Hi, My name is Steve and I live in Maine and I've been cooking lambs and pigs and such whole in the spit. This is Tradition in my culture. Anyway I have a question on air draw, I just recently built this roaster out of a 275 gal oil drum and my first job turned out fine I just wasn't happy with the cooking temp which was right around 210 and I'd like to be about 275-300. I have a 4 " exhaust pipe for the exhaust and opened some small 1/2" holes and maybe 8 sq inches on the left and right ends of the cooker. I have always used charcoal briquets 2 bags to the time. Is there a minimum inlet size or where does one find the math calculations ?