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Upper Vent Modifications to a PBC - Steampunked!* (*Gracias, HC!)

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    Upper Vent Modifications to a PBC - Steampunked!* (*Gracias, HC!)

    Shrouding the need to fiddle in the cloak of the pursuit of perfection, I stuck pipes on my PBC. As HC said, it’s steampunked! I did think it would look rather cool to use copper, and old Brasserie type effect:

    I want to emphasize that this is a totally frivolous exercise in many ways. The PBC works spectacularly. This is just a ‘because it’s there’ type operation.

    I mounted the vents far lower than they otherwise would be (usually they are at the top of any smoker, for the obvious reason that hot air rises). I did this because I wanted to impact the ‘static’ air of the PBC as little as possible, while hopefully getting more control over the burn.
    Expanding on those points:
    1. The PBC doesn’t have a water pan, and has low air flow. The low airflow does two things (IMO): retains a moist air around the meat; allows for a higher cooking temp without drying.
    2. The PBC is by design a ‘set and forget’ type cooker, and it works really, really well. But I’ve found big variances in the operating temp, which results in fretting over the completion time of the food. I wanted to have the control to be able to push it to its key operating temp (275 - 310) in any situation.
    So, I needed a vent system that didn’t drain the PBC of moisture, but still gave enough airflow for temperature control. My conclusion was to lower the vent, essentially beneath the meat hanging zone. The hypothesis is that the air will move through the fire basket and small portion will vent through the pipes and that additional flow will be enough to be impactful to the chamber temperature.

    The additional radiant heat from the higher aiflow of the coals should raise the chamber temp, hopefully with minimal addition air movement within the drum.

    Defining the measure for control:

    Typically the PBC gets very hot at the start (380F), then falls back to an operating temp of 275 to 300, stays there for a while (potentially several hours), then falls back again, quite dramatically. A quick stoke of the coals and cracking the lid raise the temp back up (perhaps repeating the initial step of 380 then 275). But sometimes it drops back further and / or more quickly, requiring a repeat of the lid cracking exercise.

    I will point out that the finished product in the above scenario always seems to be great. So why worry or change anything? Because sometimes you want a bit more predictability.

    So the measure of success is: Can the vents keep the temp at the optimal operating temp with limited trimming.

    This allows some ability to compensate for a) Lots of meat in the PBC and more thermal energy is needed and b) later in the cook (after the first 2 - 3 hours) when some fiddling with the coals is required to keep in the optimum zone, c) jacking the heat up for final extra crisping of poultry skin, without cracking the lid or yoyoing the temp.

    The build:

    Pretty staightforward. Just drilled holes and added parts. There is one internal piece (45 degree elbow) that I’m using to bring the vent hole out over the fire basket. It’s detachable (just slides on) so the basket can be pulled in and out.

    Then the sequence of parts from inside to out - ¾ nipple, washer, PBC, washer, cuff (female to female) ¾ elbow, male ¾ to 1”, 20” of 1” pipe, cap (drilled out to ¾).
    Stack length: I looked for a ratio / hueristic for stack length to width or draw, and all I could find was “the longer the better, unless its too long, then its worse”. I presume that the exhaust cooling excessively is the issue, so 20” of copper pipe is probably not the best. To compensate, I used 1” pipe.

    To limit the flow out of the stacks, I simply put corks in them. I cut a cork at an angle, so it can cut off half of the exhaust or more.


    3 parts:
    1. Did the air flow the right way?
    2. How it performs in various set ups, no meat
    3. How it performs with meat.
    Q1: A question was raised about if the vents would just act as another intake. I hadn’t considered this. The first test was with a very small coal load (10?) and some smokey wood. It went the right way, billowing out of the stacks. Phew!
    Q2 & Q3: I had 4 basic tests: Half open and full open. Short stack (10 inches) or long stack, pictured. There is also a temporal component - how it acts through time. E.g. both open will give a different effect in the first hour that then the last.

