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Demystifying (for me) torque and horesepower

F

flyingace

Member
I'm of the theory that HP is a terrible measure of the work a tractor can actually do. I base that on the fact that there are motorcycle engines of 1000cc (60 CID) that make 120 HP. They do this by having relatively little torque and spinning the engine at about 12K. This rapid RPM multiplies the smallish torque into the large HP number.

My question is, would there be any way to make this fast spinning little engine do the work of a 120 HP tractor? A 50 HP tractor? If not, why not?
 
Ft lbs x rpm/5252 =Horsepower. In answer to your
question in theory yes, in practice no. You can
use a smaller engine turning at more RPM and gear
it down to get torque but the gearing to reduce
the speed has some parasitic loss, you go to small
and the gearbox eats all of your power. If you
want to see how this has been applied look at farm
tractors from the late 40's early 50's and compare
them to the tractors of the late 50's early 60's
FROM THE SAME MANUFACTURER, you'll see in many
cases engines that are the same size and
remarkable similar to the earlier engines putting
out more power by simply turning faster, or in the
case of John Deere large 2 cylinder engines that
from the letter (A,B,G and R) to the first number
series (50,60,70 and 80) get slightly smaller in
displacement with a bump in RPMs, the next number
series (520,620,720,and 820) more rpms, last 2
cylinder series (530,630,730 and 830) not much
power change other tractor changes meant more work
or more comfort, then look at the new generation
tractors (2010,3010,4010) Smaller engines with
more cylinders turning faster. The folks at IH did
kind of the same thing the H sized tractor in the
number series grew into a three plow tractor, The
M sized tractor into a 4 or 5 plow tractor
 
Horsepower was originally used to measure work horses did. I think it was measuring the time to perform a vertical lift of a measured amount of material out of a mine.
It was adapted to mechanical engines. You are correct the operator "feels" the power. The reason small motorcycle engines seem powerful is because they turn very high RPM's and often have 5 or 6 speed engines. In otherwords the engine is producing close to max. power most of the time.
Tractor engines normally lug down to peak torque before it is necessary to downshift. As somebody else said the John Deere two cylinder engines had tons of torque but were low RPM engines. When you go back to the formula of HP = Torque x RPM divided by 5252.
Hope this helps, it is kind of hard to explain this way. A college professor would spend at least a day explaining it.
 
Power is the rate at which work occurs (rate of energy transfer). It is the only measure of the work a tractor or engine can do (over a given amount of time).

A 120hp 1000cc engine can do the same work as a 120hp 5000cc engine in the same amount of time.

Losses in the necessary gear reductions to reduce the speed are about 2% per mesh. A 12,000rpm motorcycle engine can be slowed down to an equivalent speed of a diesel engine with about 2 planetary meshes. This would lead to about a 4% loss that wouldn't be experienced with the larger engine.

In an ag tractor, the shape of the torque curve matters. The shape of the torque curves affects how it can lug through a tough spot without down shifting. If the motorcycle engine had the same general shape torque curve, you might not know what was powering the tractor (other than the sound!). In reality, the torque curve of the motorcycle engine probably doesn't have the rise of an ag tractor engine. I would expect more shifting to make it work.

Of a more practical note, large ag/construction/industrial engines are designed to run at full power for a high percentage of their operation. Automotive and motorcycle engines are not. The 1000cc 120hp engine would not likely last very long at full power.
 

Thanks for the replies. At issue for me is torque. To say a motorcycle engine could pull as much as a JD 'R' just seems ludicrous, even if you could negate the gearing loss. The JD has much more twisting power than the MC engine no matter what RPM the MC engine turns. HP is a measure of work, not force. I found this quote on another forum and it makes the most sense to me:

Torque is how much work CAN be done.

HP is how fast it can get said work done.

Now this makes sense. The motorcycle in no way can pull what a 120 HP tractor can pull, but it it can get the same amount of 'work' done as the
tractor if you reduce the torque requirement so it can spin fast. I think a good analogy is if you hook up both to water wheels. The tractor could lift out massive buckets of water but not at a very fast rate. The MC could lift only small buckets, but at a much faster rate. In the end they would generate the same amount of water.
 
