AutoX tire pressures (basic)

[67Rally]

Hey guys (and gals), after a few years of building my '67 Camaro and getting it to run and handle reliably, I finally signed up for my first AutoX event next month.

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.