    The Results:

    I’ve got graphs, but with all the different combinations they are noisy. Suffice to say, I’ve determined that the pictured set up seems to work. Here’s a graph, but note that the x axis is not scaled correctly (something about the igrill2 output format means excel is not recognizing it as time)

    The graph shows about 6 hours, with only one lid opening (the big zigzag). No meat. You can see at the end, the coals were done. You can also see that at the beginning, I just let the PBC heat up with both vents open, just to see where it would settle. Normally, it would got to 380 - 400 and fall back. In this case it climbed to 360 and sat there.

    When I cut the flow to half, it trailed off back to just over 310 or so, and seemed to stabilize there. This was the fourth hour of the cook. I then shut them both as a precursor to testing if the pipes could revive the fire. It took an hour to fall back to 260. I then opened both, it staged a 40 minute rally but was then about done. I suspect the long sustained high heat in the first three hours had reduced the duration of the cook.

    Chamber temp: Without meat, both open seemed to hold 360F. Which is good, because it indicates that more heat can be generated for the larger cooks, or the temp raised for crisping. Half open, just above 300. I let it run for an hour at both settings just to be sure, but I’m reasonably comfortable that these are the ‘natural’ levels.

    With meat (6 racks of ribs, so significant) both open ran at 315 or so. Half open ran between 265 and 275. towards the end of the cook, I opened both vents up and it started to climb back up above 300 and sit there.

    Exhaust was interesting to watch. It’s never aggressive with the PBC, however, the pipes were about equal with the upper vents (just eyeballing) hopefully indicating that the chamber airflow was not dissimilar to the original settings.

    The ribs: Top notch. Super smoke ring - actually one of the best I’ve had out of it. They were ‘The Pit’ quality. Meat was everything you’d expect it to be.

    Stack length. I monitored the exhaust temp in addition to the chamber temp to see the effect of short vs long. Long stacks ran 100F cooler than the chamber temp. Short stacks less than 50 cooler. However, in either case, the chamber temp was about the same indicating (I think) the draw was similar enough to make no difference.


    It worked. I can get higher temps, and have some level of control. However, it’s not responsive. You can see from the diagram that both heating and cooling took time. It will gradually get to its new max temp then stay there, it’s not a quick jump.

    However, the max temp is pretty stable, and if the max temp is stable, then temperatures beneath that should be stable too and reachable by trimming.

    Judging by the ribs, the cooking chamber is just as moist as it always is. The pronounced smoke ring and the rib succulence was testament to that.

    I suspect that Jerod and Spinakers’s setup are far more responsive, and may well have a higher max temp., and when cooking large amounts of meat, probably / definitely better. Whether there is more drying of the meat when small amounts of meat is used will have to be settled at the ‘The Pit First Annual Cookoff’!
    But the pipes are pretty, in a steampunk kind of way!

    Last edited by mtford72; December 15, 2014, 02:58 PM.

    Wow - so much info to digest here! Awesome write up!!!

    I want to mod the airflow on mine so the constant "lid cracking" (especially with big cooks) can stop.

    I looked into something as simple as how the UDS kit has an adjustable damper in the lid; then I saw Jerods stacks up high and was intrigued.

    Now your design with the stacks down low at the fire basket height - my head is swimming (not to mention to outright coolness of the copper pipes and brass fittings)!

    Its like a crazy combination of a supercharger / turbo and a jake brake for your PBC!

    Thanks for posting all of your designs and research - excellent craftsmanship!


      Very nice work. I love the graph, thats what I was looking forward to the most with this post. You gave some great clear and consice information. What I found to be most interesting was that when you went to "half open" at the near beginning the temp spiked up to 390. That was 20 degrees more that when the stacks were wide open. I wonder if closing the vents half way created an acceleration of the air through the stacks. Much like air flowing through a canyon of tall buildings in the city.But then as time passes by the temp cools because of lack of oxygen in the half open position. I just found this to be interesting.

      Also, I was wondering next time you are cooking, check the inside of the elbow on your stack. I put my finger in mine and it was full of water. Thats testament to just how much moisture is in the cooking chamber. I'm almost considering drilling a small hole on the back side of the elbow to drain that water off. It should remain air tight when there is water in the pipe, and just drip out slowly. My thinking is don't want water to sit inside the pipe and begin to rust. However, since your using copper you may not have to worry as much as I do.

