Originally Posted by bearfoil
The 900 is quite different from the others, in RPM, discrepant RPM, and bearings.
MAX PERMISSIBLE ENGINE ROTOR SPEEDS
(Based on the limits stated in FAA TCDS for RB211 TRENT 500-series and 900-series, % converted to RPM)
.........Trent 500 ... Trent 900
HP ...... 12954 ....... 11932
IP ......... 9045 ......... 8117
LP ........ 3608 ......... 2787
Are these the differences you are referring to?