HP loss in the 5000M series

[clarityconnect]

According to the 5000M tractor brochure there is a 15 HP loss between the tractor engine HP and the PTO HP rating. Why is this when the normal loss in almost all other brands and even most of John Deere's other models is usually only about 7 HP. Even in the Kubota M series (M6040, M7040 ) there is only a 7 HP loss. I don't understand why Deere has this huge loss in HP between the engine and the PTO rating.

 

[Bigfoot62]

I've wondered about that myself.

I have the 5085M, and here is the TractorData page for that model: TractorData.com John Deere 5085M tractor information
John Deere claims 70 pto, but it actually tested to 74 hp. Maybe they're just under-rating it to cover themselves. I mean, you can't sue them if it has MORE hp than they claim. Another factor is the Power Shuttle transmission. You do loose a little hp with a torque converter.

Until last fall, when I bought the 5085M, I was running a NH 7610S that was rated at 100 hp engine and 90 hp PTO. The 5M handles all of my PTO driven equipment as well as the bigger NH, most of it in the 540E (economy) mode.

I wouldn't worry about the number too much. They're really good tractors. :thumbsup:

 

[msmud]

Deere's specs usually show PTO power to be 15 - 20% than listed engine power at the tractor rated engine speed, though this isn't always an accurate reflection of a tractor's maximum PTO hp, which can occur at lower rpms. A better source of information is the Nebraska tractor test database (NE Tractor Test Laboratory). On this database you can find most of the 5000M series tractors tested, as well as many of the 4000 series.

For the 5075M, for instance, UNL found that peak PTO hp actually occurred at 1701 rpm with a value of 65.58HP, almost 10% higher than what deere lists at 2200 rpm rated engine speed. The 5065M showed 50.97 PTO hp at 2200, and 56.90 at 1750 rpm. The larger machines can give impressive PTO numbers at lower engine rpm, which Deere takes advantage of with its economy PTO option on some units.

You can tell this sort of thing in the field operating your machine. My 3038e seems to be quite strong bushhogging at 2200 - 2300 rpm, about 10% under the rated rpm of 2500.

 

[ctlguy]

What is even more interesting on the Neb test site is who does not test all of thier machines. Always seemed fishy to me.

 

[Jerry/MT]

According to the 5000M tractor brochure there is a 15 HP loss between the tractor engine HP and the PTO HP rating. Why is this when the normal loss in almost all other brands and even most of John Deere's other models is usually only about 7 HP. Even in the Kubota M series (M6040, M7040 ) there is only a 7 HP loss. I don't understand why Deere has this huge loss in HP between the engine and the PTO rating.

I don't have a direct answer but you have to look at the rating points on the engine and the pto. Are the rpm's at rated power the same for the engine max rated power an the pto max rated power the same? If they're different then part of what you call "loss" may just be the reduction in HP due to a reduction in engine speed. Rating philosophy is dependent on what development testing discovers about a specific engine design.

Remember that the max HP is at the peak of the HP vs rpm curve and is measured or corrected back to the engine flywheel. This is usually a "bragging rights" number that marketing peope like to throuw around.
Max Rated Power can be at another rpm. The pto rating is usually based on continuous operating power through a gear train to the pto output shaft on the tractor whcih is turning at either 540 rpm or 1000 rpm. So gear reduction at the pto input shaft also plays a part.
The two points can be at differnt engine rpms and these rpms can be different than the rpm for max rated power.

With electronic engine controls there can be even more variablity. The control can recieve an input that the pto is selected "ON" and have a limiting fuel flow that causes the power limitation at the same engine speed as the rated max horse power. So you see there are a lot of tools that engine manufacturer can use to confuse everyboy about power out put.

Does this help any?

 

[clarityconnect]

Does this help any?

No. The JD brochure states that the engine RPM is 2200 and that the PTO has a rated speed of 2100 rpm.I don't think that these figures would account for a 15 HP difference. These figures are specified for all the 5065M, 5075M, 5085M, and 5095M tractors.

 

[Jerry/MT]

Does this help any?

No. The JD brochure states that the engine RPM is 2200 and that the PTO has a rated speed of 2100 rpm.I don't think that these figures would account for a 15 HP difference. These figures are specified for all the 5065M, 5075M, 5085M, and 5095M tractors.