      Great job on this. Your craftsmanship looks really good and the copper really makes it look purdy. And Sign me up for the First Annual Pit Cook Off. (How much would it cost to check my PBC? Maybe I'll just buy him a seat with me in first class....) This is one of those experiments that you would only get here, my friend. Thanks of the opportunity to tinker with some cool and fun ideas.
      SMOKE ON!!!!!!!



        Cheers guys!

        HC - I suspect that the Jerod / Spinaker approach of high on the barrel is probably better, simply for control purposes. My set up might potentially keep the barrel air more moist, but with a few pieces of meat in their its like a steam bath, so probably giving up a fraction of that for a considerable gain in responsiveness is wise. (I will just add that I've only tried cooking meat on it once, so I may change views on that if I find a trick to make it change temp faster).

        Spinaker - tons of water coming out of the pipe initially! I hadn't sealed the gap, because I was testing the different lengths. I put some silicone gasket tape at the join of the stack and elbow (just see a red dot in the first picture, right hand stack) and that now drains it back into the barrel.

        A point to note about that - with the 45 elbow reaching out over the coals, all that condensate drips back out onto the coals. That might make it even moister in there, hence the great smoke ring. (it was noticeably more pronounced than usual, and I only used apple, rather than cherry which always darkens the meat (at least on surface)).

        That spike in the graph was a lid cracking. I wanted to check if the coals under the 45 elbow were burning preferentially (I wasn't convinced either way). That was the only time I cracked it during the cook.

        As an aside, a PBC is definitely carry on only!


        • Spinaker
          Spinaker commented
          Editing a comment
          Can you imagine how that would make the cabin smell?? LOL.

        • mtford72
          mtford72 commented
          Editing a comment
          I was flying Aeroflot in eastern Russia once (once is enough). About 3 hours in, the guy infont of me undoes the string tied around the waist of his woolen great coat and pulls out a large paper wrapped flat thing (this was pre 911, so just inspired curiosity). Turns out it was just about a whole smoked salmon.

          It stank. And stank. And stank. It induced dry heaving in just about everyone in that section of the plane. The only unaffected parties were him and his dog that was tied with a piece of string to his armrest. The dog went effing nuts.

          Our 'concerns' fell on deaf ears with the stewardess, because by that stage our translator had completely stitched up the entire group. Instead of providing the Russian for 'coffee with milk' or whatever, he'd taught us to say 'I love you' and 'I will go to all of your discus competitions'.

        • HC in SC
          HC in SC commented
          Editing a comment
          I never considered the fact that you did actually create a couple of J traps for water. Wait, or would it be a P trap. Geez....my plumbing is about as good as my electrical work. Lol

        Mine are responsive, with the extensions, to get SUCTION. Just one little 90 didn't do crap.

        A note about the Pit Barrel folks not cracking the lid.

        If you wrap, pretty much at the stall, like they do, you will get a much quicker cook:
        1. The meat will climb quickly in that ultra-humid environment
        2. That ultra-humid environment is in the foil, NOT the cooker. I think this has a more profound affect since you are cooking OVER your heat source.


        • HC in SC
          HC in SC commented
          Editing a comment
          Great explanation!

        If you find they ultimately don't do what you want (but it sounds like you're happy), you could try dip tubes, or extensions inside (reverse flow style) the new pipes extending upward inside to grab air from the upper chamber and vent it back out. I don't know, I'm not an engineer, just throwing a crazy idea out there since we're in mod mode.
        Last edited by Huskee; December 15, 2014, 03:35 PM.


        • mtford72
          mtford72 commented
          Editing a comment
          They seem to do the job, Huskee. That extension inside the barrel bringing it over the basket seems to work just fine. There is heat from the fire hitting it straight on and therefore going straight up the stack. Once that flow is established, I think the chances of it reversing (and them becoming intakes) are pretty slight.

        • Huskee
          Huskee commented
          Editing a comment
          I had the dip tube idea when I had a water heater maintenance issue. It got me thinking about you guys doing mods to your PBCs. Obviously if it works it works! Maybe this idea could benefit the next guy though.

          Nicely done my friend!

        Matt took the words right out of my keyboard. I was going to say what he said but....................



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