Hi guys.. just browsing and saw some interesting maybe unanswered questions.
tuliku - Post #8141 (
http://www.bbq-brethren.com/forum/showpost.php?p=1686745&postcount=8141) explains a lot with air flow and I put in there area of a circle chart. Please note that the chart is about controlling the INTAKES. Always leave your Exhaust fully opened, once you have figured out how many holes and how big you need. You can use the calculations and convert to metric system. In general, if you have three 3/4 inch holes you would have a total of 1.33 inches squared for the intake, and for exhaust you should have about pi inches or 3.14 inches squared, which you'd get from the typical 2 inch hole in the lid.
Adding some chimney pipe helps a lot to create the draft to pull. It will burn more coals though, however getting high heat will not be a problem.
tuliku !!
When you mention that you only got to 120 degrees, are you by chance reporting in Centigrade? That would be ~248 degrees Fahrenheit. This actually seems very typical.