How to explain Horsepower?

jon

Well-known Member
Just lost a sale on an 8n because he didn't think it would run a bush hog good enough with HP in the mid 20's. (I've read 25-27?) He said his lawn mower is 18 hp & it won't cut it.
How do you explain the apples to oranges scenario here?
 
Good question, I bet some interesting answers.
First, I do about 12 acres, my 8N is certainly up to bush hogging it, even with the grass FAR higher than any "lawnmower" could handle, 3 feet or so.

My guess would be the transmission gear reduction to the wheels effectively amplifies the power.
Ever see a lawn mower with tires as big as an N's ?
 
First, I do about 12 acres, my 8N is certainly up to bush hogging it, even with the grass FAR higher than any "lawnmower" could handle, 3 feet or so.
Forgot to add, his [i:a5de4c82d2]source[/i:a5de4c82d2] said it wouldn't run anything over a 4 footer! :roll:
 
I saw it to-nite That 5ft'er takes on all comers... Some poor SOB is not gonna like what it tears up....
Now that's a lotta bush hog for not much tractor! :D
 
NO explanation needed. You are so lucky you "lost the sale" as the guy would have been after you FOREVER, for one thing or another, had he bought it.

Someone who knows what an 8N is will come along and buy it soon without all the snarky BS.
 
Bring him and his 18 hp lawnmower to my property and we'll show him how an old 8n can eat his lunch.
 
"You are so lucky you "lost the sale"...."

That's what I was thinking too. Dude might even kill himself.
Just think about trying to explain why he would need an ORC.
Not that he couldn't understand, but his "source" would say otherwise.
 
Now days HP is based on RPM where as when those old tractor where built HP was based on torque power so yep saying a lawn mower has more power it like comparing a big rock to a big tree. Neither one has to do with the other.
 
You are so lucky you "lost the sale" as the guy would have been after you FOREVER, for one thing or another, had he bought it.
I'd say you're right Bob. I think the 6 volt worried him even tho I told him about it starting easily in 18° weather last week.
 
(quoted from post at 18:10:17 11/23/14) Just lost a sale on an 8n because he didn't think it would run a bush hog good enough with HP in the mid 20's. (I've read 25-27?) He said his lawn mower is 18 hp & it won't cut it.
How do you explain the apples to oranges scenario here?
orsepower is a measurement of what they call in the physics world 'Work'. Work is the application of a force over a time and distance. You want more horsepower you just have to increase your time and distance metric and keep the same force.

The true GRUNT of an engine isn't it's horsepower but it's torque. Torque is the force the engine puts out like others mentioned above. Torque is force metric that is put out at it's max potential. A good way to think of it is imagine you have a really stuck bolt and you can't bust it loose. Well, we've all grabbed a cheater pipe and put it over a breaker bar/ratchet to break loose a bolt. If you are a 150 lbs person and you place your full weight on a 1 foot long ratchet you are exerting 150 ft/lbs of force. If you grab a 2 foot long cheater bar and then put all your weight into it you are then putting out 300 ft/lbs of force.

Just like with busting bolts/nuts loose, torque is what gets the really tough work done.

Food for thought, our little N's put out about 250 ft/lbs of torque on the PTO shaft. A 25 hp lawn mower is only going to have about 45 ft lbs of torque given they have to get everything spinning up around 3000-3500 rpms to get 25 horsepower out of it. There is no comparison.
 
(quoted from post at 21:10:17 11/23/14) Just lost a sale on an 8n because he didn't think it would run a bush hog good enough with HP in the mid 20's. (I've read 25-27?) He said his lawn mower is 18 hp & it won't cut it.
How do you explain the apples to oranges scenario here?

Rotary Mower HP 101:

The lawn tractor spins the blades through either a direct or step up belt drive (3600+ blade RPM) which actually decreases the engine torque delivered to the mower blades. The tractor PTO and bush hog gear box is a speed reduction drive (540 blade RPM) which increases the torque delivered to the mower blades.

Delivering more torque to the mower means you can cut wider and/or heavier growth with the same HP/torque engine. Lower blade speed means a more ragged finish to the cut.

(quoted from post at 23:30:01 11/23/14) The 8n is rated @ 2000 rpm , if it were rated at 3600 rpm , with no muffler or air filter I would guess 45 hp would be close .

