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Q-talk *ON TOPIC ONLY* QUALITY ON TOPIC discussion of Backyard BBQ, grilling, Equipment and just outdoor cookin' in general, hints, tips, tricks & techniques, success, failures... but stay on topic. And watch for that hijacking.


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Unread 03-28-2013, 04:28 PM   #31
ButtBurner
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Quote:
Originally Posted by NCoonis View Post
You're awesome Dave! I am most definitely making all these mods this weekend. I still have other small things like door handles and latches to put on. I'll post new pics after this weekend and let you know how it went.
I would think you would want a larger exhaust than the intake, since hot air expands.

but maybe I am full of hot air, I dont know

there are smoker building calculator sites out there you can check with
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Unread 03-28-2013, 04:58 PM   #32
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Well I'm cooking brisket on Sunday so we'll see what happens. I'll be modifying her all weekend starting with the temp gauge and bigger exhaust and adding a chimney. I'll let you know for sure how it goes with some new pics do my hopefully finished product.
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Unread 03-29-2013, 08:11 AM   #33
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do you have a small fan? use that for extra air flow, of course aimed at the fire box.

just another tuning option
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Unread 03-29-2013, 05:08 PM   #34
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Quote:
Originally Posted by dwfisk View Post
OK I see you are leaving the 2" exhaust open, my bad. I would think you need at least a 3". Look for a custom muffler shop, they should be able to cut an sell you a 3 ft chunk of 3" pretty cheap. It will be galvanized or nickel plated but its OK for the exhaust.

One 3" will give you the same 3.7 square inch exhaust area you have with the four 3/4" inlets.
My math doesn't match your math. We may need a third opinion.

I get:
.5625 Sq. In. for the 4 3/4" ball valves
3.14 Sq. In. for the current 2" exhaust
7.065 if the exhaust is changed to 3"

After running these numbers I'm of the opinion that the OP doesn't have enough intake air. By my numbers NCoonis would have about the right intake by adding 2 1-1/4" intakes to the existing 2. NCoonis, make sure you have and get full flow valves. Not all ball valves have full sized holes in the balls.

My best advice would be to find a pit calculator and run some numbers thru it.
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Unread 03-29-2013, 07:39 PM   #35
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Here is how my math works, I hope area still = pie-r-squared
INTAKE
diameter 3/4 = 0.75 in
radius = 0.375 in
0.375 x pie = 1.178 sq in
4 of them = 4.71 sq in
EXHAUST
diameter = 2 in
radius = 1 x pie = 3.14 blah blah blah
1 exhaust = 3.14 sq in
or
diameter = 3 in
radius = 1.5 in
1.5 x pie = 4.71 sq in
Have I screwed up somewhere?
I would get my exhaust AT LEAST in balance with intake. Actually, I'm a pretty strong beleiver in a wide open exhaust and control at the intake so I would be tempted to oversize the exhaust and go to 4 in. I dont know squat about UDS cookers, but I see a bunch on here with only 2 or 3 3/4 inch intakes so I'm assuming 4 might be enough.

Oh yeah, in my house, pie-r-round, cobblers-r-square (maybe rectangular).

PS: stopped by my local muffler shop and picked up a 3 ft chunk of 4 inch for $20 for another build we are starting.
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Unread 03-29-2013, 07:47 PM   #36
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I would think the 4" pipe is a bit small. Not enough air flow.
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Unread 03-29-2013, 08:15 PM   #37
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Quote:
Originally Posted by dwfisk View Post
Here is how my math works, I hope area still = pie-r-squared
INTAKE
diameter 3/4 = 0.75 in
radius = 0.375 in
0.375 x pie = 1.178 sq in
4 of them = 4.71 sq in
EXHAUST
diameter = 2 in
radius = 1 x pie = 3.14 blah blah blah
1 exhaust = 3.14 sq in
or
diameter = 3 in
radius = 1.5 in
1.5 x pie = 4.71 sq in
Have I screwed up somewhere?
I would get my exhaust AT LEAST in balance with intake. Actually, I'm a pretty strong beleiver in a wide open exhaust and control at the intake so I would be tempted to oversize the exhaust and go to 4 in. I dont know squat about UDS cookers, but I see a bunch on here with only 2 or 3 3/4 inch intakes so I'm assuming 4 might be enough.

Oh yeah, in my house, pie-r-round, cobblers-r-square (maybe rectangular).

