RandomPerson8008- thanks a bunch for the clarification and it makes alot of sense. i also understand that the ZFW is maximized with the freighter models which limit their range due to the priority of the carrier being the freight.
lastly, seeing as you fly the platform, have you noticed a change in epr when you set it on takeoff roll?? does it decrease/increase at all??
I have only flown the simulator so far...in any case 95% of my company's aircraft have GE CF6-80C2 series engines, as do the simulators. The GE uses N1 as the primary engine indication and does not provide EPR indications. During preflight, the FMC calculates a target N1 value for the engines based on atmospheric conditions and thrust setting selections. The engines spool up to maintain this target N1 after the "TOGA" buttons are pressed at the beginning of the takeoff roll. The N1 % does not change until flaps reach 5 degrees or 1500 ft depending on the departure profile. The thrust change is normally a reduction to climb thrust, however takeoff thrust is maintained until Vref30+98 knots is reached in the event of an engine failure (in which case continuous thrust is subsequently commanded).
Whether EPR indications on Pratt and Whitney and Rolls Royce engines remain constant during the takeoff roll I cannot say for certain because I have no experience with them. Logically the EPR should stay relatively constant once stabilized for takeoff, much like N1, and my differences manuals make scant mention of the subject.