At 2000 rpm the 8n probably has 5 times the torque that a briggs has @ 3600 .

http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm

Pretty close. Here are the power and torque curves for the L-head. Maximum dynamometer HP is 42 BHP @3000 RPM. Maximum dynamometer torque is 90 lb-ft @ 1600 RPM.

TOH

L-HeadPowerCurves-2.jpg
 
(quoted from post at 23:04:18 11/23/14) Now days HP is based on RPM where as when those old tractor where built HP was based on torque power so yep saying a lawn mower has more power it like comparing a big rock to a big tree. Neither one has to do with the other.

No. The mathematical relationship of mechanical HP to torque and RPM, has not changed since James Watt first devised the unit of measurement ca.1750:

1 hp ≡ 33,000 ft-lb/min

TOH
 
Them lawnmowers use small horses!

Lawnmower engine ratings are about as valid as anything a politician says.

Deceptive tactics, like lab test engines running special fuel, different carb settings, no accessories, and rpm tested for hp calc rich before engine detonates
 
An easy,uncomplicated answer is that with an N tractor,the horsepower is net HP. With a lawn tractor,mower,car,etc,it's gross HP. The net HP is what you actually have available to you for work,while the gross HP is only what the manufacturer says the Motor has. I saw tests on popular cars in the '70s,and some of the cars had motors which claimed 225Hp.but only delivered 45-50 at the rear wheel.My old '41 9n powers a 5' hog very well,and cuts grass and saplings that you have trouble walking through.
 
(quoted from post at 10:44:07 11/24/14) Them lawnmowers use small horses!

Lawnmower engine ratings are about as valid as anything a politician says.

Deceptive tactics, like lab test engines running special fuel, different carb settings, no accessories, and rpm tested for hp calc rich before engine detonates

OEM engine HP ratings are only as trustworthy as the rater and the method of measurement used. Lots of variables can affect the measurement. Here are some examples of different types of ratings and how they are measured from Wiki. The emphasiswas added by me:

[i:4367e60d28][Tb][u:4367e60d28]he power of an engine may be measured or estimated at several points in the transmission of the power from its generation to its application. A number of names are used for the power developed at various stages in this process, but none is a clear indicator of either the measurement system or definition used. [/u:4367e60d28][/b]

In the case of an engine dynamometer, power is measured at the engine's flywheel.[citation needed] With a chassis dynamometer or rolling road, power output is measured at the driving wheels. This accounts for the significant power loss through the drive train.

In general:

Nominal is derived from the size of the engine and the piston speed and is only accurate at a pressure of 48 kPa (7 psi).[24]

Indicated or gross horsepower (theoretical capability of the engine) [ PLAN/ 33000]

minus frictional losses within the engine (bearing drag, rod and crankshaft windage losses, oil film drag, etc.), equals
Brake / net / crankshaft horsepower (power delivered directly to and measured at the engine's crankshaft)

minus frictional losses in the transmission (bearings, gears, oil drag, windage, etc.), equals
Shaft horsepower (power delivered to and measured at the output shaft of the transmission, when present in the system)

minus frictional losses in the universal joint/s, differential, wheel bearings, tire and chain, (if present), equals
Effective, True (thp) or commonly referred to as wheel horsepower (whp)

[b:4367e60d28][u:4367e60d28]All the above assumes that no power inflation factors have been applied to any of the readings.[/u:4367e60d28][/b:4367e60d28][/i:4367e60d28]

TOH
 
(quoted from post at 11:10:49 11/24/14) An easy,uncomplicated answer is that with an N tractor,the horsepower is net HP. With a lawn tractor,mower,car,etc,it's gross HP. The net HP is what you actually have available to you for work,while the gross HP is only what the manufacturer says the Motor has. I saw tests on popular cars in the '70s,and some of the cars had motors which claimed 225Hp.but only delivered 45-50 at the rear wheel.My old '41 9n powers a 5' hog very well,and cuts grass and saplings that you have trouble walking through.

The easy uncomplicated answer is it depends on where and how you do the measurement. Which 8N horsepower number do you like?

Ford claimed 30 engine BHP at 2400 RPM on a dynamometer running at 80% full load.

