SS,
almost there. IEPR because on the RB211 engine the pressure from the 'back end' of the engine is integrated/combined with combustor pressure. So you've got integrated pressure (P.int) and fan pressure (P.fan), actually a mixture of LP turbine pressure (P.E) and combustor pressure (P4), though I'm not sure of the exact ratio of these pressures. The equation for IEPR on an RB211 is as folows:
Integrated Pressure (P.int)/Fan Pressure (P.fan) = IEPR
Brgd's
N1 Vibes