Guess it depends on your setup. I have a built y8 running 16psi with dsm 450s and 3in. like you. My timing is advanced 5 degrees. The ignition timing is what should retard based on boost. It is supposed to progressively retard the ignition timing throughout the power band, per manifold pressure. If you have the ECU chipped, usually they will map the ignition timing like mine, or MSD makes a boost retard controller which essentially has the same effect. My personal opinion is not to mess with those things unless you get it on a dyno... if you set the cam timing wrong, it is really easy to loose a lot of power if the valves do not operate when they are supposed to. good luck.