PS: stopped by my local muffler shop and picked up a 3 ft chunk of 4 inch for $20 for another build we are starting.
Dave, I could be wrong but I thought the formula for area of a circle was radius squared x pie. So in my case I'd have:
.75/2= .375 radius
.375 x .375 = .1406 radius squared
.1406 x 3.14 = .4415 square inches of one 3/4" circle
.4414 x 4 = 1.766 is my total intake.
A 3" exhaust using the above formula would give me a 7.06 sq in exhaust.
I'm going to look for a airflow calculator now to see where I should be at.
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Unread 03-29-2013, 08:23 PM   #38
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Quote:
Originally Posted by NCoonis View Post
Dave, I could be wrong but I thought the formula for area of a circle was radius squared x pie. So in my case I'd have:
.75/2= .375 radius
.375 x .375 = .1406 radius squared
.1406 x 3.14 = .4415 square inches of one 3/4" circle
.4414 x 4 = 1.766 is my total intake.
A 3" exhaust using the above formula would give me a 7.06 sq in exhaust.
I'm going to look for a airflow calculator now to see where I should be at.
You are right, missed the squared step.
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Home built 24"x72" reverse flow stick burner trailer with 18"x40" grill w/CI grates and upright SS gas oven/smoker.
Home built 48" fire pit with a 30"x30" Santa Maria style ranch grill.
Home built lump charcoal retort, iGrill & a bunch of other cooking toys.
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Unread 03-29-2013, 08:25 PM   #39
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Quote:
Originally Posted by dwfisk View Post
Here is how my math works, I hope area still = pie-r-squared
INTAKE
diameter 3/4 = 0.75 in
radius = 0.375 in
0.375 x pie = 1.178 sq in
4 of them = 4.71 sq in
EXHAUST
diameter = 2 in
radius = 1 x pie = 3.14 blah blah blah
1 exhaust = 3.14 sq in
or
diameter = 3 in
radius = 1.5 in
1.5 x pie = 4.71 sq in
Have I screwed up somewhere?
I would get my exhaust AT LEAST in balance with intake. Actually, I'm a pretty strong beleiver in a wide open exhaust and control at the intake so I would be tempted to oversize the exhaust and go to 4 in. I dont know squat about UDS cookers, but I see a bunch on here with only 2 or 3 3/4 inch intakes so I'm assuming 4 might be enough.

Oh yeah, in my house, pie-r-round, cobblers-r-square (maybe rectangular).

PS: stopped by my local muffler shop and picked up a 3 ft chunk of 4 inch for $20 for another build we are starting.
Yeah your formula can't be right becuase a 3/4" circle has to be smaller than 1 sq. in. You show 1.178.
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Unread 03-29-2013, 10:13 PM   #40
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It's Friday night and I'm growin' tired of runnin' numbers as I'm drinkin' adult beverages.

Here's one calculator.

http://www.calculatorsoup.com/calcul...ane/circle.php
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Unread 03-29-2013, 10:39 PM   #41
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Quote:
Originally Posted by Wyley View Post
Look in the electrical conduit department at Home Depot or Lowes. They should have something that screws right into that bung hole, and even if it is galvanized its just being used for exhaust. You can even soak it in toilet bowl cleaner and that will eat the galvanizing right off of it.
Thats what I have on my UDS with about 30" stack on the exhaust and there is plenty of draw.
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Unread 03-30-2013, 12:50 PM   #42
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how did that thermometer check out?

was it off?
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Unread 03-31-2013, 11:49 AM   #43
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Quote:
Originally Posted by ButtBurner View Post
how did that thermometer check out?

was it off?
Yes it was. I pulled the other one I had off my little weber creation and it read 220-225 in boiling water, so i used it. Not sure what brand it is, its old. My meat therm read almost the same.
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Unread 03-31-2013, 12:03 PM   #44
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Ok I'm mid cook and I determined its a thermometer placement issue. I added a 4" od stack I made with some .032 aluminum I had at work. Now I have 4 ea 3/4" ball valve inlets plus two more 1-1/8" holes with a sheet metal damper.

Didn't have time to to buy a better thermometer by today but the one I'm using is pretty accurate. Its the placement on the door that's the problem. It's reading about 170, but I put the meat thermometer which is also accurate (tested in boiling water) inside on a grate with the probe not touching any metal, and it's maxed out at 200. So I'm somewhere above that I think.

I'll keep you updated on the progress.
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Unread 03-31-2013, 01:45 PM   #45
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It actually looks fine the added intake and exhaust won't hurt. Temp prob issues are your main culprit. That and adjusting to a new rig. Keep firing her up and you will learn how she likes to dance.

One thing that has nor been addressed is grease, I hope you provided a way to drain that baby, because I can imagine that once you fill her up with a full load you will had a lot of grease to deal with.

Welcome aboard neighbor
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