Dashpot is the decay rate of the rpms coming down and finding idle from what i understand. Its usually shown as bypass airflow from the iac at closed throttle vs engine speed. You want to contour this so it will drop quickly at higher rpm's once the throttle is closed and slows as it approaches idle. If it is to fast is will drop right past idle and stall/die. It may just take some trial and error to get it perfect.
I see you also have a supercharger, this will also cause problems since there is excess pressure in front of the throttle plate. You want to keep the dashpot values low since your iac is fed from a pressurize source.
You can also go over too eectuning.org and read up on it there. Im sure theres some good info over there. i think Ive seen you over there? Not sure if im remembering correctley though. Hope this helps.
Also you want to take into account for larger throttle bodies and such.
-Justin