Lets make this dead simple.
A prop is merely another form of wing. If you have 2 wings of identical shape travelling through the air at identical speeds, they will generate the same lift.
Relating this to a propellor, if 2 identical props are turning at the same RPM in the same airflow then they will generate the same thrust as they are merely wings themselves.
If you attach the 2 props to seperate engines, one developing 180hp and one 160hp, then if the props are turning at the same speed with the same pitch, the work being done by each engine will be identical. You can therefore say that if the 160hp engine is maxed out at 2550 rpm, the 180hp engine will only use 160 of its finest horses to turn the prop at 2550 rpm.
The 180hp engine still has some power left to give, which can be utilised either by turning the propellor faster (not always very efficient or effective) or by using a coarser pitch on the blades.
For both engines to be maxed out at the same RPM, the props might be the same make and diameter but they will be set up differently to take account of the different power outputs.
Obs cop