Edited:
I found the answer, overall the compression was lowered from 1:7 to 1:6,5, resulting in the difference.
So overall this is it:
HL 120
2600 RPM 265 PS
2800 RPM 285 PS
3000 RPM 300 PS (1:6,5 Compression) 320 PS (1:7 Compression)
HL 108
2600 RPM 230 PS
2800 RPM 260 PS
3000 RPM 270 PS (1:6,5 Compression) 300 PS (1:7 Compression)
The RH 8/803
https://invenio.bundesarchiv.de/invenio/direktlink/4db8866a-4eae-41b9-91f1-38d927f91d2d/
D.652/17
HL 120 Manual
Some more insight should D.653/51 Panzerkampfwagen IV, Ausführung B - Motor
Werkstatthandbuch zum Maybach-Motor HL 120 (?)
bring, as it will most likely have the RPM an PS, a document specifically for the engine.
Further Books, hidden for space saving.
Waffen Arsenal
300 PS / 3000 RPM
British Preliminary Report No.5 Pz III.
Die deutschen Panzer, 1926-1945 - Ferdinand Maria von Senger und Etterlin - Google Books
Google Books
Google Books
320 PS
US tactical trends
Google Books
Google Books
Google Books
285 PS at 2800 RPM
Google Books
8 Likes
Documentation for the Ford GAA shows that it output 525 horsepower at 2800 RPM, however when saying the actual rated horsepower it is always 500 horsepower at 2600 RPM. Crews could push the engine to 2800 if they wanted (and some actually just outright removed the governor and could therefore push the engine to 3800 before valve float), but obviously 2600 RPM was the recommended limit.
I imagine a similar thing is happening to these engines, with 3000 being the recommended maximum RPM but the engine being capable of 3200. In fact I’m just going to go out on a guess and say that most tank engines were probably capable of going to a higher RPM, higher horsepower output if the driver wanted to push the engine past the suggested limit.
Yeah, i know, for the German Engines its “Dauerleistung” (Constant power) here 2600-2800 RPM 265-272 PS and Höchstleistung (Highest power) 3000-3200 RPM 300-320 PS. First used generally on moving, the other in combat IF needed. The engine is however not governed.
Iirc, there were tests to 3600 or so rpm. However they came to the conclusion a new engine is better, than to shorten its lifespan.
Tho this topic wasnt so much so to see what the top is, but to clear some confusion, as i now have seen 3 sources, where they mixed up the RPM. Another sources i found (primary german that is) also has 2600 RPM 285 Ps.
Where i also came to the conclusion, that some other german engines are also at Dauerleistung and not at Höchstleistung in game.
I will say though, the horsepower values don’t really make any sense.
To get a good idea, horsepower is just RPM × torque (at that RPM). This means that engines have two peaks: peak torque and peak horsepower, which happen at completely different RPMs.
We can get an idea of how the torque increases and decreases by taking the horsepower and dividing by the respective RPM. So:
- 265 ÷ 2600 = 0.1019
- 285 ÷ 2800 = 0.1018 (or 272 ÷ 2800 = 0.0971)
- 300 ÷ 3000 = 0.1
- 320 ÷ 3200 = 0.1
Since the highest “torque” value out of all of these is achieved at 2600 RPM, it is very safe to say that peak torque is achieved somewhere below (or at) 2600 RPM. Therefore, from that point on, torque decreases.
That makes the 3000 and 3200 RPM figures not make sense. They are equal, which simply does not match any gasoline engine figures I have ever seen. They make even less sense with the 272 PS figure, since it would mean torque increases from 2800 to 3000 RPM (again, to my knowledge it should only decrease, at least in engines like these)
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Sry, i have no idea about engines that much. Tho i also saw 320 PS at 3000 RPM. Once again the values are a bit over the place and it might be that they for the documents started to simply smooth the numbers, in general.
This is from TM 9-1731B which is a technical manual specifically for the Ford GAA.
You can see the torque and horsepower lines, and you can also see that, despite torque decreasing past a certain point, the horsepower still increases (even thought horsepower is torque × RPM, the increase in RPM is sufficient to compensate for the decreasing torque).