Just where could a "M" sized pull 5 bottoms. Very few place could it even pull 4 unless you only plowed 5in deep or less. There was lots of places they had a hard time pulling three at 6in. Ive plowed a couple thousand A with the "M" pulling 3-14 when it was new
 
460-560, seems I read here somewhere the 560's
were a "5" plow tractor, thought it was a stretch
but the neighbor's 460 with 3-16's plowed faster
then our Super M with 3-14's . The discussion
about narrow torque bands makes sense. I have had
some experience with Ford Fusions with the 4
cylinder and 5 or 6 speed auto transmissions, when
you come off a light hard it's interesting to
watch the transmission keep the engine RPMS up (in
the sweet spot). The comment about automotive
engines not being rated to run wide open is right
on. Tractor engines are more like general aviation
aircraft engines, they produce maximum torque at
lower RPMs. You have to keep the prop speed below
the speed of sound so you can't run the engine
faster unless you add reduction, thus adding
weight and complexity while reducing reliability.
Most automotive engines don't convert well even if
you put a reduction unit on it because they don't
like running at the higher rpms needed to make
maximum power.
 
measured horsepower and torque are the same at 5252 rpm. At less rpm torque is higher than horsepower. At more than 5252 rpm horsepower is higher than torque readings. you can in theory have all kinds of torque but unless work is accomplished there will be no horsepower.Paul
 
(quoted from post at 20:23:19 03/01/12)
Thanks for the replies. At issue for me is torque. To say a motorcycle engine could pull as much as a JD 'R' just seems ludicrous, even if you could negate the gearing loss. The JD has much more twisting power than the MC engine no matter what RPM the MC engine turns. HP is a measure of work, not force. I found this quote on another forum and it makes the most sense to me:

Torque is how much work CAN be done.

HP is how fast it can get said work done.

Now this makes sense. The motorcycle in no way can pull what a 120 HP tractor can pull, but it it can get the same amount of 'work' done as the
tractor if you reduce the torque requirement so it can spin fast. I think a good analogy is if you hook up both to water wheels. The tractor could lift out massive buckets of water but not at a very fast rate. The MC could lift only small buckets, but at a much faster rate. In the end they would generate the same amount of water.
Click to expand...
One horsepower will lift 550 pounds, one foot, in one second. Doesn't matter if done by a horse, a 12,000 rpm engine, a 400 rpm engine, or a piston receiving a pressurized column of water from up the mountain. HP = HP and HP = torque X rpm/5252. Simple physics coupled with James Watt's (1736-1819) definition (measured with actual horses) of HP.
 
Gene,

Wisbaker may have been talking about how the M chassis got different engines with more rpm's and more horsepower from about the same displacement as it evolved into the Super M, the 400, the 450, the 560 and 660 tractors.

Are the 656, 666 and 686 tractors further updates of the M chassis or was the 656 a completely new design like the 706 line was?
 
The 656. 666. and 686 are actually remakes of the 460. Improvements in bearings made it possible to use the smaller and lighter drivetrain of the 460 with the 282 Diesel and 263 gas engines.
 
(quoted from post at 13:02:07 03/01/12) I'm of the theory that HP is a terrible measure of the work a tractor can actually do. I base that on the fact that there are motorcycle engines of 1000cc (60 CID) that make 120 HP. They do this by having relatively little torque and spinning the engine at about 12K. This rapid RPM multiplies the smallish torque into the large HP number.

My question is, would there be any way to make this fast spinning little engine do the work of a 120 HP tractor? A 50 HP tractor? If not, why not?
Click to expand...

Work does not have a unit of time associated with it. A 120 HP tractor or a 50 HP tractor can both plow a 100 acre field. The amount work that each tractor does is the same and is equal to the force required to pull the plow times the distance required to cover the 100 acres. The answer to your question is yes - actually most anything could do the work of a 120 HP tractor if given enough time.

Power as in HP is a much better measure of tractor performance since power has a unit of time associated with it. Power is defined as work performed per unit time and this is why a 120 HP tractor can plow the 100 acres in less time than the 50 HP tractor.

Allow me to reword your question: Can a small low torque high revving engine pull a plow as fast as a high torque low revving tractor engine if they have similar HP ratings. The answer to this question is also yes.

