Well, the firebox should've been about a 24" cube (according to the calculators); this one is 26" cubed. It is a bit bigger than called for, but it won't have a negative impact on performance.
EDIT: the recommendations say the firebox should be 1/3 of the chamber. If you think about it, our chamber is 72" long and 28" in diameter. The 26" cubed box is more or less 1/3. If it's bigger, it's a mundane amount. It's about perfect..basically rounded up.
This is a Jambo clone..which is why the bottom of the hole was cut at about the "equator". If you have the chance to look inside a Jambo (some of the Jambo owners may be able to lend a hand here), you'll notice that this hole is above the main level grate (which is about halfway up the chamber). There is a baffle of sort directing the heat. The position of the smokestack will draw the heat back down by the time it reaches the far end of the chamber creating an arch. This arch will be somewhat minimal, which helps to eliminate the hot spots across the chamber. It's "unorthodox" but it seems to work well. The smokestack outlet will basically be flush with the main level grate also (the bottom of this opening will start about 1.5-2" below the main level).
The placements of the inlets/outlets are virtually identical to that of the Jambo. From what I have seen, our firebox is actually insulated just a tad bit better, too.
Last edited by ThatsWhatSheSaidBBQ; 03-18-2012 at 12:03 AM..