12 - 12.5 lbs. depending on weather. My car weighs in the neighborhood of 3250 lbs. with the driver and a SBC. I do about a 6-second burnout.
Works best for me anyway. Any lower and my car gets to feeling a bit unstable down at the big end. Best thing is just play with it. Make small adjustments and take temperature into consideration. Check pressure just prior to, and just after, the run. You will see how much it can change, again depending on weather. My two cents anyway.
Good luck.