Ok.... now the hard part, to explain the answer: We want to know if we swapped engines in a tractor could we still plow the same amount of acres in the same amount of time. To do this lets assume we want to plow at 4 MPH and that the rear tires do not slip. Therefore, the tractor engine combinations have to develop the same drawbar pull at 4 MPH to plow the 100 acres in the same amount of time. Or, the tractor that develops a higher drawbar pull could pull a larger plow and therefore would take less time to complete the plowing. If we assume our tractor has rear tires with a overall diameter of 58", to plow at 4 MPH we will need to select a gear ratio such that the tires rotate at 23.2 RPM. We will also assume that the tractor transmission has the exact ratio we need. Since we assumed the tires do not slip, drawbar pull is proportional to the torque at the rear axle. Therefore, the engine that can send the greatest amount of torque to the rear axle will develop greatest drawbar pull.

I have in front of me the latest issue of Cycle World. The Kawasaki XZ-14 puts out 191.7 HP @ 10,000 RPM as measured at the rear wheel. Maxmum torque is 113.2 ft-lbs @ 7600 RPM however we want the torque at the HP peak which is 100.7 ft-lbs @ 10,000 RPM. To turn the rear tractor tires at 23.2 RPM with the engine at it's HP peak we need a 431:1 (10,000/23.2) gear ratio. The engine torque (100.7 ft-lbs) is multiplied by the gear ratio (431) resulting in 43,402 ft-lbs of torque available at the rear alxe to pull a plow at 4 MPH.

I will leave the rest to you - to compare tractors/engines simply take the engine torque at the HP peak, determine the gear ratio for 4 MPH (or any desired MPH) and multiply the two numbers together. The resulting torque at the rear alxe for a given speed is the bottom line - not engine torque. You will find the engine with the highest HP always wins. Yes, there is some loss in the gear trains but it is not significant to what we are doing here.

What we are doing is comparing the tractors drawbar power. Power is work per unit time - the tractor with the highest drawbar power can do the most work in the shortest amount of time.

Sorry this got so long - hope it helps. Got to go the myple syrup is ready for the bottles.
 
After reading all the posts there is one item not mentioned that purely separates the two engines you mention. Yes they will do the same work , per second , but does the phrase "duty cycle" ring a bell? How long continiously do you suspect that 12000 rpm engine will DO the same work as the 2000 rpm tractor engine? Now we see the diference. Gear down that 12000 rpm engine so it will pull a 20' disc and put it and the tractor beside ea other and that bike engine will be toast in 200' , the tractor will pull it indefinately. So to answer your post...YES HP is a very poor measurement , in and of itself , of the capabilities of a machine , period..
 
hp is a vastly missleading number for measuring the amount of work a engine can do, on the motorcyle engine, no way can it do the work of a 120 hp tractor, s simple demonstration is easily done, take a old 8n ford, rated at 26 hp, hook it to your suburban friends box store super garden tractor also rated at 26 hp, briggs, koler kawasaki, it doesnt mater, [ no cheating by lifting the garden tractor with the fords 3pt hitch now] but in a straight drawbar to drawbar pull, the old ford will make the box store unit look , well, just silly while the ford does weigh 4 or 5 times what the box store mower does, it also has a nice big heavy flywheel in it which produces tourque which is the engines ability to keep twisting under a load, look at anbother, a big block chevy v-8 can be built to make 425 hp pretty easy, my pete also has a caterpiller engine rated at 425 hp, now the chevy is producing around 500 foot/lbs of tourque at 425 hp, the cat dyno'd in with 1,877 ft/lbs, of tourque, obvisouly one engine can do a vast amount of more work than the other even though both are rated as having the same hp, i think that is why the nebraska tractor tests were invented, back in the day, to provide a realistic way farmers can tell just how much work one tractor will actually do over another
 
You bring up a good point about the duty cycle of an engine. (I alluded to that point in my earlier post.) That being said, the OP asked about power as a measure of tractor capability. In that regard, power is still the right measure of power unit capability.

Given similar durabilities, power is the only way to establish the rate of work that a vehicle can do. A 50hp tractor can do work at 1/2 the rate of a 100hp tractor.

Durability is another question.
 
If a motorcycle engine had a simlar power rating as the R, gearing down the motorcycle engine (negating gearing losses) appropriately would indeed get you the SAME torque as the R (after the gear reduction). That is not ludicrous at all.

Torque is NOT a measure of how much work can be done. It is the cross product of a force and a lever arm.

However, your water wheel analogy is a pretty good one.
 
