Question on evening out temps across the grate

[thsmormonsmokes]

Here's a problem I've been running into.  I've got a Char Griller Smokin' Pro.  I've done the baffle and tuning plate mod, charcoal basket mod, and the stack extension mod, along with a few other minor mods.  (about half way down the page here: http://www.smokingmeatforums.com/t/58778/char-griller-smokin-pro-with-firebox-mods/220).

So with those mods I've been able to get very consistent temps across the grate when I'm firing it up.  It comes up to temp and holds temps consistently within 5 degrees across the grate while the chamber is empty.  It'll stay that way forever on an empty chamber.

But for whatever reason, once I put something on the grate, temps on the SFB side get way hotter.  Sometimes 50+ degrees hotter than the smoke stack side.  I figure it must have something to do with the way the pork butt/brisket disrupts the air flow through the chamber, but I can't make any sense of it.  I've tweaked my tuning plates around, but that doesn't seem to make a big difference.  It's also done this on dead calm, hot days too, so I'm inclined to think it's not wind.  I can't figure out what the problem is.

I've been doing mostly pork butts or picnics lately so I've been able to get away with that, but I want to try a brisket again soon, and I want more consistent temps than that before I try a brisky again.

Any insight?

 

[pops6927]

Are these air temps or internal temps?  

You are introducing mass to your smoker.  Once that gets to temp, it will absorb heat and likewise radiate it, increasing the air temp.  Do you have an equal mass on the other end to counterbalance it?

 

[daveomak]

TMS, morning.....   Take some pics of the inside of the smoker....   How much space is on the end of the tuning plates for return air ???  How much space is under the stack extension ???  Maybe adding an extension to the top of the stack will suck more heat and smoke through the smoking chamber.....  Sounds like an air flow problem that is heating up the firebox....  Can't be sure.... Just guessing for now...   Dave

 

[porterman]

i had a couple fire bricks and put them on the coal holder in the smoke chamber,with an aluminum sheetpan between them,suspended by the lips of the pan. seems to have helped a lot.

 

[thsmormonsmokes]

TMS, morning.....   Take some pics of the inside of the smoker....   How much space is on the end of the tuning plates for return air ???  How much space is under the stack extension ???  Maybe adding an extension to the top of the stack will suck more heat and smoke through the smoking chamber.....  Sounds like an air flow problem that is heating up the firebox....  Can't be sure.... Just guessing for now...   Dave

I'll try to remember to get some pics taken.  My week days have been really busy lately so it could make some time.  But I keep the tuning plates basically together on the SFB side in an attempt to move the heat and smoke more to the smoke stack side since that's where it tends to get colder.  I've tinkered around with them a little, but that doesn't seem to make a huge difference.

The stack extension stops about 1" from grate level.  I'm almost wondering if that's creating a draw issue?  

My last smoke I also forgot to put in a water pan.  I'm sure that didn't help any and I'll remedy that on the next go around.

Are these air temps or internal temps?  

You are introducing mass to your smoker.  Once that gets to temp, it will absorb heat and likewise radiate it, increasing the air temp.  Do you have an equal mass on the other end to counterbalance it?

Those are air temps.  I stick a probe through a cut potato and put it on the grate to monitor cooking temps.  And I've calibrated the probes in boiling water so I know they're accurate.

I typically put the butt dead center on the grate.  I'm wondering if I shouldn't move it slightly to the SFB side of things.  Based on what I'm seeing I think this might be an air flow issue.  That would absorb some of the heat from the SFB and presumably allow better air flow on the smoke stack side of things.