Carpass,
EPR has no particular infulence on a FADEC engine, compared to a hydromechanical controlled engine, as JFD said, itīs just a relationship between the pressure in the inlet versus the pressure in the exhaust. But if you consider the way it is measured, then the fun begins.
EPR on most comercial Jets is TOTAL pressure in the exhaust diveded by TOTAL pressure in the inlet, PT7/PT2 on a JT9 as an example, but the total pressure in the inlet changes with Airspeed, thus appearing that with higher speed you lose power compared to the same powerlever angle at a lower speed. This is especially important in the T/O roll with autothrottle engaged, at a certain speed, normally around 60 to 80 knots, the autothrottle system will no longer be alowed to adjust engine power until after liftoff, this is called "clamping"
Hope this might help you, good luck.
Brgds
Doc
[This message has been edited by DoctorA300 (edited 21 March 2001).]