An engine 1/12th the size but running 12 times as fast - has the same cubic inches moving around per second as a much bigger engine running slow. It's a matter of what's practical.
Also a matter of efficiency. A typical HD engine makes its best efficiecy at the peak of the torque curve - often 1600-2000 RPM. Find a way to run it at 6000 RPM and it becomes a dog with fuel use.

I don't see any mystery here.

Older HD engines use to post horsepower as "derated" because they were designed to last long hours at a given power rating. A light duty engine will often post max power that the engine cannot sustain very long.
 
Torque rise is what most people are actually talking about
when they say torque/lugging power or get thinking that a 5HP
electric motor makes more power than a 5 HP gasoline motor.
Compare a two stroke Detroit diesel to a four stroke Cat of the
same HP. The Detroit will up shift through the gears and is still
pullIing hard when it hits the max rpm governor. The Cat as it
approaches redline is falling flat and running out of "pulling
power as volumetric efficiency is rapidly dropping as rpm
increases. The airflow path and cam timing can not fully fill the
cylinders. Take any short cam timed, small port engine and
dyno the rapid drop in torque as it approaches peak HP rpm.
Thus also a very rapid and pronounced torque rise as the
engine is lugged down from peak HP rPms.
 
(quoted from post at 21:45:45 03/01/12)
(quoted from post at 20:23:19 03/01/12)
Thanks for the replies. At issue for me is torque. To say a motorcycle engine could pull as much as a JD 'R' just seems ludicrous, even if you could negate the gearing loss. The JD has much more twisting power than the MC engine no matter what RPM the MC engine turns. HP is a measure of work, not force. I found this quote on another forum and it makes the most sense to me:

Torque is how much work CAN be done.

HP is how fast it can get said work done.

Now this makes sense. The motorcycle in no way can pull what a 120 HP tractor can pull, but it it can get the same amount of 'work' done as the
tractor if you reduce the torque requirement so it can spin fast. I think a good analogy is if you hook up both to water wheels. The tractor could lift out massive buckets of water but not at a very fast rate. The MC could lift only small buckets, but at a much faster rate. In the end they would generate the same amount of water.
Click to expand...
One horsepower will lift 550 pounds, one foot, in one second. Doesn't matter if done by a horse, a 12,000 rpm engine, a 400 rpm engine, or a piston receiving a pressurized column of water from up the mountain. HP = HP and HP = torque X rpm/5252. Simple physics coupled with James Watt's (1736-1819) definition (measured with actual horses) of HP.
Click to expand...
Torque is not work. Work is force over a distance during a known length of time . Power is force over distance.A beam in your barn is holding up tons but it is doing no work because there is no movement. You can hang on the end of a torque wrench pulling 100lbs force for 8 hours but if the wrench hasn't moved, you have done no work.
 
(quoted from post at 08:28:56 03/02/12)
(quoted from post at 21:45:45 03/01/12)
(quoted from post at 20:23:19 03/01/12)
Thanks for the replies. At issue for me is torque. To say a motorcycle engine could pull as much as a JD 'R' just seems ludicrous, even if you could negate the gearing loss. The JD has much more twisting power than the MC engine no matter what RPM the MC engine turns. HP is a measure of work, not force. I found this quote on another forum and it makes the most sense to me:

Torque is how much work CAN be done.

HP is how fast it can get said work done.

Now this makes sense. The motorcycle in no way can pull what a 120 HP tractor can pull, but it it can get the same amount of 'work' done as the
tractor if you reduce the torque requirement so it can spin fast. I think a good analogy is if you hook up both to water wheels. The tractor could lift out massive buckets of water but not at a very fast rate. The MC could lift only small buckets, but at a much faster rate. In the end they would generate the same amount of water.
Click to expand...
One horsepower will lift 550 pounds, one foot, in one second. Doesn't matter if done by a horse, a 12,000 rpm engine, a 400 rpm engine, or a piston receiving a pressurized column of water from up the mountain. HP = HP and HP = torque X rpm/5252. Simple physics coupled with James Watt's (1736-1819) definition (measured with actual horses) of HP.
Click to expand...
Torque is not work. Work is force over a distance during a known length of time . Power is force over distance.A beam in your barn is holding up tons but it is doing no work because there is no movement. You can hang on the end of a torque wrench pulling 100lbs force for 8 hours but if the wrench hasn't moved, you have done no work.
Click to expand...

