Did it work? Did it increase airflow? How did you test and verify your experiment? I guess a simple way to test, IMO, would be to fire it up and settle in at a target temp without the stack then install it and see where it settles..
I like where your going with the experiment and the way you attached the tube to the can then to the lid.. now I'd like to see some numbers. Keep in mind that the length and thickness of the pipe has an effect on the temperature and thus the speed of the gasses moving through it. The will be an "optimal" length.
As an experiment this looks interesting. I personally don't see the benefit. If you want higher temps drop a split log on your coals. You'll be at pizza oven temps in 5 minutes or so. Also, as a matter of practicality, how are you gonna check your food? You gonna pull that hot piece of metal off every time you open the lid?
You've just begun to peek into the rabbit hole of curiosity, young Jedi. Report your findings.