Mack Upgrade

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Chuck Diesel
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Mack Upgrade

Post by Chuck Diesel » November 22nd, 2019, 12:53 am

I purchased the Mack plans a while ago, life happened and I didn't have the time to start a build until now. After looking over the plans I realized that my needs have changed and would like to add another shelf in the CC. Below is the change I keyed into the calculator. The opening at the end of the baffle plate is the same size in cubic inches as the throat. Also, I wanted to go with a single 12" over sized damper on the firebox door. Any feedback would be greatly appreciated to avoid measuring once and cutting three time.

Cook Chamber:25.5 x 49.75 x 32, actual size: 40596 cu

Firebox: 25 x 24 x 25, actual size: 15000 cu, recommended size: 13532 cu, differential: 110.85%

Chimney: 6 x 25.48, actual size; 720 cu, recommended size 750 cu, differential: 100%

Firebox Air Intake: 1 inlet, actual size: 113 cu, recommended size: 45 cu, differential; 261.57%

Throat: recommended size: 120 cu



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Dirtytires
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Re: Mack Upgrade

Post by Dirtytires » November 22nd, 2019, 1:16 am

Not sure if your plan was to just add another shelf (which is no problem) or were thinking of making the cook chamber bigger. I might recommend getting Frank involved if your plan was to increase the cc as he might have some good pointers for you.

The single damper is definitely possible. My first concern is placement as intakes work best located low on the firebox. Second, I have had times when shutting down vents on one side of my firebox (and opening only the other side) has helped with unstable temps due to wind. A single air vent would mean a more complicated solution.



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Re: Mack Upgrade

Post by Chuck Diesel » November 23rd, 2019, 5:30 am

Dirtytires,

In regards to the cook chamber size, the plan was to add another shelf with the same space between each shelf. As I looked over the plans I realized that I would have to add more volume to the cook chamber to accommodate an extra shelf. Once I figured out how much space in between shelves I needed I plugged the measurements into the calculator and adjusted my plan for a larger firebox, throat and chimney. As for the single large damper, after watching multiple videos of people using popular named brand smokers, and using my current smoker, everyone likes to open the firebox door for extra oxygen from time to time. My thinking was, keep it safe and just add a larger controllable vent. I PM'd Frank last month but haven't gotten a response. As I read through a number of similar post, most seem comfortable with firebox measurements within 115% of actual size. Your response about the cook chamber has got me worried. I thought if I modified the cook chamber, firebox, throat and chimney proportionately based on the calculator I'd get similar results close to the original Mack plans... what am I missing??



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Pete Mazz
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Re: Mack Upgrade

Post by Pete Mazz » November 23rd, 2019, 5:57 am

Nothing that I can think of.


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Re: Mack Upgrade

Post by Chuck Diesel » November 23rd, 2019, 6:12 am

Peter,

Thanks for the feedback. I'm looking to start cutting steel the first week of December.



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Dirtytires
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Re: Mack Upgrade

Post by Dirtytires » November 24th, 2019, 7:44 pm

As long as you make all the proper adjustments to sizes you should be fine. I was concerned you were not but sounds like you are on top of it.

The size of the fire (and therefore temperature) is regulated by the amount of air allowed to feed the fire. Opening the door will definitely allow air in but it is extremely difficult to maintain and regulate temperature with such a crude ‘valve’. Tho it will work, a more precise damper will be more efficient in the long run.

Hit frank up again....if it has been longer than a week he needs a reminder.



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