I think the word 'work' for the first phrase was misapplied. I think a better phrase would have been 'how much force can be applied' then maybe
'how fast that force can be delivered' or something like that.

Now, another question. Torque is a measure of twisting force. What is the
equivalent measure for straight line force? For instance, what unit of measure would you use for describing the force required to pull a plow in
a straight line?
 
(quoted from post at 08:19:16 03/02/12) Torque rise is what most people are actually talking about
when they say torque/lugging power or get thinking that a 5HP
electric motor makes more power than a 5 HP gasoline motor.
Compare a two stroke Detroit diesel to a four stroke Cat of the
same HP. The Detroit will up shift through the gears and is still
pullIing hard when it hits the max rpm governor. The Cat as it
approaches redline is falling flat and running out of "pulling
power as volumetric efficiency is rapidly dropping as rpm
increases. The airflow path and cam timing can not fully fill the
cylinders. Take any short cam timed, small port engine and
dyno the rapid drop in torque as it approaches peak HP rpm.
Thus also a very rapid and pronounced torque rise as the
engine is lugged down from peak HP rPms.
Click to expand...
I`m guessing that in your example of a Detroit Vs. a Cat, you are trying to communicate the difference in the torque curve between the two, as in the cat develops peak torque at a lower RPM, and in a wider band, whereas the detroits torque curve is is much more related to RPM, hence the detroit will accomplish the same amount of work as a cat, through extra revolutions instead of lugging power? Trying to put it in laymans terms, I understand them better. I think the detroit vs. cat is also a good analogy when it comes to understanding why industrial applications usually do not use the smaller, higher RPM motors, even though they can accomplish the same amount of work. A 425 horse detroit can pull as much weight as a 425 horse cat, but most all that have spent time behind both will take the cat over the screamin` jimmy.
 
Perhaps explaining torque rise/ lugging capacity vs an
engine with a flat torque output is via comparing . Some
simplification will be used. Take two othwise identical engines
except one displaces 283cu"and the other 400cu". The
cylinder head ports are small, the cam duration short and are
maxed out supplying the 283 at peak 3000rpm. Max HP of
lets say 150HP and 263 lb ft torque. . Peak torque occurs at
1500 rpm and 400 ft lbs. Exact same everything now
except a 400 cu" bottom end with 1.4 times pumping capacity.
Let's not forget an engine is just an air pump. Will peak HP
at 3000rpm be 1.4 times more ? No because the engine is still
airflow limited. Let's say the choked down 400 still makes the
same 150HP and 263 lb ft of torque at 3000rpm because it's
breathing through a straw. Now let's lugg that 400 down to
1500rpm. Now with the small ports having twice as much time
to fill the cylinders. The 400 can now fill the cylinders full and
make 565 lb ft of torque. Which engine has more rated
power? Neither, they are both 150HP. Which engine has
greater torque rise and lugging capacity? The 400 as it has a
150HP heads and cam with a 210 HP flow capacity bottom
end. The 283 has 150 flow capacity heads/cam with a 150HP
flow capacity bottom end. So by starving the 400's capacity
and the 283 with full airflow capacity. The 400 "feels" more
"Powerful". Seems counter intuitive.
"
 
That is about what I figured you were trying to say, funny how different folks can all be saying the same thing, and nobody understands each other :) On the original posters subject, I would have to say that HP is a good comparison of maximum output of different engines, but torque is what makes an engine seem more powerful anytime it is short of the HP peak, hence why my 700cc two-stroke snowmobile can make 135HP at 8200RPM, and it would certainly make my 4020 move, but if it fell below about 7500, it is gutless, and it would not last nearly as long as the 404ci running at maximum power. Apples to oranges.
 
In theroy you could get the same work from a green leaker. In practice... I rather doubt it. The reason being... you never gain back the time you lost jamming gears at the Jimmy when it falls flat on it's face. They also spend innumberable hours screaming away, burning fuel because they don't have the torque to take a gear and pick up some speed... then lug it out when they hit a tough spot.
I've never seen anything so sad as a 353 to die when it sees a hill.

