Autocross Tire Pressures (basic Q's)

[67rally]

I posted this over on Lateral-G but haven't gotten a response yet...

I just signed up for my first AutoX in my with my '67 Camaro. I was looking for some decent baseline tire pressure recommendations to start the day out with, but didn't get much help from the manufacturer. I don't have a set of dedicated track tires/wheels yet, so I'm going into it with my Nitto 555's. 245/40/18 up front and 275/40/18 in the rear.



Is there a general rule of thumb (i.e. 5 more psi than on the street, or increase one/not the other, or start at xxx psi and work your way up or down based on wear patterns) that would be a good starting point? Thanks.