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Q-talk *ON TOPIC ONLY* QUALITY ON TOPIC discussion of Backyard BBQ, grilling, equipment and outdoor cookin' . ** Other cooking techniques are welcomed for when your cookin' in the kitchen. Post your hints, tips, tricks & techniques, success, failures, but stay on topic and watch for that hijacking. |
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02-11-2013, 04:54 PM | #1 |
Found some matches.
Join Date: 12-14-12
Location: Tucson, Arizona
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UDS Exhaust - Help
Question and Request:
Built (building) first UDS: second on the way when this one complete. Just cooked pork butt and it came out great, but had to mess with intake quite a bit. There are 3 3/4" intakes; 2 with caps one with ball valve. The exhaust is a 1 1/2 metal stack. Got it going with minion method and closed all intakes but 100% on ball valve. When I got home 8 hours later internal (Maverick) smoker temp was 175 F and meat was 150F. This has occurred every time I close off with caps and leave ball valve open 100%. Played with intakes (cap on / off) and it is touchy. The unit is air tight when everything is closed and vent stack is closed. My thought, but let me know if I am wrong; the 1 1/2" exhaust is causing problem. Love the way it cooks but cannot get it to hover at 225 like you guys. Thanks |
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02-11-2013, 04:57 PM | #2 |
somebody shut me the fark up.
Join Date: 10-16-10
Location: Culver City, CA
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I leave one cap off and adjust with the ball valve and that works for me. I cook a lot hotter than 225 though - more like 270 to 300. My exhaust is 2" btw.
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50" Klose BYC, Spitjack XB85, 22.5 WSM, Backwoods Chubby, UDS, WRK, 26" & 22.5" Weber Kettles, Jumbo Joe, WGA, WSJ/MUDS, Kanka Grill, a piece of expanded metal I throw over the fire pit sometimes, Stealthy Black & Vol Orange Thermapens Displaced East Tennesseean Proud recipient of a Tick Former outlaw MOINK baller, now IMBAS Certified, but still lookin' over my shoulder. "Relax, it's only BBQ." - Bigmista, 2013 "Don't worry about playing a lot of notes. Just find one pretty one." - Miles Davis Avatar by my son! WTFWGALD? |
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02-11-2013, 05:03 PM | #3 |
Found some matches.
Join Date: 12-14-12
Location: Tucson, Arizona
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GTR. Thanks.
that sounds a lot like what I do although getting to stabilize at one temp is difficult. You don't think the exhaust then is any issue? |
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02-11-2013, 05:06 PM | #4 |
somebody shut me the fark up.
Join Date: 07-04-09
Location: Jonesboro,Tx
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If you had read the Mother of all UDS Threads this has been discussed at great length and you would know that the optimum exhaust size is 2". I run 3 3/4 intakes 2 caps and a Ball valve like gtr 1 cap off fine tune wit the valve and I too cook 275-350. If the exhaust is to small it damps the fire.
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I'm a Proxy Vegetarian> Cows eat grass & I eat cows. |
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02-11-2013, 05:09 PM | #5 | |
somebody shut me the fark up.
Join Date: 10-16-10
Location: Culver City, CA
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Quote:
As far as getting it to stabilize - are you allowing time for the temp to settle in? Some folks fiddle a lot and that can lead to fluctuating temps.
__________________
50" Klose BYC, Spitjack XB85, 22.5 WSM, Backwoods Chubby, UDS, WRK, 26" & 22.5" Weber Kettles, Jumbo Joe, WGA, WSJ/MUDS, Kanka Grill, a piece of expanded metal I throw over the fire pit sometimes, Stealthy Black & Vol Orange Thermapens Displaced East Tennesseean Proud recipient of a Tick Former outlaw MOINK baller, now IMBAS Certified, but still lookin' over my shoulder. "Relax, it's only BBQ." - Bigmista, 2013 "Don't worry about playing a lot of notes. Just find one pretty one." - Miles Davis Avatar by my son! WTFWGALD? |
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02-11-2013, 06:03 PM | #6 |
Found some matches.
Join Date: 12-14-12
Location: Tucson, Arizona
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Thanks again.
I try not to fiddle, leave it there 30 min etc. Changing the exhaust and work from there. Thanks for the help. All the best |
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02-11-2013, 06:48 PM | #7 |
Full Fledged Farker
Join Date: 12-02-11
Location: chicago, illinois
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I don't know that 2" is the optimum exhaust diameter. Weber uses 4 - 3/4" that equates to an area of 7" on the 22" wsm and is fully capable of smoking hot and fast. A 2" exhaust has an area of well over 12 square inches which I believe without any damper control is overkill for the UDS.
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02-11-2013, 07:07 PM | #8 |
is One Chatty Farker
Join Date: 08-24-08
Location: Los Angeles
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I also have no problem with my stock exhaust vent on my Weber lid.....which is much smaller in area compared to a full 2" exhaust as mentioned above.
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....UDS....Mini-WSM....Midi-WSM....Mod-ECB....22.5-OTG....34"wood fired pizza oven.... |
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02-13-2013, 12:56 PM | #9 | |
is one Smokin' Farker
Join Date: 09-13-11
Location: Fort Smith, Ar.
