During my first few cooks with my ST1400, I experienced some long cook times with pork butts - one in excess of 25 hours at 225+f.. The other two cooks were over 22 hours duration and the butts removed at 190f internal temperature. I even checked out the operation of the thermostat and found it to be operating exactly as it should. That is I got approximately the same temperature spread as I was advised I would and the AVERAGE temperature was within 4 degrees of the set point.
For the first 3 cooks, I used a drip pan under the bottom cooking rack that held flavored liquids as per a recipe that I like the sound of. Since it was taking twice as long to cook as reported by others, I suspected that the evaporation effect on temperature from the liquid was keeping the actual temperature around the meat lower than desired. Yesterday I cooked my 4th pair of pork butts and by coincidence these were also the largest I have cooked - just over 9 pounds each. I still injected about 1/2 cup per butt of Cajun butter and spices. This time I eliminated the drip pan. With the thermostat set at 225f, I saw oven temperatures ranging from 219f to 254f. The bottom butt reached 197f in 11-1/2 hours and I pulled that one. It took another 1-1/2 hours for the other butt to reach 197f. The results were excellent but then pork butts are almost bullet proof aren't they?
I am convinced that the shielding effect plus the temperature lowering effect of evaporation can have a dramatic affect on cooking times.
Happy Smokin everyone.