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-   -   DIY Reverse Flow Cinderblock pit (https://www.bbq-brethren.com/forum/showthread.php?t=246017)

sleebus.jones 05-04-2017 07:12 PM

DIY Reverse Flow Cinderblock pit
 
Y'all may remember the cinderblock pit I built a week or so ago in this thread

Well. I'm back with a new and improved version! Some quibbles with the last one:
  • Firebox is too small, requiring frequent tending
  • Small size makes it hard to load...gotta get down on your hands and knees
  • Larger firebox means the inlet has to move up, which will lead to...
  • The pit getting a fair bit hotter where the firebox inlet is
  • Inlet to the pit is oversized for the firebox per a BBQ pit calc page

So. We all know the solution to this: A bigger firebox and Reverse flow! But how do you do it? Well, it's actually pretty easy.

I had to tear the whole pit down, because I had to change the first course. Originally, I had the fire entrance to the pit on the first course. I want it now on the second, so to keep the proper stagger, I had to reset all the blocks. This is why no mortar is good!

https://i.imgur.com/CQnhskel.jpg

Now you can see the inlet placement with the second course

https://i.imgur.com/trQYlRcl.jpg

I upgraded to 3/8" rebar for supporting the plate...a good suggestion from a fellow brethren here. This is where the reverse flow plate will sit.

https://i.imgur.com/kv6RjEtl.jpg

Required more aggressive cutting with the masonry blade to get the rebar to fit.

https://i.imgur.com/c5uDBdkl.jpg

Ok, reverse flow plate is in place, now to cut slots for the rebar to support the grate.

https://i.imgur.com/3l6vdlgl.jpg

There we go. So, you can see the reverse flow plate and the grate here. Slot is about 4" or so at the other end. The area of the slot matches the area of the inlet to the pit from the firebox. With the bigger firebox, now the inlet to the pit is the right ratio so it draws properly.

https://i.imgur.com/kwN2hTTl.jpg

Another view of the slot

https://i.imgur.com/1OLw1dfl.jpg

Oh yes, sweet, sweet room to make a decent fire.

https://i.imgur.com/PW6LNK4l.jpg

All back together. I need to trim the steel plate I'm using to control the inlet air. Looks like I'm gonna need to get handy and learn how to use a torch.

https://i.imgur.com/oIzxBybl.jpg

So today, I didn't do any cooking. I just took it up to 400° to season the reverse flow plate...I had wiped it down with lacquer thinner to remove any stray hydrocarbons and then coated in peanut oil to season. The temp management seemed much more well behaved. The previous version would really swing pretty hard when you added a split.

Future improvements might be a stack with a damper, but what I've got now works pretty well.

Stlsportster 05-04-2017 08:00 PM

I love this build! Just goes to show you don't need to weld or buy a $3000 pit. Can't wait to see how you continue to improve this with each variation. Once you're done you should document the plans so others could follow it!

Now where's the food pron!!!

gtsum 05-04-2017 08:41 PM

Impressive!


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bwram1 05-04-2017 08:53 PM

Quote:

Originally Posted by Stlsportster (Post 3785921)
Just goes to show you don't need to weld or buy a $3000 pit.

...unless żou want, or have a need, to go mobile...as I do.:-D

tom b 05-04-2017 08:57 PM

Bad Azz

sleebus.jones 05-04-2017 09:06 PM

Quote:

Originally Posted by Stlsportster (Post 3785921)
I love this build! Just goes to show you don't need to weld or buy a $3000 pit. Can't wait to see how you continue to improve this with each variation. Once you're done you should document the plans so others could follow it!

Now where's the food pron!!!

That was the idea...a high performance pit that just about anyone could throw together pretty much anywhere in the world.

So, materials for the current build are:

52 8x8x16 cinderblocks. Lowes has them for $0.66, so $34.32
Custom cut 1/8" steel plate top $50
Custom cut expanded metal grate $35
Custom cut reverse flow plate $36
20' of 3/8 rebar $8

So ~$125 for the "build". You'll need a masonry blade for a circular saw to cut the slots in the cinderblocks...nothing else works as well. I realize the steel plate parts can be somewhat difficult to source, but a little research should find some sources for you. I'm lucky to have a BBQ pit fabricator about 10 miles away. The top I have is probably overkill, I'm sure there's cheaper ways to cover it up.

Food pr0n coming in a day or so!!

Stlsportster 05-04-2017 09:24 PM

Quote:

Originally Posted by bwram1 (Post 3785958)
...unless żou want, or have a need, to go mobile...as I do.:-D

Wonder if you could build this on a trailer?

RacrX 05-04-2017 09:29 PM

Daaaang, that's smart!

bwram1 05-04-2017 09:30 PM

Quote:

Originally Posted by Stlsportster (Post 3785985)
Wonder if you could build this on a trailer?

Should be fine as long as you don't hit a pothole. Or a speed bump. Or exceed 25mph. Or take a curve at more than 15mph.

m-fine 05-04-2017 10:37 PM

Quote:

Originally Posted by bwram1 (Post 3785989)
Should be fine as long as you don't hit a pothole. Or a speed bump. Or exceed 25mph. Or take a curve at more than 15mph.

Put the materials on a trailer with sides and assemble on site. Or get a welder and make one out of steel.

55Drum 05-05-2017 08:09 AM

Great build!!! Where's the chimney??

WilliamD 05-05-2017 08:17 AM

Awesome ingenuity!!!! Thanks for sharing!

rus_bro 05-05-2017 08:41 AM

Would anything be better than showing up at a competition with the back of the truck full of cinder blocks on thursday afternoon. 45 mins later you have built an amazing reverse flow pit.

Now we just need to drill some holes for the TelTru Thermo and some spray paint to get the team name on the outside. :)

i LOVE this build and it would ALMOST be worth the a$$ chewing i would get from the wife to build this in the back yard.

rb

daninnewjersey 05-05-2017 08:48 AM

Quote:

Originally Posted by rus_bro (Post 3786196)
Would anything be better than showing up at a competition with the back of the truck full of cinder blocks on thursday afternoon. 45 mins later you have built an amazing reverse flow pit.

That would be insane. Imagine beating some of those dude with their $6000.00 smokers..plus you'd have a lot of onlookers for sure.....:biggrin1::biggrin1:

Stlsportster 05-05-2017 08:52 AM

For the inlet you could just mount a large ball valve on that sheet metal. Then you could adjust airflow at a granular level. Still noodling the exhaust....:confused:


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