Glen

You want to start out with the lower pressure in the rear on a 911. The rears work harder and build more temp/pressure than the fronts.

mitch236

Really the most important thing to do is to come into the hot pits after around 6-8 hot laps and see what the pressures are. Then bleed them down to your goal (if needed). After dialing in your hot pressures this way, check the cold pressures the following morning to get a rough idea of starting pressures. Remember, as you noted, ambient temps have to be taken in to account.