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I was debating for a long time whether it's worth it making this post but here we are prompted by latest TTWT video.

A beautiful custom setup with this mower and with laser box blade those 2 are something special.
However it was mentioned that tractor seemed happier PTO rpm wise when at slightly lower engine rpm. I very rarely use full rpm on my tractor and any other diesel equipment. There are several reasons why.
Firstly diesel engine usually provides maximum torque and power at much lower rpms when compared to gasoline engine. This is the same for engine in our 4052R which I will get back to later.
Passive regen is one hell of a mystery on these machines but from what I read it happens when engine is working in its optimal power window. From what I observer over hundreds hours of field work is that passive regen usually happens around 2100-2200 engine rpm when using taxing implement. Think mowers, baler, ground engaging stuff. When using higher rpms sooth build up was higher when compared to using lower rpms than 2100.
Lastly every time I we were given guidelines by our dealer on how to operate any implement we were always told to keep engine rpms in moderation. From my experience there is really no need for pushing 540. I have not noticed any difference while mowing, tilling, baling, wood chipping,... We even have some implements that suggest running specifically at 450 PTO rpm, not higher, that translates roughly to 2100-2200 engine rpm range.

When our tractor was at dyno what I really wanted to see was the torque and power curve. Here is the partially translated version with some personal information removed but should be sufficient to further my case.

4052R stock engine is represented by dashed line. As can be (not so clearly) seen maximum power is available at roughly 2100 engine rpm.

I am using this post mainly as callout to @Tractor Tim . Would it possible to show these power curves from your dyno measurements? Comparison of both stock and turbo 1R engines might have drastically changed them as well. (Using this method as I hope it will work unlike YT comments and might be beneficial for others.)
I would also like to see dyno power and torque curves of other models and engines if you guys have them available and anything else that might be added to this topic.

By no means I am saying that these engine can not run at full rpm. I am simply suggesting there is basically no good reason to do so.
The manual for my tractor says that the engine can be run at full load between the engine speed for 540 PTO RPM with economy PTO engaged (just shy of 1600 RPM) and the engine speed for 540 PTO RPM with regular PTO engaged (just under 2100 RPM.) Full throttle is 2200 RPM. The only time I run it completely wide open is when roading the tractor, for the extra mile per hour of road speed. The only PTO driven implements I use at less than 540 PTO RPM are a PTO driven broadcast spreader in some situations (the PTO speed controls the broadcast distance) and the posthole auger, which is only supposed to be run at about 300 PTO RPM according to the manual. Everything else gets run at 540 RPM, and since my transmission does not have the option to have the economy PTO, it's 2100 engine RPM. I'd guess the tractor is running at 2100 engine RPM about 2/3 of the time as most of the time I am a cutter, mower, tiller, square baler, generator, etc. that is supposed to be run at 540 PTO RPM. The generator MUST be run at 540 PTO RPM or the frequency and voltage are off. The others I run at 540 RPM as their capacity decreases with decreasing PTO RPM down to a certain point, and then below that performance just stinks (particularly mowers.) I just maximize ground speed at full PTO speed rather than throttle back to decrease PTO speed as I get done faster. Also, the power peak on my engine appears to be close to the full PTO speed, so being at a lower RPM than that results in being bogged down if I hit a heavier spot with a more power-hungry implement rather than having the engine RPM pull down a smidge and power through it.

I don't have the Bluetooth dongle to check soot level on a cell phone but my tractor does an active regeneration cycle exactly every 100.4 hours. There is supposedly a maximum engine hour interval between active regenerations and since it is so consistent with the regenerations, I suspect I am hitting the hour limit rather than a soot load limit so what I am doing is fine.

I don't have the full power curve for my engine but Deere says it makes a peak 74 HP at 2100 RPM and makes peak torque of 224 ft-lb at 1600 rpm (68 HP.)
 

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Full rpm on a tractor is somewhere about 3000 rpm. The Benz diesels of old revved to 4,300 rpm and could run there all day long. The VW TDI revved to 5,000 rpm.
It depends on the engine. Most of Deere's current diesel engines have a rated speed of 2100-2200 RPM and redline is 100-200 RPM above that. Most of their >2 cylinder engines in the past were in the 2200-2500 RPM range, and the old Johnny Poppers ran between 800 RPM and the mid-1000s RPMs.
 
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