The various Nebraska power test runs with actual tractors produced a number of different "net" horsepower ratings for the 8N:

Belt Horsepower = 21.06 to 25.77
PTO Horsepower = 18.35
Drawbar HP = 18.79 to 21.95

TOH
 
and outside the realm of hp, you have to look at tire size, stall and spin. A 17hp lawnmower with low weight, small tires. and reduced traction tires rolling up to a sapplin will likely stall movement and spin tires. yet my 12 hp IH cub can roll right over
 
I have to disagree with you since if you compare a 24HP lawn more to the 8N the lawn mower does not come close as for TRUE HP
 
(quoted from post at 12:34:42 11/24/14) I have to disagree with you since if you compare a 24HP lawn more to the 8N the lawn mower does not come close as for TRUE HP

You can disagree all you want but you will still be wrong. This is not a matter of opinion - it is physics.

In the 18th century an engineer named James Watt proposed a new unit of measurement for power (work x time) in order to compare the amount of work a new fangled invention called a steam engine couid produce to the amount of work produced by the commonly used draft horse. His definition for this unit of power measurement was EXACTLY the one I gave you earlier:

1 horse power = 33,000 lb/ft per minute.

That is torque x time = power and has been and still is the definition of mechanical hose power used by engineers since 1750.

If you do not understand why a modern lawn tractor engine running at 3600 RPM is producing the same [b:a3bd64e83b]TRUE[/b:a3bd64e83b] engine horsepower as the L-head in an 8N tractor running at 2000 RPM you need to brush up on your physics.

TOH
 
I understand the physics part of it but there is no way a 24 hp lawn mower engine produces more HP then the 8N engine does no way in the world it can do so.
 
(quoted from post at 13:11:43 11/24/14) I understand the physics part of it but there is no way a 24 hp lawn mower engine produces more HP then the 8N engine does no way in the world it can do so.

Then you don't understand the physics.

TOH
 
Yes I do but there is no way you could have that 24 hp lawn mower engine if it could be done work as the engine of an 8N work
 
(quoted from post at 15:25:32 11/24/14)
(quoted from post at 10:16:45 11/24/14) Yes I do but there is no way you could have that 24 hp lawn mower engine if it could be done work as the engine of an 8N work

Here's how Gus Wilson answered the question: What Horsepower Really Is

es

I think it is enlightening that we are still having this lack of understanding in 2014. We have grown up in a world were engines of all sorts are an intimate part of everyday life.

I can only imagine the frustration James Watt must have felt in 1750 trying to explain rotary engine power to a bunch of poorly educated farmers, tradesmen, and factory managers with minimal if any mathematical skills. The concept of an "engine" was totally foreign to them and their only concept of power was embodied in a 2000+ pound draft animal that either pulled or carried a load while plodding along at the speed of smell. Fortunately they were open minded and smart enough to try and grasp the engine power concept else we would still be traveling overland on stagecoaches and using mulles to pull barges loaded with goods along canals.....

TOH
 
Horsepower for a rotating shaft, engine in this case is:

HP = {Torque(Lb-ft) X RPM} / 5252

Your 8N generates a lot of torque but at a relatively low RPM. That's why the HP numbers are fairly low. But when we're talking tractors, torque is what gets the job done.
 
(quoted from post at 19:32:21 11/24/14) Horsepower for a rotating shaft, engine in this case is:

HP = {Torque(Lb-ft) X RPM} / 5252

Your 8N generates a lot of torque but at a relatively low RPM. That's why the HP numbers are fairly low. But when we're talking tractors, torque is what gets the job done.
ut....looking at your equation, you can trade torque for rpm or rpm for torque with simple gears.....still all the same hp, less of course a couple of percent gear loss.
 
(quoted from post at 19:46:37 11/24/14)
(quoted from post at 19:32:21 11/24/14) Horsepower for a rotating shaft, engine in this case is:

HP = {Torque(Lb-ft) X RPM} / 5252

Your 8N generates a lot of torque but at a relatively low RPM. That's why the HP numbers are fairly low. But when we're talking tractors, torque is what gets the job done.
ut....looking at your equation, you can trade torque for rpm or rpm for torque with simple gears.....still all the same hp, less of course a couple of percent gear loss.

Everybody knows that!!! But did you know that 15 minutes could save you 15% on car insurance.

I wondered how far it would have to go before you jumped in ;-)

TOH
 
1 Horse power is the amount of energy it requires
to lift 100 pounds 1 foot in 1 minute.

Zane
 
(quoted from post at 20:15:40 11/24/14) 1 Horse power is the amount of energy it requires
to lift 100 pounds 1 foot in 1 minute.

