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Big Block Temp Variance

post #1 of 18
Thread Starter 
Yesterday I was smoking 3 racks of spares and two fatties. My BB has four shelves in it. I was using t seperate digital therms. One had a probe in one of the fatties and a probe monitoring the top shelf rack temp. The other two probes I had on racks 3 and 4, or the bottom two racks. I have tested these probes a year or so ago and they were accurate at that time. I noticed the bottom rack (rack 4) had a fairly steady temp of 190*. The next rack up (rack 3) ran around 220*, and the top rack ran a temp of nearly 270*! Has anyone had this type of temp variance with their Big Block? I had the control knob on High and all vents closed to the tab stop. I would have thought my hottest temps would be closest to the flame. The temp here in NE Kansas was lower 60's and a little breezy.

post #2 of 18
i have the same with my gosm it is not the bb the one next to it
the door temp is not the same the rack very 20 to 30 deg from rack to rack one thing help
me put hot water in the water pan i put a temp gauge in the side of mine
at the # 2 rack from top i can put a probe on the rack next to it and will
be 5 to 10 deg off from the side temp
i think the water is blocking the heat from the middle and the heat goes up the side abound half way though the cook all temps will level out
post #3 of 18
Thread Starter 
My temps never did level out but got within 40 degrees or so of top to bottom...
post #4 of 18
i got to where i don't worry abound it much the door is always cool than
the side i go half way between them as long as the inter temp of the food looks good i put new temp gages in the door and side
i try to cook 225-265 it all comes out good but ribs
i can't get my ribs right lol i will keep trying
post #5 of 18
Thread Starter 
It's hard to fail on ribs using the 3-2-1 or 2-2-1 method. With these temp variances, you will just need to adjust the final 1 hour prbably...
post #6 of 18
Knowing that climate can effect temps, I'll tell you my findings when using my big block.
First of all, I never close the top vent, this is needed for proper circulation and helps prevents stale smoke/health hazard as in creosote.

Secondly, I always use a full water pan to help stabilize temps. As the water level drops, so do the temps.

My bottom rack is always the hottest, and as I go up the racks the temps drops. This is with the bottom vents closed to factory settings. It's much like when you travel the valley floor and start climbing into the mountains, the temps start to drop. There can be a difference of 50° from top to bottom. I work it in my favor, poultry on the bottom for higher heat, and ribs higher up for a lower temp. It's all good my friend.
post #7 of 18
Thread Starter 
I don't understand why my temp range would be totally opposite of what you are able to achieve. I do keep my water pan full and use hot water when adding. I had set all the vents per Jeff's recommendations in his GOSM guide at the side of this forum. He mentions to close all to the tab stop. If the closing of the top vent to the tab stop is what makes the difference, and my bottom rack will represent the hottest rack if I open that up, I will have a hard time getting 200* in my smoker. Now I'm really perplexed! Thanks Richoso1! ;o)
post #8 of 18
My GOSM was like that, 50° degrees difference, cooler on the bottom than the top, one thing that will help is make certain the water pan isn't pushed back and touching against the back, I pull mine out to the front of the grates and that allows the heat to rise on all four sides, I installed baffles on the side walls to create some turbulence and redirect the heat into the center of the smoker, I also installed a baffle on the top to keep the heat inside of the unit.

As for the top baffle, after I installed it my propane consumption dropped considerably, I close my top vent down to about 3/4 of an inch open, that is more open vent area than on my WSM (the WSM and the GOSM have about the same volume) and I don't have any problem with creosote or stale smoke.

I have installed a needle valve that allows me to fine tune my temps and I have found when I cook between 215°-225°, with the bottom vents completely closed I have a temp difference from top to bottom, of 15° max.

I hope that helps.

post #9 of 18
Is it a newer big block? If so, from what I've gathered, the water pan and stock chip box are much bigger then the original one. That might play a role in why your bottom rack has a lower temp. The water pan and box might be dispersing more heat out around the lower shelf, resulting in lower temps for that rack, and higher temps on the upper rack.
post #10 of 18
Gene, do you have any pics of your baffle on the top vent?
post #11 of 18
You're describing a some-what similar situation as I had encountered when my Smoke Vault 24 was new, only I went a different direct to correct my issues.

I bent the tabs on the lower intake vents so I can close them up tight, then added a 24" vent stack, and I run the top vent fully open. This gives me more evenly distributed temps from top to bottom, and temp variances from corner-to-corner/side-to-side are reduced as well. Smoke chamber humidity is much higher, and I use approx. 0.5-0.8 quart of water per hour, with 20-30% relative humidity and ambient temps of below zero to ~70* F. I go through a bit more water at cooler ambient temps, just because of higher burner flame to maintain chamber temps.

My theory on the success of this simple mod is, by not allowing any cool air to enter the smoke chamber through the lower vents, only heated air from the burner housing rises through the chamber, thereby creating less chaotic flow and more efficient transfer of heat. Stale smoke/creosote is never an issue, as I'm compensating for the reduced intake air flow by adding the stack for improved draft through the burner housing.

I run my Vault in this configuration for every smoke, except when smoking/drying jerky. Then, I open the lower intakes to remove the humidity from the drying meat, allowing for a faster dry time with lower temps.

This is outlined in my Smoke Vault 24 Product Review...I know we're talking about different manufacturers here, but the smokers are very similar in their basic design.

Here's the thread:

post #12 of 18
Thread Starter 
I purchased it in 2008.
post #13 of 18
SQWIB, here ya go, I posted a thread, 'GOSM Mods' in June 09 in the Propane Smokers section if you're interested.

Eric, you said it a whole lot better than I can, I was eating lunch at the kitchen counter staring at my oven when the light went on, there is very little air intake on the bottom front and even less for the heat to exit at the top, I turned it on to broil and positioned myself so that there was a window behind so that I could see the heat escaping, very few heat waves coming out, nothing like what was exiting the top of my GOSM, I waited until night and put a flashlight inside to see where the air was exiting and I found there is a baffle on top of the oven to keep the heat inside, so I just copied my oven, like you I use less water, also smoke wood and propane.

MoFo, I apologize for hi-jacking your thread, maybe this info will help you.

post #14 of 18
So this is secured directly under your exhaust?
Is the back just like the front of the baffle?
are there sides to the baffle like the front or is that where the smoke exits?
Could not find your post
post #15 of 18
Hey SQWIB, yes it looks the same on the back as it looks on the front and it’s 1 1/8" deep, 16" long, 6” wide with the support tabs 5/8".

I used 1 mm aluminum, that would be about .040" thick, I think that would be 20 gauge.

It’s 6 inches wide, which is big enough to cover the vent and yes it is open on both ends to allow the heat and smoke to escape.

The front side is held with stainless steel bolts the back with pan head sheet metal screws because of the flange at the top of the smoker wouldn’t allow me access to install and tighten the nuts.

post #16 of 18
Thanks, looks like I got my first Mod for my Big Block
post #17 of 18
And to think some folks are worried about a 5 degree variance when cooking. All grills and smokers vary in temperature and you have to learn how to cook with each for the best results. My Big Block is set at the factory suggested vent positions and my "Q" makes my family very happy.
post #18 of 18
But hes talking about an 80 degree difference, not sure if I would want to cook 4 butts on a smoker with such a temp variance, I could live with 30 degrees difference but 80...no way. I would try to fix that somehow.
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