Simplify the following text for a Grade 11 native English-speaking person.
Original: Built to replace the previous Class 43 ( better known as the InterCity 125 ) , the Class 91s were given the auxiliary name of InterCity 225 to indicate their status as a new version of the 125 and their envisaged top speed of 225km\/h ( 140mph ) .
Simplified: The Class 91s were given the auxiliary name of InterCity 225 to indicate their envisaged top speed of 225 km\/h ( 140 mph ) .