If you're interested, here are my results, for Fedco# 2-304:
dP of heatercore @ 0.5 gpm: 1.5" (0.054 psi)
dP of heatercore @ 1.0 gpm: 4.0" (0.14 psi)
dP of heatercore @ 1.5 gpm: 8.5" (0.31 psi)
dP of heatercore @ 3.5 gpm: estimated, 4.48 psi
Not terribly accurate, procedure described
here.