Engine gross power vs. Engine net power vs. PTO power: Kubota Review  -- Kubota Tractors Discussion Forum and Review Engine gross power vs. Engine net power vs. PTO power: Kubota Review -- Kubota Tractors Discussion Forum

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 09-13-2006, 14:11 Post: 135157
DenisS



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 Engine gross power vs. Engine net power vs. PTO power

I understand PTO power is what is actually transmitted to the PTO shaft. But what are gross and net figures measuring?






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 09-13-2006, 16:26 Post: 135165
Art White



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 Engine gross power vs. Engine net power vs. PTO power

Gross normally is with out water pump alternator or any other apendages to the power where net includes them. Pto is at the rear of the tractor accounting for all power loses of hydraulic pumps as well as transmission and drive train.






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 09-13-2006, 16:33 Post: 135167
DenisS



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 Engine gross power vs. Engine net power vs. PTO power

Art,
So when an attachment is rated for a certain HP range of a TRACTOR (where PTO is not specifically mentioned), it would be more correct to look at the net, gross or at the PTO?






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 09-13-2006, 17:33 Post: 135170
greg_g



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 Engine gross power vs. Engine net power vs. PTO power

Not sure what value the gross number would be, other than advertising maybe. From the aspect of work, net engine horsepower is what you want to know. PTO horsepower is how much of that net engine horsepower that is available at the PTO spline. When the owner's manual doesn't specify, you can ballpark the PTO hp by subtracting 14% from the net engine hp.

One you didn't mention is drawbar horsepower. That's of interest to owners of ground engagement equipment. How much can it pull. It's a somewhat archaic rating nowadays, but drawbar hp is ballparked by subtracting 14% from PTO horsepower. Example: my KAMA has 45 (net) engine horsepower, ~39 PTO hp, and ~33 drawbar hp.

//greg//






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 09-13-2006, 18:14 Post: 135171
earthwrks

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 Engine gross power vs. Engine net power vs. PTO power

And you have to take into account the different types of drive trains: pure hydrostatic pump-to-motor, pump-to-motor-to-gear transmission, etc. My hydrostatic NH has less wheel horsepower to the wheels than the same non-hydro CUT. With my machine, engine power goes through a hydraulic pump then to a hydraulic motor which then powers the 3-range gear transmission.


If you a google search for Nebraska tractor tests, you should find all kinds of into dating back to the early 1900's as they ahd to compare all machines with the same criteria.






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 09-13-2006, 19:46 Post: 135174
Art White



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 Engine gross power vs. Engine net power vs. PTO power

With the new tractor ratings of net engine being more advertised then PTO, which is all that counted till the 80's when the compact tractors started showing up in force,I'd wonder that many short line companies might not be figuring on that for the operation of their equipment. For us here many tractors will do just fine on the flats with a mower but when they hit a hill that tells what the engine do! Drawbar horsepower is a number that has gone by the way side as how do you rate it? Dirt is not concrete and there are many ways to set tractors up for different performance.






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 09-14-2006, 08:02 Post: 135184
Murf

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 Engine gross power vs. Engine net power vs. PTO power

As EW mentioned, and Art alluded to, the efficiency of the drivetrain can be very important in certain situations.

The Gross -vs- Net hp figure is the only measure of the 'rolling' efficiency of a tractor, big or small.

In applications such as loader work, or pulling hay wagons or trailers, the Net hp is the only real yardstick you have to judge available power since most small tractors, as Greg mentioned, are not drawbar hp rated.

When you see a PTO implement, like a tiller, rated for hp, they mean PTO power, usually they state not only the minimum hp required, but the size of the gear box capacity. This is not just to limit damage, but as a guide of how sturdy it is built. For things like a a rear blade though, it is Net hp they are talking about. I can put a BX sized blade behind my 'Bota, but if it catches on something the tractor will definitely do some damage to it, likewise, my 1,000 pound box blade would likely do some damage to a BX too.

Best of luck.






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 09-14-2006, 08:12 Post: 135187
DenisS



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 Engine gross power vs. Engine net power vs. PTO power

If a rear mower is operated at standard 540rpm, what kind of damage can a tractor do to the mower if the mower is rated say between 25 and 50hp and the tractor Net HP is at or above 50hp? The rpms stay the same, there's a sheer bolt / slip cluth to protect against obsticles, why have a maximum HP rating in this case?






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 09-14-2006, 08:26 Post: 135188
earthwrks

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 Engine gross power vs. Engine net power vs. PTO power

Denis: Typically when a mfg. rates their product they (hopefully) have done some extensive testing. That said, some one determined that after a certian HP things start breaking or wearing rapidly. The shear pin for a 4' cutter won't be the same size as one for a 6' for reasons such as there's heavier/thicker blades or rotating mass that can cut more at one time, which means the drive train has withstand greater shock loads more often.






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 09-14-2006, 08:49 Post: 135189
Murf

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 Engine gross power vs. Engine net power vs. PTO power

Not only that, but when the mower, as a complete unit, is designed, it is assembled out of a bunch of individual components, most made by another company, like the 90 gear box.

They know, that in the case of your example, that an average 40 hp tractor will load up and lose rev's under a heavy load of wet grass. The operator will then do something to reduce that load, slow down or raise the deck or both.

Put that same mower on the back of a 100 hp tractor, and you likely wouldn't even know it was overloaded, that is until the gearbox grenaded from the heat and wear of the overload. I've seen exactly that happen. An orchard near me has a little tiny 90 hp Carraro tractor, they use a 4' mower on the back to go between the rows. Someone thought they could save money by buying a 4' mower intended for a small CUT. It only lasted a few months before they showed up at my place asking if I could weld the gearbox back together, it had snapped clean through in the neck.

Best of luck.






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Discussion Boards > Active Subjects > Messages as Posted > Kubota Review Forum

Thread 135157 Filter by Poster:
Art White 4 | DenisS 4 | earthwrks 2 | greg_g 1 | Murf 3 | Peters 2 |




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