Question about running open headers and valves?

Cold air doesn't get in to damage, but the valve needs a bit of back pressure. The valve will burn, crack or check, or the valve seat will do the same. The common damage is a small w crack on the valve face, which then leaks compression gases into the hot header resulting in erratic backfire and misfiring. The lack of back pressure can be compensated for by richer mixture, or grinding a wider seat. Get used to lapping in valves, or find some high performance sodium valves and stelite seats. You could run dumps, and only open the headers for short blasts.