The pto rated speed is not 2100 rpm. The pto speed is most likely 540 rpm at an rated engine speed of 2100 rpm. So whatever 100 (2200 -2100 =100 rpm) rpm drop in engine speed is worth in horsepower is not a "loss". It's just reduced power due to reducing the engine speed so the pto output speed is 540 rpm. The difference in hp that is lost through the gear train is the difference between horspower at the flywheel and hp at the pto at 2100 engine rpm.
If your brochure shows the power curve you can easily figure what 100 rpm change in speed is worth. The rest of the pto hp difference is losses in the gear train.
JD could have rated the pto at 2200 engine rpm but then they's have to change the gearing so that at 2200 engine rpm the pto shaft turned at 540 rpm.

 

[AKfish]

I think that the general concensus among most "tractor afficianado's" is that Deere tends to be conservative with Hp ratings on their tractors.

Based upon the Nebraska test results; Deere could have easily "rated" all of the 5000M series of tractor's higher by 5 Hp across the board!

However, when I researched engine performance prior to buying a new tractor; I was very interested in peak torque production at a specific rpm level. Based upon that particular rpm; I looked at Hp and fuel consumption.

If there was a strong correlation with high torque at close to peak Hp with great fuel efficiency -- that was a very strong selling point for me! :thumbsup:

The JD 5000M powerplants excelled by that measure. Compare the fuel consumption of the 5000M's (at least the 5065 and 5075) to the JD 4720.... and then consider the torque and peak Hp....

AKfish

 

[msmud]

The problem for the manufacturer is where in the rpm range to set the linkage of engine speed to the 540 rpm PTO speed. As the Nebraska tests show, it would be most efficient for Deere to make the linkage at 1700 or so rpm with these 5000 series tractors, but then the operator is left with the dilemma of having to adjust ground speed by increasing engine rpm over 1700, such that the PTO speed is "overrun," i.e well above 540 rpm such that attachment gear box wear is increased

The compromise that Deere is making here is to link engine speed to 540 rpm pto speed at higher engine rpms so that the operator has more flexibility with non-PTO considerations like machine speed. For us users, in the case of rough-cut bushhogging in a field where pretty results aren't an issue, we could run the 5000M series down at 1700 rpm for more PTO power at the expense of blade tip speed.

 

[Jerry/MT]

I think that the general concensus among most "tractor afficianado's" is that Deere tends to be conservative with Hp ratings on their tractors.

Based upon the Nebraska test results; Deere could have easily "rated" all of the 5000M series of tractor's higher by 5 Hp across the board!

However, when I researched engine performance prior to buying a new tractor; I was very interested in peak torque production at a specific rpm level. Based upon that particular rpm; I looked at Hp and fuel consumption.

If there was a strong correlation with high torque at close to peak Hp with great fuel efficiency -- that was a very strong selling point for me! :thumbsup:

The JD 5000M powerplants excelled by that measure. Compare the fuel consumption of the 5000M's (at least the 5065 and 5075) to the JD 4720.... and then consider the torque and peak Hp....

AKfish

Remember the Nebraska Test results are for just one engine on one tractor for one model number. That tractor/engine combination is probably really checked out by JD (or any other manufacturer) to make sure it's per spec before that test.

However tractors are built on an assembly line with parts that come in from all over the world. So the worst case engine/tractor combination has to be accounted for so that even the worst build will meet the manufacturer's guaranteed power output. That's why most of these engines put out more than spec power when you test them. A very, very small percentage of machines will just make the spec and that's good enough to ship to a dealer.

P.S. Did you ever find any engine where peak torque was close to peak HP and also had a minimum BSFC?
Just curious because I've never seen any such thing!(not that I've seen it all)

Peak torque occurs at low rpm and peak horsepower at high rpm and min BSFC occurs in the midrange. the slope of the torque curve with increasing rpm is negative so you won't see peak torque at peak power. There are some tricks that can be played with electronic controls to tailor the torque and hp via fuel metering and turbo control but usually at the expense of BSFC. Generally the engine guys produce staright forward engines without control tricks because BSFC is important to the end user. And at this point in time everybody has the same technology to know what to do. Propietary materials or manufacturing processes usually keep the newer manufacturers from achiving the same levels as the Big Guys.