Pit Building Ratios

Alien BBQ · Posted: Dec 10 2006 Post subject:

Too many margaritas before I type equals addition letters (and thoughts).
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sheddcanyon · Posted: Dec 10 2006 Post subject:

Alien, can you answer this question:

"If I'm using two stacks, does each stack need to be 3/4 the length of the cooker, or can the combined length of both stacks equal 3/4 the length of the cooker?"

I have the flexibility to make both stacks 3/4 the length, but I'd prefer to go a little shorter.

Second, I'm not sure I'm calculating my air intake for the firebox correctly. My firebox volume is: 30 x 18 x 18 = 9,720 cubic inches. If I understand your rule, does my air intake need to be 9,720 x .003 = 29.16 square inches?

Third, could you state the formula for calculating volume of a cylinder? I tried the site that mine suggested but couldn't figure it out.

Fourth, do you make your margaritas with cointreau or triple sec?

SoEzzy · Posted: Dec 10 2006 Post subject:

skybob · Posted: Dec 10 2006 Post subject:

After all this talk about pie, I just had a thought. Ouch, that hurt. There's some carmel apple pie in the fridge. Hmmmmmmm. Now for the cool whip. Smile

BoilermakerFan · Posted: Dec 10 2006 Post subject:

skybob · Posted: Dec 10 2006 Post subject:

Triple sec for me

sheddcanyon · Posted: Dec 10 2006 Post subject:

Grand Marnier. Interesting concept, we'll have to try it.

So Ezzy, thanks for the formula and the answer to the lengths of the stack.

sheddcanyon · Posted: Dec 10 2006 Post subject:

After proving to myself once again that I am entirely incompetent at math, I found a great website for calculating volume:

http://www.online-calculators.co.uk/volumetric/cylindervolume.php

One more question: I am running a 6" pipe from my firebox to my cooker (a little bit like Rubit's T-bar concept). Calculating the volume of a 6" diameter pipe, 6" in height, I get a volume of 169.7 cubic inches. Using Alien's rule of firebox volume x .008, I get 77.76 square inches. Am I going to run into trouble with too big an opening between my firebox and cooker?

Alien BBQ · Posted: Dec 10 2006 Post subject:

It is way past 5pm so my thoughts may not make any sense but here goes. On the intake 5x6 should do it. Keep in mind that this allows you to go hotter. You will probably never open it past half way for smoking; but BBQ temps could have you open it all the way once in a while.

Double stacks = half the 3/4 length based on the distance from that stack to the pit.

SoEzzy seems to have a good handle on this so go with his verifications of your figures. Your final question does call for some consideration because of the disproportionate size of your fire box. I really would like to know the set up and how the heat comes in before I commit to an answer.

One last thing, keep in mind that this is a work in progress; we may still have to tweak the formula here and there.
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SoEzzy · Posted: Dec 10 2006 Post subject:

mine · Posted: Dec 10 2006 Post subject:

rubit wrote:
A square tube even though it has more area than a round pipe of the same inside diameter. will suck the same as the round pipe.,

Why is this?

How do you quote in the light colored boxes?

skybob · Posted: Dec 11 2006 Post subject:

The corners have so much turbulence in them that they don't contribute very much to the total draw. They do look cool, though.

mine · Posted: Dec 11 2006 Post subject:

hey Skybob, thanks for the info.

I'll procede with my square exhaust, at least now it will match my intakes.

Alien BBQ · Posted: Dec 11 2006 Post subject:

Hey guys, I have reformatted my question and call for info into 7 different poll questions. If you could input your info there I would appreciate it.
http://www.thesmokering.com/forum/viewtopic.php?t=5467
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Richard · Joined: 04 Jan 2007 Posts: 9

This is very intersting information. I have some questions about a non offset smoker. If I could get some help it would be appricated. My main cooker has charcoal trays in the bottom directly above the charcoal there are water trays that cover roughly 80% of the charcoal above the water trays is the grate. This is primarly a whole hog cooker. It does a good job but I think it could do better. To cook a hog we use around 160#s of charcoal. I can hold the tempeature at 225 pretty good but can not get it above 300. Also in the early morning hours I start have trouble mainting tempeature. I do not have any vents in the bottom for the charcoal. and only have 2" short pipes 8" in the lid. However the lid is not sealed well and I have alot more exhaust from aound the lid than thru the pipes. Any opions would be appriciated

skybob · Posted: Jan 04 2007 Post subject:

Richard, I'd say that you need to get your charcoal elevated off the floor by a mesh screen or PSP type stuff to get combustion airflow to the charcoal. I personally would put in some combustion air vents in the bottom, below the charcoal trays with some means to throttle the air so temps can be regulated. Take a couple pictures and post'em here with the dimensions and we'll give it a whirl.

Alien BBQ · Posted: Jan 04 2007 Post subject:

I agree. No air control on the bottom with elevated charcoal is really not control at all. Once this is accomplished, I believe you will get hotter temps with less charcoal.
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Richard · Joined: 04 Jan 2007 Posts: 9

Currently my charcol is placed on 2 slide out trays that are 1 1/2" from the actaul bottom of the grill. The bottom of the trays are soild and I can easily cut the plate out and put in exapanded steel. I just do not have very much room for the ashes below the trays. I am not so worried about reaching high temps but I would like to be more efficient. The charcoal being smothered adds smoke but I know some will argue that it is not good smoke. I would also like to improve the overall air flow if yall think it will help. I built the grill a year ago and have cooked on it alot for fun and in about 10 comps it does good but I want to improve it. I will post some pictures and or a sketch with dimensions if some body can tell me how.
Thanks for any help you can give.

skybob · Posted: Jan 05 2007 Post subject:

The smoke off smothered charcoal isn't a real good tasting smoke, Alien can speak more on that subject, I believe. Putting the air inlets and doing the expanded metal grate screens should help you get your temps up and control them better at the same time.
As for posting pictures, there are some primer courses at the top of either this or the General threads. Good info that is useful other places also.

Richard · Joined: 04 Jan 2007 Posts: 9

Here are a couple pictures and a not-to-scale sketch of the inner workings.

http://i143.photobucket.com/albums/r138/richardcbc/GrillSketch.jpg
http://i143.photobucket.com/albums/r138/richardcbc/P1030024.jpg
http://i143.photobucket.com/albums/r138/richardcbc/P1030025.jpg
http://i143.photobucket.com/albums/r138/richardcbc/Elloree066.jpg

The access door to the charcoal trays is directly under the rear bumper the trays slide out for loading. The water tray fill tube is located behind the tag.
I will be cutting the solid bottom out of the charcoal trays and replacing it with expanded steel and I can vent the charcoal with the access door. I am intersted in opions on the air flow around the water trays and thru the grill. My stacks are only 2" pipe. Any opions are appriciated. We are cooking in a comp in 2 weeks and I am planning to load it up with thermometers before we put the meat on to check for even heat.