A little off the subject, BUT would these "same engines", making different HP, only make as much HP as required to do the job?
Example, if both were brush hogging and it only took 30HP to do the work, would a JD 5425 with 65 PTO HP be making 65HP? And a JD 105M with 90 PTO HP be making 90HP doing the same job? Or would both only make as much HP as required to do the work? Both running at PTO rpm.
I do not know the answer, just something this thread got me thinking about.
Nope;
Think of the power as a "withdrawal on demand" (-:
You put whatever attachment you decide on the 3 pt, set the rpm to get 540 (or 1,000) at the shaft and go to work.
The governor maintains that speed.
If your implement runs into heavy work the engine will tend to bog down, but the governor will attempt to maintain that speed.
Horsepower is a measure of a rate of doing work, i.e. it is force times speed.
A 20 HP load on a 65 HP tractor will "draw" 20 HP, no more.
To get that same tractor to put out it's 65 HP you would need to increase some combination of speed, working width, toughness of task, etc by a factor of just over 3.
By analogy, if you plug a toaster or coffee pot into a portable generator or a wall outlet it will still draw the same 1,000 maybe 1,500 Watts.
The 3 Kw generator puts out 1/2 to 1/3 of it's power capacity for this.
The local power station ? Well, it probably has multi-megawatt capacity, point is the toaster or coffee pot only draw the same load, regardless of the capacity of whatever they are plugged into.