Zane

Make that 33000 pounds in one minute and you would be right.

From the online lecture notes for GS321 (General Science) at Western Oregon University:

[i:92c8837fb4]To promote his steam engines, James Watt compared the amount of work an engine could do to the common power source of the late 1700s, the horse. One horsepower (hp) was defined as the amount of work a horse does to lift a 33,000 pound weight a distance of one foot in one minute. This may seem like an odd definition, but it was based on the work a horse did hauling coal (Watt was trying to encourage the use of steam engines in coal mining).

1 hp = 33,000 foot-pounds (ft/lb)/min

A horse moving 33,000 pounds of coal a distance of one foot; one moving 330 pounds a distance of 100 feet; or another moving 33 pounds 1,000 feet in a minute are all exerting the same power.[/i:92c8837fb4]

That is equivalent to lifting 550 pounds 1 foot in one [u:92c8837fb4]second[/u:92c8837fb4] (550 x 60 = 33000) - another way to define 1 HP.

TOH

5416972.jpg
 
I did this write-up for another forum several years ago.

Everyone has provided a lot of great info about horsepower and torque,
but nothing as where it is derived from in an engine.
It's actually quite simple. From a 19th century steam engine book:

Horsepower = PLAN/33000

P = Pressure (Mean Effective Pressure, MEP)
L = Length of Stroke
A = Surface Area of Face of Piston
N = Number of (Power Strokes) per minute

The formula may have originally been for steam engines
but it also works for internal combustion engines.

Some additional info:
Mean Effective Pressure (MEP).
At the top of the stroke a pressurized gas is introduced into the cylinder.
The pressurized gas can be steam, or it can be pressurized by sealing an
air/fuel mixture in the cylinder and igniting it. If steam is used, a valve is
opened momentarily to admit steam, then closed. The steam pushes the
piston and expands the volume of the cylinder. The piston pushes the
crank rod which pushes the crank which rotates because of the torque
produced by the crank angle and the force of the crank rod.
If an air/fuel mixture is used in an internal combustion engine the same thing
happens but the pressure is generated inside the cylinder by the burning
fuel. I'll get to flame speed in a bit as it relates to gas or diesel engines.
If you inject 100psi steam into a cylinder and then close the valve, the
piston will move and the volume inside the cylinder will increase. As the
volume increases the pressure will drop. MEP is sort of an average pressure
as the piston moves from the top to the bottom. MEP is also affected by
the crank angle as the crank rotates it changes the moment arm between
the crank rod and the crank shaft. This also affects torque in the stroke.
It is the same thing in an I.C engine. The fuel ignites and expands to create
pressure. Then this pressure does the work the same as in a steam engine.
Now this is also where flame speed comes in. Someone once said that time
is nature's way of keeping everything from happening at once. This is so true
in the timing of an engine. Everything has to happen in its proper time.
In a steam engine, the crank reaches top dead center (TDC) and a valve
opens to admit steam. But even as the steam is being admitted the piston
is already moving down the shaft increasing the volume. If steam is
admitted at a rate so that the MEP is constant thru the stroke then the only
H.P and Torque being created is being used to overcome friction losses.
You have to admit steam fast enough to keep cylinder pressure up so that
there will be extra H.P and Torque to do useful work from the engine.
In I.C engines where the pressure is generated inside of the cylinder
The fuel will burn at a certain rate (flame speed) until it is consumed.
As it burns the gaseos vapors will be expanding (creating pressure) and
the piston will be moving down the cylinder. When the fuel is consumed the
resulting gaseous vapor will be at its maximum volume and the rest is up to
MEP in the cylinder. Gasoline has a high flame speed so most of the
combustion takes place at the top of the stroke where the moment arm is
smallest. The rest of the stroke is dependant on MEP so torque is lower and
must be produced at higher RPMs burning more fuel. With diesel engines the
flame speed is slower and the pressure is generated thru a great portion of
the stroke. At half stroke the moment arm is greatest and the most torque is
produced. Because of the slower flame speed the torque curve is shifted into
this section of the stroke giving the diesel engine a higher torque rating and
at a lower RPM, making it more fuel efficient.

Horsepower is a unit in the English Standard system and is defined as
33000 foot-pounds per minute, or 550 foot-pounds per second.
Any permutation of these numbers can be used. 1100 ft-lbs/sec = two H.P.
15500 foot-pounds per 30 seconds = one horse power.

