PDA

View Full Version : DIY Reverse Flow Cinderblock pit


sleebus.jones
05-04-2017, 07:12 PM
Y'all may remember the cinderblock pit I built a week or so ago in this (http://www.bbq-brethren.com/forum/showthread.php?t=245482)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!


Sent from my iPhone using Tapatalk Pro

bwram1
05-04-2017, 08:53 PM
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
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
...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
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
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
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:

tonyjohnson619
05-05-2017, 09:06 AM
I love the new version of the pit. Can't wait to see the food pron

sleebus.jones
05-05-2017, 09:29 AM
Great build!!! Where's the chimney??

For right now, it's accomplished by sliding the plate on the top back to create a slot. Cheap & cheerful approach. I had a shot of the top in the other post, but it looks like this:

https://i.imgur.com/lBVC9hzl.jpg

I am thinking about putting a stack on it, but that would require a 4" hole in the plate, a stack (duh!) and a damper. Maybe in the future when my torch skills develop!

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

Ha! I'd love to see that! That would be so awesome. It's definitely doable too, but it's gonna be ~1,500 lbs of blocks! Might need to split the load. Honestly, it doesn't look too bad once it's all together. Some paint on the outside would go a long way to making it look acceptable.

For a thermo, I drilled a hole in the top, and then I just drop a thermocouple down there. Since the only access to the inside of the pit is by just simply lifting the top off, I'd be concerned about breaking the probe part of the thermo off when you set it down, unless you were really careful. Also, with the thermocouple, I can feed enough wire to get it to hang right at cook level over the meat.


BTW, I have a great idea for a team name: "Some Assembly Required" :becky:


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:

There'd be a lot of :shocked: and :crazy: and then :doh: when they taste what comes off of it. I'm doing the first cook today on the new configuration, but if it's better than the previous configuration (which cooked awesome BTW) it's gonna be downright silly.

This was the results from the conventional flow configuration:

http://i94.photobucket.com/albums/l95/sleebusjones/1a57389d-dd46-43b6-a235-f28091bdd6a0.jpg (http://s94.photobucket.com/user/sleebusjones/media/1a57389d-dd46-43b6-a235-f28091bdd6a0.jpg.html)

Those were done with rub only, no wrapping, cooked straight through at ~275°. The were freakin' delicious.

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:

Well, this thing does love air. For the inlet, calcs are recommending a 19 SqIn opening. That would be a HUGE ball valve. For an intake, I really like this design:

https://i.imgur.com/hLyLfA8l.jpg

Cheap and gives you micrometer control over the intake, and you can open it way up with no restrictions. Also, remember these are just stacked blocks; the firebox is naturally leaky.

Calculated dimensions for the stack is 4" x 25". The reverse flow sheet is 15.5" x 28". I may have some further tips for reducing the throat size, calcs now say it's 27% oversize, but I have ideas for reducing that. I'm going to probably draw this thing up in SketchUp so everyone can see how it goes together.

Cool thing is that it's scalable. You can make it as big as you need. Blocks are cheap! :thumb:

roncoinc
05-05-2017, 10:15 AM
Made my morning !! :)

newtwoq
05-05-2017, 11:22 AM
This is pretty epic!

jason&egla
05-05-2017, 12:50 PM
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:

Season 2, Episode 6 of BBQ Pitmasters had the teams doing a whole hog on cinder block pits. It aired back in 2010. Fun to watch, really leveled the playing field.

gtr
05-05-2017, 12:55 PM
Loving this - thanks for posting!

cats49er
05-05-2017, 03:46 PM
You surely make Hank Jr proud. A Country Boy Can Survive . This Redneck country boy loves it.:thumb:

bbqwizard
05-05-2017, 04:50 PM
Way cool!

JDM46
05-05-2017, 06:10 PM
Will it cook your Killer Sausage?:razz::-P

dsp2
05-05-2017, 07:56 PM
That is freaking beautiful. Thank you for sharing, and congrats!!

Happy Hapgood
05-05-2017, 08:38 PM
Very Cool!

m-fine
05-05-2017, 10:07 PM
Well, this thing does love air. For the inlet, calcs are recommending a 19 SqIn opening. That would be a HUGE ball valve. It would be a large ball valve, and sliding or rotating dampers are a lot easier and cheaper to build...BUT I hate to sound like a broken record, but the online calcs are a big pile of BS with no valid science or engineering behind them. Pay them no attention and rely on your observations and experience. You likely already know way more about cinder block pits than the guy who published the calculator.

sleebus.jones
05-06-2017, 10:19 AM
Will it cook your Killer Sausage?:razz::-P

You bet! I originally put this together to use the "free" pecan sitting around in my yard, rather than buying pellets. I'll be able to hang it on smoke sticks and let it rip...although with summer here it'll be hard to hold temps down enough to do it. Sounds like you're still enjoying it up there!

It would be a large ball valve, and sliding or rotating dampers are a lot easier and cheaper to build...BUT I hate to sound like a broken record, but the online calcs are a big pile of BS with no valid science or engineering behind them. Pay them no attention and rely on your observations and experience. You likely already know way more about cinder block pits than the guy who published the calculator.

Yeah, a 5" valve which is big by itself AND a non standard size. all of which means $$.

The online pit calculators may be a big pile of BS, but they give one a starting point and they don't seem to work too bad. Before I made the changes, the firepit was more like a rocket stove, and I'd get flames about a foot into the cook chamber...not good for holding the temps down! With the new config, even though I haven't been able to choke down the inlet to the pit, the reverse flow plate is sized for the smaller inlet, so I'm getting some benefit from that. This has helped by making the temp control of the pit more manageable. It has much less of a tendency to run away. I tend to believe the stack size, and once the fire stabilizes, a 5" round hole would provide plenty of control. I keep it pretty choked down because there's a fair bit of leakage between the blocks that feeds the fire.

Sorry folks, no cook pics from yesterday. Didn't have my phone with me out there. Just did some thin pork chops, cooked slow. I will say that the heat is VERY even across the surface of the grate. No more hot spot by the firebox inlet. My bigger problem is that with all this cooking on the pit lately, I've run down my stock of pecan, hahah! Need to wait for the trees and wind to drop more. :pray:

JDM46
05-06-2017, 12:59 PM
[B] Sounds like you're still enjoying it up there!

Best Sausage Recipe that i have found in a long time.
Have passed it on to a dozen or more.

Big Swole
06-26-2017, 03:44 PM
Sub'd to refer back to soon. Want to build one someday. Thanks for posting.

Smilerb
06-27-2017, 06:51 AM
A simple way to do your chimney would be to cut a vee shape at the front of the top plate and continue to slide the plate backwards and forwards.

4ever3
06-27-2017, 09:25 AM
That's a sweet cooker!

Mike Broughton
06-27-2017, 10:15 AM
Awesome job

orangeblood
06-27-2017, 10:35 PM
very nice...admire the horse sense ingenuity