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Discussion Boards > Active Subjects > Messages as Posted > Size Tractor Needed Forum

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 10-25-1999, 00:00 Post: 9098
John Rich



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 Tractor Horsepower

Could someone please educate me on tractor horsepower and how it is measured. I have seen the terms net, gross, and nominal in discussing a tractor's horsepower. Is there a difference between the US standard and the Chinese standard. I am being told that the Hubei SN304 is a 38-40 horsepower tractor, but the manual and specs state that it is 30 horsepower and 22 kilowatts. Please help. Thanks.






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 10-25-1999, 00:00 Post: 9099
MichaelSnyder

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 Tractor Horsepower

John,I would assume there are many variations to these terms, therefore I'll give you what understand them to be. I welcome corrects or alterations to my understanding. First off, Gross,peak or max HP is the maximum HP the unit is capable of producing at a certain rpm. Gasoline motors for example, peak hp may come at 500-1000 rpms shy of redline. Net, nominal, usable HP is what is actually "usable". Or peak HP minus any frictional losses (gears,ect..). PTO HP is always less than Gross. For example, Our 20hp Hydro unit puts out "about" 16 PTO HP, gear units are slightly higher (17HP). As far as any variations between Asian/American standards, 1 HP equals 746 Watts. Regardless of country. ~22K Watts is correct for 30 hp. It is likely 38-40HP is Gross engine HP, and 30 is the net HP after it travels through the tranny,tires, ect.. To be honest, to only lose 8-10HP is a faily efficient unit. OMOSmile






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 10-25-1999, 00:00 Post: 9109
Jack in IL



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 Tractor Horsepower

The Society of Automotive Engineers Standards J1995 for Gross HP and J1349 for Net HP ratings of gasoline and Diesel engines spell out the engine "accessories" used when the engine is tested. Power, Torque, and Fuel Consumption are measured as a function of engine speed. The engine is usually run at full throttle as a "brake" applies more and more resistance load to slow it down. The primary differences in the 2 tests are that in the GROSS HP test, the air inlet system and exhaust system are optional at the call of the manufacturer (usually not present or the effects are subtracted out) and the Cooling Fan is not used. All of the above "accessories" are required for rating Net HP.Net HP is usable "flywheel" power with the engine installed in the vehicle. Gross Power is sometimes called "bare engine" power. It is often (but not always) the number used in advertising since it is the highest. The test results can be reported with the engine producing "intermittent" power or "continuous" power. Continuous rating is usually about 80% of intermittent. Continuous would be most meaningful for applications like generators. Most tractor applications only require intermittent power. PTO HP is what would be measured by a dynamometer attached to the PTO of the tractor so it reflects power train losses. PTO HP is approximately 85% of Net HP for many tractors. It will be slightly lower with hydrostatic drive due to the power consumed by the pump even with the tractor not moving.As an example, at the rated engine speed of 3200 RPM, the JD 955 has 35.3 GROSS HP, 33 NET HP, and 27 PTO HP (hydrostatic).Even though "power is power," when comparing specs of different tractors you have to be careful to use the same basis--gross, net, PTO, intermittent, continuous, etc. The problem is that sometimes the basis of the test is not provided in the information you have available.I hope this isn't more than you wanted to know.






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Discussion Boards > Active Subjects > Messages as Posted > Size Tractor Needed Forum

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