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  1. #1
    Silver Member Harvster's Avatar
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    Kubota B7610

    Default edumacate me on horse power

    This has been bugging me a bit so I just know there is a simple answer.

    How is it that tractors with 20 or 30 horsepower can do so much lifting, pulling etc, while a typical four door sedan often has 200+ horsepower and seems so useless and wimpy in comparison. Obviously the car is designed more for speed and acceleration, but is it really just the gearing and some hydraulics that transform something with 1/10 the horsepower into such a useful machine?

  2. #2
    Super Member N80's Avatar
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    Kubota L4400 4wd w/LA 703 FEL

    Default Re: edumacate me on horse power

    Gearing and torque. Cars have high hp ratings but if you look at 'where' the hp is made it is at really high rpms, rpms that most of us don't usually hit or spend much time at. Also, you will notice at such high rpms the torque has fallen off quite a bit. Also, most cars cite hp ratings at the flywheel, nowhere near that much hp makes it to the rear wheels. This is a marketing thing. The tractor makers may do the same, but the number you see for cars is usually inflated and fairly meaningless. Tractor engines are design for low rpm torque and hp and you add low, low gearing and big sticky tires and you get a machine that can do a lot of low speed work. Obviously such a vehicle is useless for cruising down the interstate.

    But when people who don't know anything about tractors hear tractor people talking about 45, 70 or even 100 hp they typically think, gee, my Hyundai or my outboard boat motor makes more hp than that! Little do they know...
    George
    South Carolina

    "What is truth?" Pontius Pilate

  3. #3
    Bronze Member
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    North Alabama
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    Kubota L4630

    Default Re: edumacate me on horse power

    Like was said, gearing and torque..and add in traction. Low, LOW gearing, (top speeds on a tractor will be in the teens to low 20 MPH), CUTs often weight as much as a 1/2 ton truck and have deep lugged tires so it's rare they spin. They dig in and PULL.

    Also the diesel engines used in tractors make all their power at low RPM's. I used to think the same thing about the power differences but once you hook a tractor to something and put it in low gear, it's a real rush to feel the power working.

    I've got a 18 HP gas lawn tractor (lawn mower) with a 46" cut. It struggles through some high grass near my barn. My 46 hp 'bota will pull a 72" bushhog through the same grass and literally never know it's there.

  4. #4
    Elite Member Dmace's Avatar
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    Default Re: edumacate me on horse power

    The big difference is the fact that the 20-30 hp tractors are Diesel as opposed to 200 hp gas burning cars.

    Diesel has a lot of oil in it. When it is ignited (by high compression air) it burns as opposed to gasoline that just flash burns when ignited (by a spark). The difference is the slow burn of the diesel pushes the pistion all the way down the cylinder and continues to push that cylinder down, this is why there is so much torque out of a diesel. When a gasoline engine ingites in a cylinder, there is a quick flash bang that hits the piston and sends it downwards but does not continue to push the cylinder down.

    Have I lost you yet?

    This is also why you can put so much load on a diesel engine. The pistons are always getting pushed down, whereas on a gas engine any load on the engine will slow it down considerably since there is no constant force downward on the piston. That is why they need high rpms to make power.
    Derek
    Kioti CK20HST
    KL120 FEL // KB2365 BH // 60" JRW 3ph snowblower // 48" HD Boxblade
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    Quote Originally Posted by DiamondPilot
    Now it's time for Ford and GM to step up

  5. #5
    Super Member flusher's Avatar
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    Getting old. Sold the ranch. Sold the tractors. Moved back to the city.

    Default Re: edumacate me on horse power

    Quote Originally Posted by Harvster
    This has been bugging me a bit so I just know there is a simple answer.

    How is it that tractors with 20 or 30 horsepower can do so much lifting, pulling etc, while a typical four door sedan often has 200+ horsepower and seems so useless and wimpy in comparison. Obviously the car is designed more for speed and acceleration, but is it really just the gearing and some hydraulics that transform something with 1/10 the horsepower into such a useful machine?
    A more relevant comparison might involve something like my 21-hp (engine) kubota B7510HST tractor with an LA302 FEL (4-ft wide bucket), my Huskee riding mower with an 18-hp B&S engine and my neighbor's 4-wheel Honda ATV with a ~500cc engine (don't know the hp).

    The 7510 has typical tractor implements available around my place: 4-ft brush hog, 4-ft box blade, middle buster/subsoiler, 4-ft rototiller. Can get lotsa work done with these.

    I can pull a lightweight drag, a lawn roller weighing about 200 lb and a small drop seeder with the Huskee and that's about all.

    I see my neighbor using his ATV to pull a lightweight spike drag and I know you can get other implements for an ATV like a small disk harrow, seeder, etc. But without hydraulics and a pto, the ATV is fairly limited for farm work. The most common use around here for the ATV is for transportation in the large olive orchards, usually to check the irrigation system and to plink ground squirrels.