It is a derived unit based on amount of work done per unit of time.
Around 1780 James Watt defined the unit arbitrarily by watching horses
power a water pump. Four horses were hitched to a device that walked
them in a circular path. Their walking rotated the device and the rotative
energy was used to lift water from a deep well. Watt studied this process
and kept notes of the volume of water lifted and the speed of the horses.
From this data he calculated one average horse could lift 33000 pounds of
water a distance of one foot in one minute. Or 550 pounds in one second.

Since it is a unit of power per unit time it can be converted to other similar
units. It may sound strange to hear it but my 23hp 8N tractor could also be
said to be a 17151.097 watt 8N tractor. A 200 watt light bulb =
.268204418 horsepower. And one HP = 745.699872 watts.
A watt is a unit in the S.I system (metric) named in honor of James Watt.
Units of power can also be expressed as joules per second, or it can be
(((kilogram*meter/second^2))*meter)/minute, or newton*meter/second, etc.

And horsepower don't mean nothing if you can't put it to the ground.
You can have 3000HP but if you just sit there and spin your tires in the mud
then it don't mean anything. Putting the power to work is what counts.
You can put your power in traction, or operating a hay baler, or brush hog,
or basically anything that requires energy input to recieve a desired action.
How you can use it is what counts. Just like the man that couldn't pull the
heavy boat out of his barn with the 300 hp truck, but the 20 hp tractor
could do it, it's all in how you put the power to use.

And the reason you see the inflated HP ratings on things today is horsepower
sells tractors. Salesmen are counting on you to not know what it means.
Then you get into real horsepower vs developed horsepower.
Developed HP is an imaginary number and basically be ignored.
It's what you can actually use that is what counts.

Pooh Bear (aka Fluff for Brains)
 
Well I could not go to that site due to dial up but yes few understand HP and torque power and how RPMs can add HP but not add torque power and all in all not all things are as simple or add up when the work has to be done
 
(quoted from post at 22:47:13 11/24/14) Well I could not go to that site due to dial up but yes few understand HP and torque power and how RPMs can add HP but not add torque power and all in all not all things are as simple or add up when the work has to be done

And even fewer understand why physics defines

work = force x distance

and

power = work x time = force x distance x time.

A horse carrying a 330 pound load 100 ft does 33,000 pound-feet of work. If it takes the horse 1 minute to do that work the horse expends 1 full horse power of energy doing the work. If the horse does it in 2 minutes the horse expends 1/2 horsepower of energy doing the same work....

When you understand what that means in real life to the horse or an engine performing that work you will truly comprehend why and how physics differentiates power from work.

TOH
 
(quoted from post at 23:07:37 11/24/14)
(quoted from post at 15:25:32 11/24/14)
(quoted from post at 10:16:45 11/24/14) Yes I do but there is no way you could have that 24 hp lawn mower engine if it could be done work as the engine of an 8N work

Here's how Gus Wilson answered the question: What Horsepower Really Is

es

Here's a video representation if you haven't seen it.
I find it quite funny! YouTube

I think that is Gus' explanation of traction versus torque ;-)

TOH
 
Speaking of James Watt........

Saw the 1788 engine in Munich a couple of weeks ago; that's the picture.

The link is to a YouTube video showing it in operation.
IMG_20141117_105019_723_zps20e9baec.jpg

Watts Engine
 
(quoted from post at 19:53:47 11/25/14) @Pooh Bear, hey nice to see someone on here a little closer to home.

Used to be another one of us down in the Suck Creek area.
Maybe we'll meet up some day.
 
I think I learned something here. It has been quite some time since I sat in a classroom and learned all about Horsepower and torque and I would like to thank you guys for getting into this discussion. Answered some questions that I had forgotten and opened my mind to seeing a few different points of view.

jeff
 
Most lawn mowers use a belt drive and in my experience, when the going gets tough, the belt slips. Horsepower is horsepower. Most laen mower engies are rated at 3600 rpm so they need to be "geared down" by pulleys to a lower rpm. The torque multiplication that occurs from this must be able to be transmitted by the lawn mower drive belts.

Certainly an 18 HP tractor with a pto driven mower will be able to apply it"s torque to bush hog blade better than an 18 HP lawn tractor with a belt drive will be able to do.
 

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