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Quote:
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[SIZE=2][B]Jim Boston[/B][/SIZE] [B][COLOR=black]Current Smoker[/COLOR][/B] [COLOR=red]"The most reliable, easiest to make at home, Smoker [B]"The UDS"[/B] W/ an Auber temp. Controller w/ 20CFM Blower.[/COLOR] [FONT=Arial][B]Future Smoker [/B][/FONT] [FONT=Arial]$5438.25 Total BYC Smoker!![/FONT] [SIZE=2]Some people spend an entire lifetime wondering if they made a difference in the world. But, the Marines don't have that problem. [/SIZE] [SIZE=1]Ronald Reagan, President of the United States; 1985 [/SIZE] |
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Thanks from:---> |
02-13-2013, 01:14 PM | #10 |
is One Chatty Farker
Join Date: 08-24-08
Location: Los Angeles
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Ok, I can see that. Then how about eight 1/2" holes on a flat drum top? The total area of those eight exhaust holes are significantly smaller than a single 2" exhaust.
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....UDS....Mini-WSM....Midi-WSM....Mod-ECB....22.5-OTG....34"wood fired pizza oven.... |
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02-13-2013, 01:46 PM | #11 |
Full Fledged Farker
Join Date: 12-02-11
Location: chicago, illinois
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Domed lid, flat lid, exhaust is exhaust. Weber uses a 3 to one ratio in intake vs exhaust. If you look at the pbc threads, the unit has a massive 3" that is perhaps 30% blocked and 4 exhaust holes where the rods go through. In the PBC videos they even go on to say while the intake is fixed, they recommend that even if you're only cooking on the grate to still insert the rods to prevent the pit from getting too hot. So in this instance the pbc probably uses a ratio higher than the weber and they have a flat lid. The idea of thermo dynamics on a domed lid vs flat with regards to the size of the exhaust is absurd.
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02-14-2013, 09:20 AM | #12 | ||
is one Smokin' Farker
Join Date: 09-13-11
Location: Fort Smith, Ar.
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Quote:
Quote:
The whole effect of heat rising and creating a draw up through an exhaust stack is thermo dynamics and fluid dynamics at work. If you think its absurd, your absurd.... I have personally experimented with diferent length exhaust tubes from the barrel flat top and I can with the exact same inlet openings, change the temp by as much as 50degrees with a longer exhaust tube. I currently use a 6" exhaust but with a 12" stack the drum will run 50 degrees hotter than the 6" with the exact same setup.... with the normal offset location of the bung hole on a flat top drum the heat on the side oposite the exhaust will rush up against the top of the flat lid and turbulate causing a high pressure zone(turbulent flow), where the heat that rises adjacent to the exhaust opening will rocket straight up and out the 2" exhaust (laminar flow) causing a vaccum(low pressure) and thus a positive flow or a draft in the upward orientation.... With a domed lid the heat all rushes up toward the center exhaust and out, thus the webber lids usually can get by with a much smaller exhaust because of this effect. (the eight circumferential holes would eliminate the turbulence since the hole are all equidistance from the center thus requireing less voulmetric flow) If you notice the exhuast on a weber usually comes out with a fairly high flow rate and a nice amount of force. Conversely try looking at a drum with an offset exhaust, where the exhaust comes out a failry low flow rate.... but with a higher volume. It's all about volumetric displacement, how much air can you move thru the inlets up through the coals across the food grates and out through the exhaust.. Now, Im done with this. This place was not meant to argue or point finger at each other and call each others ideas absurd, Instead we should be considering all the things each other have to say in the intrest of our mutually shared hobby and passion... This was not meant for the person who simply wanted to discuss this topic, have a nice day.. Heres a little light reading for you... http://francesa.phy.cmich.edu/people...s/chapter9.htm
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[SIZE=2][B]Jim Boston[/B][/SIZE] [B][COLOR=black]Current Smoker[/COLOR][/B] [COLOR=red]"The most reliable, easiest to make at home, Smoker [B]"The UDS"[/B] W/ an Auber temp. Controller w/ 20CFM Blower.[/COLOR] [FONT=Arial][B]Future Smoker [/B][/FONT] [FONT=Arial]$5438.25 Total BYC Smoker!![/FONT] [SIZE=2]Some people spend an entire lifetime wondering if they made a difference in the world. But, the Marines don't have that problem. [/SIZE] [SIZE=1]Ronald Reagan, President of the United States; 1985 [/SIZE] Last edited by razrbakcrzy; 02-14-2013 at 09:55 AM.. |
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02-14-2013, 10:42 AM | #13 |
Knows what a fatty is.
Join Date: 11-06-07
Location: Arcadia Florida
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Could be your fuel.
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02-14-2013, 10:49 AM | #14 | |
Full Fledged Farker
Join Date: 12-02-11
Location: chicago, illinois
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Quote:
In the end if we are talking about smoking temperatures without any type of stoker system four 3/4" exhaust holes are enough. If you might want to cook hotter than 350 then I would say you would need to add additional intake and exhaust. |
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02-14-2013, 10:51 AM | #15 |
Is lookin for wood to cook with.
Join Date: 02-04-13
Location: gilbert az
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A 2 inch hole has an area of 3.14 square inches
8-1/2" holes have an area of 1.57 square inches 4-3/4" holes have an area of 1.76 square inches 3-3/4 holes have an area of 1.32 square inches |
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Thanks from: ---> |
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