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tej

question on HP

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arnoldir
Hello Tej, Horse Power is a calculated value for ability to do work. Torque x RPM. An analogy would be Watts of Electricity, Power = Watts = Voltage x Current In a closed system ( the tractor) Energy In (Gasoline) - Frictional Losses = Work Done. The rated HP of the motor is all you get, if the RPM is cut down by gearing you get more Torque. I could help with the math to calculate Torque to the rear wheels if you know the gear ratio's, but a quick approximation would be to take motor HP and subtract around 10% to give you the HP at the tires. Regards

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tej
On my B-12 I have a 12HP briggs engine. The engine is rated by Briggs to be 12HP at the flywheel. The power is transmitted to the wheels though a series of pulleys and gears resulting in gearing the tractor down to travel at low speeds and have power to pull. Farm tractors use to be rated on draw-bar horse power and PTO horse power. On any tractor the draw-bar horse power should be higher than the engine horse power because of the gearing. So what's the draw-bar horse power of my B-12?

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Kent
Good response from Arnold. Also keep in mind the old rule of measure of horsepower. 1hp= the ability to lift 2000 lbs 1 foot in one minute. Now consider 12 horses in front of your tractor pulling a plow. Suddenly horsepower is not as big of an issue as we think. Doing the kind of work that a tractor does takes torque, and lots of it. The gear reduction of the belt pulleys and gear box increase the usable torque well over 100 times. Considering a 12hp engine will develop around 24lb/ft of torque, it is obvious to see what the real power is. Also know that when the horsepower of a tractor is measured at the drawbar, the method used to reach the hp rating is not that much different than the method used in the old days. Only now a draw force gauge is used to determine the total amount of force a tactor can develop using a combination of gear reduction an ample traction.(just because you may have high hp doesn't mean you will have good draw).

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tej
Thanks for the responses. I am aware of the methods for determining HP rating. However when tractors are rated at the drawbar the added torque created by the gearing should increase drawbar HP. Tractors that had both belt HP and drawbar HP had different rating for each as they had different gearing. The belt pulley turning faster than the rear wheels. And yes HP can be over rated as torque is what gets the work done. An engine with a long stroke can have more torque than a higher HP short stroke engine.

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PhilD
Me not being very technically orientated, and a truck driver to boot, I explain it this way: That old 350hp 350cid Chevy engine was pretty impressive about the way it would get that 3,500 lb car moving to 60mph. But try giving that nifty engine an 80,000lb load, with as many gears as you like. It probably would never make that speed (assuming level road), much less do it as fast as the 350(hp) Cummins that many of the heavy trucks still have. The difference is the torque, which is the only thing to go by for pulling power. This "drawbar horsepower" is likely a figure that someone dreamed up a formula using torque to get. Of course, I'd be speculatin :^) *my ten minutes typing worth* DoubleT

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JordB110
Double T is right, the only thing to go by for pulling power is torque. Some modern tractors may only have 180 hp. but over 1300 ft. lbs. of torque! horsepower ratings may be impressive but only if they have the torque to back it up.

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