....
At the end of the day, this is as good as it gets.
I've been meaning to develop some better tools for calculating Stack dimensions, but Dave's suggestions are on-point.
One thing you might consider is to sleeve your stack with a pipe of 4" x 8" rectangular (equivalent to 5.3" dia). This will give an equivalent volume of 668 cu-in. The insulating effect of the outer sleeve will improve the draw and make it less susceptible to outside temps.
As you can see, there are many ways to skin this cat. Don't worry too much about it. The stack will work as long as you are in the ballpark.
Edited by SmokeJumper - 7/29/13 at 10:20pm