A tale of two drums

[T G]

I just finished my second drum a couple of weeks ago, doing 3-4 meats for competition is a massive pain one one drum. My original drum likes to run about 265-270, and I have no problem with that. Its 23" dia x 40" tall, and I have a 4" tall stack on the lid. This second drum is 2" wider in diameter, about 4" shorter, and I didnt put a stack on it. That particular drum doesnt like to run much above 230. Thats great for when Im cooking ribs, but bad for chicken and if Im trying to cook a brisket in 8 hours. The first comp I used the new drum it sat at 230 for 11 hours with very little charcoal consumption. But if I try to run it at 250-260, it will throw a screaming hissy fit and fight me the entire time. Not to mention it will run through a 20# basket of coal in about 5 hours. I have to open all my intakes and crack the lid open to get enough draft to run hotter like that.

Knowing what I know about drafts, Im thinking that having the shorter wider drum and no stack isnt getting enough of a draft to stoke that fire properly. Im also wondering if more air is bypassing the fire basket than actually entering it due to the wider diameter.

Im thinking I need to extend my intakes to right at my fire basket and add a stack, to promote more of a draft and get more air into the fire. Does that sound like the right course of action?

 

[T G]

bumping....anyone?

 

[UDSPowercat]

I'm just guessing, if it were me, I would try a larger diameter exhaust stack.

 

[Salmonsmoker]

TG,
I'm not convinced that needing an exhaust stack to create draft is the problem. If you have to completely open all of the intakes and then crack the lid, that tells me your exhaust is restricted. Does the total square inches of your exhaust match the total square inches of your intake? I don't think the barrel size is an issue either. Air entering the drum isn't going to bypass the fire basket or the fire would die out. The fire is going to to take the air that it's given and burn all that it can with that given amount of air. There's plenty of heat to create draft, but if the flow is backed up to the point where the fire can't draw, or only allows enough draft for the fire to maintain 230F that tells me you need a larger diameter exhaust. I have the BPS drum kit. It has 8 - 3/4" holes of intake at the bottom of the drum and 8 - 3/4" hole for exhaust in the lid. Intake = Exhaust. There's no stack, just a daisy wheel draft controller if I want to use it to help control the air flow. It's always wide open except when I close all vents to shut down after a cook. Hope this helps getting your problem solved and get that drum cooking like it should.
Cheers!

 

[T G]

Holy crap that makes perfect sense, I was just overthinking it.

Im running 3x 1" ball valves, and using the 2" bung that the lid came with. I need to cut at least another 1" exhaust in the lid.

Thats one of those "it's so obvious I feel like an idiot for not seeing it" answers, thank you.

 

[BabelBBQ]

Cutting that hole would make your high school geometry teacher cry. Might fix the problem, might not. If it does it won't be because of intake=exhaust. An assumption I'm making, 2" bung and 1" intake are each the diameter not radius. So the bung has a radius of one inch. (A = pi*r^2) exhaust area is pi*1^2, or about 3.14 square inches. Each intake has a radius of 1/2, so each intake has an area of pi*(1/2)^2=pi*(1/4). You have three intakes for a total of pi*(3/4) or about 2.36 square inches. You have less intake than exhaust. If intake=exhaust is the magic equation, then you need more intake (exactly one more one inch intake gives you another pi*(1/4) square inches for a total of pi*(4/4) = pi*1 or about 3.14 square inches.

I know it is counter intuitive that a two inch whole doesn't have twice the area of a one inch whole, it doesn't it had four times the area. Ratio of areas of similar figures = (ratio of the corresponding parts)^2.

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[BabelBBQ]

Hole not whole.

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[BabelBBQ]

Here is a visual showing that the 2 inch bung has a larger area than 2 one inch intakes.

Believe it or not the open space above the two small circles and inside the big circle is equal to the area of one of the small circles.

 

[Salmonsmoker]

TG, you hadn't given the size of your intakes when I posted earlier. My calcs match Babel's. Hmm..............