    Without the 7510's hydraulics for the FEL and 3pt and the rear and mid ptos, the Huskee and the ATV come up short for heavy duty work around the farm.

  6. #6
    Platinum Member herringchoker's Avatar
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    Default Re: edumacate me on horse power

    Horsepower is a contrived measurement. 1 horsepower equals 33,000 foot-pounds per minute. That means 1 HP could be the movement of 33,000 lbs. a distance of 1 foot in 1 minute, or moving 1 lb. a distance of 33,000 ft. in 1 minute, or anything in between. Moving a light weight real fast or moving a heavy weight real slow can result in equal horsepower ratings. In that way, comparing horsepower ratings can be like comparing apples and oranges.
    Kubota B7800, LA402 FEL, Homemade cab, 60" bushcutter, 74" rear snowblower (shrunk to 62").
    Kubota RTV500.
    Case 450 c/w 6-way dozer.

  7. #7
    Super Star Member
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    JD2010, Kubota3450,2550, Mahindra 7520 w FEL w Skid Steer QC w/Tilt Tatch, & BH, BX1500

    Default Re: edumacate me on horse power

    Quote Originally Posted by herringchoker
    Horsepower is a contrived measurement. 1 horsepower equals 33,000 foot-pounds per minute. That means 1 HP could be the movement of 33,000 lbs. a distance of 1 foot in 1 minute, or moving 1 lb. a distance of 33,000 ft. in 1 minute, or anything in between. Moving a light weight real fast or moving a heavy weight real slow can result in equal horsepower ratings. In that way, comparing horsepower ratings can be like comparing apples and oranges.
    That would be raising 33k# a foot a minute. Power is Force X Distance/Time. The Force applied must be 33k#.
    The reason diesels are so much more suitable on tractors is their natural accommodation of varying loads without operator input to shift gears. This stems from the extremely high compression ratio and the comparatively slow combustion. These factors couple together to cause a diesel to produce more torque [Force] as it slows below its peak HP rpm [Distance/Time]. So, with engine force rising as rpms drop, the power product on a diesel can remain very near constant as it slows. This means it remains capable of doing Work at the same rate. --But the load you are pulling with your tractor very seldom becomes harder to pull as you slow. Usually it remains the same or decreases. So Force exerted by the tractor is the same or less, and its speed [Distance/Time] is less. The required HP product has decreased while the available engine HP product has remained the same. Its like having a continuously variable transmission inherent in the engine tractability. Indeed, the diesel advantage would disappear on equal HP Gas and Diesel powered HSTs if only wheel HP were in use. -But the advantage would resume as soon as PTO was engaged.
    Larry

  8. #8
    Veteran Member
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    Default Re: edumacate me on horse power

    It was hard to convince my brother to let me pull his boat either in or out my barn when the ground is soft until his 6000# 300hp 4wd chevy got stuck. He unhooked the 6000# boat and trailer allowing him to drive off and i hooked up my 4000# 33hp tractor and crept right out. That had the most to do with traction.

  9. #9
    Platinum Member
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    20 miles southeeast of downtown Sacramento
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    Default Re: edumacate me on horse power

    HP is HP. It really doesn’t matter if it is gas, diesel, steam, electric, air, or hydraulic powered (some may last longer, use less fuel need different gearing). But yes it really is just the gearing, hydraulics, weight and traction that transform something with 1/10 the horsepower into such a useful machine. Of course it won’t get a family of four down the freeway at 70mph and that freeway merge is pretty tough. But then again that hemi would tear the guts out of most any tractor out there.
    Kubota BX23, BT600 BH, LA210 FEL, Maschio L125 tiller, Gearmore BB 20-48 BB, King Cutter 6' rear blade, Homemade PHD, Brinly BST-50 broadcaster, ? 6' cultipacker, log & chain drag.

  10. #10
    Elite Member Dmace's Avatar
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    Default Re: edumacate me on horse power

    Quote Originally Posted by bx23barry
    HP is HP. It really doesn’t matter if it is gas, diesel, steam, electric, air, or hydraulic powered
    So you are saying, I could put a 21 hp gas engine in my tractor with the same gearing and same hydraulics with no difference in work produced?

    I don't think so!

    Yes HP is HP, it's just a number. The difference is how the HP is made. Which is stronger ?, something hitting a 33,000lb object up 1ft over a period of 1 min or something pushing 33,000lb all the way up to 1ft in the same 1 min.

    Here is a link about where the formula came from.
    What is Horsepower?
    Derek
    Kioti CK20HST
    KL120 FEL // KB2365 BH // 60" JRW 3ph snowblower // 48" HD Boxblade
    Sims-Cab Depot heated cab
    Quote Originally Posted by DiamondPilot
    Now it's time for Ford and GM to step up

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