Point is: once peak torque RPM is reached, torque only goes lower as RPM increases. However the figures you have given show torque staying the same even after peak torque has been reached (do notice that in the graph I have shown torque starts declining faster with higher RPM, so it’s even weirder that at such a high RPM the German engine would output even similar torque values).
So they make me skeptical.
2 Likes
So you are saying, they should have more HP at 3000 and 3200 RPM?
The exact opposite.
If 272 PS is correct, then the 300 and 320 PS values are senseless. They would require torque to go up past 2800 RPM when at that point it is going down.
But even if 272 PS is wrong and it is actually 285 PS, the 300 and 320 PS values are still inconsistent, since they show the same torque value between 3000 and 3200 RPM, when again, it should be going down. In fact, the drop in torque between 3000 and 3200 RPM should be larger than the one between 2600 and 2800, or 2800 and 3000, since torque decreases faster as RPM increases.
So either 300 and 320 PS are wrong and should be lower (if 272 PS is correct), or 320 PS is wrong and should be lower (still higher than 300, probably).
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Think of it like this: after 2600 RPM, the increase in horsepower should become slower and slower with higher RPM.
From 2600 to 2800 RPM, we go from 265 to 272 PS, an increase of 7 PS. Now, from 2800 to 3000 RPM, we go from 272 to 300 PS, which is an increase in 28 PS, which doesn’t make any sense given the previous 7 PS increase.
So let’s discard 272 PS, and go with 285 PS.
So, at 2600 to 2800 RPM, we go from 265 to 285 PS, which is an increase in 20 PS.
Then, from 2800 to 3000 RPM, we go from 285 to 300 PS, which is 15 PS. So far, makes sense.
Then from 3000 to 3200 RPM, we go from 300 to 320 PS. The increase is 20 PS. Completely inconsistent.
So, potentially 3200 RPM 310-315 PS or so?
That seems more probable, but there’s doesn’t seem to be any documentation for 310-315 PS.
Actually, i just noticed, the 3200 RPM is from my memory, but i dont even find the 3200 RPM number anymore, just 320 PS in general. Could it be 320 PS at 3000 RPM (like 2 books say)? Or at what RPM 320 PS?
320 PS at 3000 RPM would be… a bit ridiculous with the other values in mind. It would contradict with the other stated figures more than the slight discrepancies I’ve already mentioned.
For example, the figures you have say 300 and 320 PS at 3000 and 3200 RPM, which already isn’t super realistic because that means at these two RPMs the torque is the same when we know it should be lower at 3200 RPM.
With 320 PS at 3000 RPM the horsepower increases from 2800 to 3000, even though it should decrease, and it is not a small increase either. The torque at 2600 RPM, assuming a 265 PS value, is 0.13% higher than the torque at 2800 RPM with 285 PS. Meanwhile, the torque at 3000 RPM with 320 PS would be 4.65% higher than the torque at 2600 RPM.
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So 320 PS at something like 3300-3400 RPM seems realistic? Because i have seen 2 books and the 2 German Docs, but no RPM given.
I’ve quickly plotted this graph which shows how the torque “curve” would look like with the different RPMs for the 320 PS value. Red is at 3200 RPM, blue is your suggested 3300 and green is 3400 (keep in mind, the Y-axis is not showing actual torque values, since PS/horsepower is torque * RPM * a specific constant, and that constant doesn’t really matter for this point).
Both green and blue seem like plausible curves, at least more than 320 PS being at 3200 RPM. Only time will tell I guess, hopefully with the Pz.IV related document. Even just knowing the peak torque RPM would be helpful.
It should also be noted that you should look into what RPM is used for the top speed of vehicles. With exception to the electric drives of the Ferdinands, engine RPM is directly related to the top speed, since the speed of the sprocket is literally just the engine RPM multiplied by all the gear ratios of the tank.
What this means is that an increase in RPM could lead to an increase in top speed, if the top speed in the documents is written at 3000 RPM.
