130 Gallon Standard Offset - Ben Hur WWII Trailer

[dacolson]

I’ll run it in a few days. Slammed at work right now. My grate is 5” from the FB end of the tank. The baffle extends 3” above the lower grate and is right up against it. I’ll take a bunch of temps.


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[hogaboomer]

So, basically, the only difference is: yours is 5 inches back from the end plate, and mine is 3. Maybe your smoke and heat is not as constricted as mine, and that gives it a chance to swirl around? Who knows.
Mine is getting tested tomorrow to see if the bottom holes help out. Maybe try it out before cutting holes in the tuning plates to see how it does. Trial and error until I get it the way I want it.

[hogaboomer]

So, the holes in the bottom are not drawing much, most of the heat is still going up the top. I guess I have to try closing off the top gap some, see if that makes the bottom draw. Make the bottom holes bigger, too.

edit: I set a piece of plate up in there blocking off some of the top opening, and got the grill to door thermometer temp down to 50 degrees difference, so making progress.

P.S. This evening I made the bottom hole bigger, like a crescent moon. And I put an adjustable flap up top, so I can close that off however much I need to get the bottom to pull. Test it out again tomorrow. Fingers crossed.

I hope you don't mind the thread drift, Dave - I'll stop if you want.

[av8bdriver]

Glad yall are discussing this, as I am having one built based on yall's designs. SO please keep it going...Sounds like you are already most of the way through a fix, but I wonder if putting a horizontal plate above the throat would help, like jambo pits do/did..

[hogaboomer]

Couldn't hurt.
I ran it again today, got it to within 30 degrees in a 3 inch vertical off the grate. That was with the stack wide open and the vents closed down to where it just kept burning. I tried all different stack and vent positions, that one worked the best.
I just got done making the bottom hole even bigger, and made the top flap where it seals off better. I'm gonna get this thing tuned in if it kills me. The side to side temps are much closer now, too.

[hogaboomer]

Woohoo!!! I got it, now! Finally got it to where the bottom would come hotter than the top, with the top flap closed off all the way. Now I can adjust the flap to even out the top/bottom heat.This is going to turn out to be a good cooker.

[hogaboomer]

I think the firebox height difference may have made this not work for me. My firebox is a lot higher than Dave's.

[dacolson]

Boomer, love the experimentation. Data rules! I have a setup that works great for me but have no idea how other factors effect it. Worried I led you astray but love how deep you jumped into it. Really appreciate you working through some variables and coming up with a setup that’s working. You should absolutely pile onto this build post. Keeping all the info in one place is awesome!!

I am just about to start my 3rd version of this. I plan on only tacking the throat baffle together so I can experiment with it a bunch to dial this in:
- distance from the throat
- height of the vertical above the grates
- angle of the baffle from the throat
- etc

I’m still surprised at how different your experience has been Boomer so I’m relieved you have it dialed in.


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[dacolson]

I think the firebox height difference may have made this not work for me. My firebox is a lot higher than Dave's.

Thanks for the details Boomer. Looks like the top of your throat is about 3” or so above grate level. Mine is right at grate level. I suspect that is a contributing factor. I would guess the heat would leave the FB through the throat at the top and travel over the top of the baffle instead of being redirected upwards sharply to accelerate convection. Just guessing but plan on testing.


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[hogaboomer]

Yep, after I looked at yours it became obvious that that was the major difference. I'm not cutting the firebox off to test it, though.

[dacolson]

Hahaha. Ya. No way.


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[hogaboomer]

Still would be nice to see how your temps test out in the vertical, though.

[dacolson]

For sure. This weekend.


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[hogaboomer]

I kind of like being able to heat from the top and the bottom at the same time, though.

[dacolson]

You have a great work around for sure. I’ll get temps at 4 points - above the top rack, top rack, bottom rack and below the bottom rack - at 4 spots spaced out down the rack. I’ll get some video if I can of smoke movement in the pit as well to show any convection. Not sure yet how I’ll get that but I’ll see what I can get.


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[hogaboomer]

Put it on the rack, and like 3 or 4 inches above. See how much difference you have from the bottom of a brisket to the top. And check the top rack just to see how much hotter it is. I didn't even put a top rack in mine, I was trying to do a basic pit, but it turned a little more complicated than I anticipated.
You say it works good, though - so it must be pretty close. Will be interesting to compare.

[av8bdriver]

Boomer, can you send some pics to show what you have done? Guys, keep me updated and let me know if I should have my welder do something different. He doesn't think he can start on my pit until on September, so i have some time.

Just to review what I'm doing... CC is 1/4" pipe, 60" long x 24" diameter that will be split to release tension. 48" counter weighted single door. FB will be the 3/8" pipe X 24" X 24" with adjustable intakes low on both sides... both at about 80% of total intake area needed. Adjustable Intakes above the door on the end of the FB at 20% of whats required. My throat design is the same one Dave uses on his WW2 smoker, with the 45deg ramp down to the FB damn, and the 3" vertical plate where it meets the grate. 40" long X 5" stack with 5" X 12" collector. The exhaust opening into the collector will be 5" X 22". And lastly, I am adding a rectangular vertical chamber above the firebox. 1/4" plate, 30" tall and 20" wide. It will have a 7-8" stack. Also an adjustable vent going into the FB, as well as one going into the main chamber. Deflector plate right above the FB vent inside the VC. All on a trailer.

If yall see any issues or design modifications needed, let me know. Cant wait and this thread has been invaluable to me.

[hogaboomer]

I put some pics in the Texas Ranger thread.

[dacolson]

Temp test in progress. Been lit for an hour. I have 8 probes going. 4 across the top racks, 4 across the bottom. Running wide open right now.
Top rack, FB to stack:
- 375, 318, 305, 286
Bottom rack, FB to stack:
- 241, 252, 259, 251
The top probe closest to the FB is almost over the throat baffle. The bottom rack probe closest to the FB is a couple inches from the baffle, next to the vertical plate of the baffle.




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[hogaboomer]

6 inches between top and bottom racks? Looks like you have about 60 degrees difference (approximately) in the center of the pit. Not nearly as pronounced as mine was. Mine was 100 degrees in 3 inches.
Wonder what would happen if the firebox was even lower?

[hogaboomer]

Cut your firebox off and lower it 3 inches and report back.

[dacolson]

Go away


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[hogaboomer]

Do it for the science.

[dacolson]

Hahaha. Right.

Top rack is 7” higher. Seriously, I’m good with the temps. Left to right on the bottom rack are close, even right up next to the baffle. The top’s always gonna be hotter. That’s where the hot and fast cooking gets done. She’s dialed in.


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[hogaboomer]

Pretty sweet!