Rod
 
Horse power is only how fast a specific task can
get done. Pull a hay wagon weighing 2000 pounds
up a 10% grade for one mile in 6 minutes (assumes
full rated power on the engine/motor). It can be
done by any power source with that rated horse
power.
Thus a tiny MC racing engine, or a 2 cylinder JD.
are equal. It certainly requires different
gearing to have it take place, but the power is
equal.
The difference between them will be in the
capability to continue to produce that level of
power output. Unless force fed massive cooling
air, the MC engine would seize. If it made it
(with extra air) it would not do it 20 times in a
row. It is designed to have to make 15 horse
power at 80 MPH for a long time, and 150 HP for 10
seconds at a burst.
The tractor engine can do it for 10,000 hours.
Jim
 
What are you trying to haul with a wee little 3-53 ? They barely made 100HP in the four valve version at 2800 rpm and N45 injectors. Try 100HP engine in any heavy truck. Either a 6V-53 or a 6V-71 is the min with 200 or 240HP.
The two stroke will accelerate better than the four stroke but certainly need down shifting on hills. Tiss the nature of the beast with a flat torque curve.
The DD is always at max torque output. The four stroke has to be lugged down to make the toque output increase.
I've seen numerous DD do just fine on gen sets and in industrial equipment with hydrostat transmissions.Lots of firetrucks still on the road doing just fine with the green leaker too.
 
It's fitted to a 230 TimberJack porter... This one was a blistering 98 hp when it was new. The same basic machine with a 4BT set at 100 hp will outwork it tho.
It's just an application that needs torque rise and the 353 doesn't have it.
Cummins also doesn't burn a gallon or more of oil per day either...
I know one outfit that bought one of these machines with a 353 new... then bought several more Cummins powered machines afterwards... and then changed the first one to a Cummins.
You just lose a lot of time with this thing because it can't lug and it's more expensive to run.
Fire trucks, as you no doubt well know... do not have a great need for torque rise.

Rod
 
That explains a lot, I was thinking of a 2-1/2 ton straight truck application.
A skidder/timberjack with a manual trans would be better suited to just about any four stroke rather than the DD.
I ran an old Terrex 82-30 with the 6-71 DD for a couple of summers.It lacked nothing in pushing power. Of course while wearing ear plugs and ear muffs together.
 
Exactly what I said down below. They will do the same work , but one for 10 min and the other forever."Duty cycle"! Horsepower/torque mean absolutely NOTHING without factoring in duty cycle. Does one want to do a complete rebuild each time across the field with a 100hp motorcycle engine powered tractor or every 15 years with a 4020??
 
This ole hoe has the TJ muffler in front/top of the cab AND a resonator in front of that. One can survive with the muffs alone. It's actually managable at half speed without protection... just not when it's wound up.

Rod
 
(quoted from post at 18:42:44 03/02/12) Horse power is only how fast a specific task can
get done. Pull a hay wagon weighing 2000 pounds
up a 10% grade for one mile in 6 minutes (assumes
full rated power on the engine/motor). It can be
done by any power source with that rated horse
power.
Thus a tiny MC racing engine, or a 2 cylinder JD.
are equal. It certainly requires different
gearing to have it take place, but the power is
equal.
The difference between them will be in the
capability to continue to produce that level of
power output. Unless force fed massive cooling
air, the MC engine would seize. If it made it
(with extra air) it would not do it 20 times in a
row. It is designed to have to make 15 horse
power at 80 MPH for a long time, and 150 HP for 10
seconds at a burst.
The tractor engine can do it for 10,000 hours.
Jim
Click to expand...

See, I don't agree here. In theory, a little electric motor that spins at ridiculously high RPM could make as much HP as a 40 HP JD. Say it has only 1 ft/lb of torque, but spins a 210,000 RPM. According to the formula I used 40 HP = (1 * X) / 5252 where X is RPM. 1 ft/lb of torque will never be enough to pull a plow now matter how fast it spins or how low it's geared, right? I'm guessing this would also be true for any motorcycle engine making 40 Hp.
 
(quoted from post at 16:24:54 03/03/12)

....."See, I don't agree here. In theory, a little electric motor that spins at ridiculously high RPM could make as much HP as a 40 HP JD. Say it has only 1 ft/lb of torque, but spins a 210,000 RPM. According to the formula I used 40 HP = (1 * X) / 5252 where X is RPM. 1 ft/lb of torque will never be enough to pull a plow now matter how fast it spins or how low it's geared, right? I'm guessing this would also be true for any motorcycle engine making 40 Hp".....

The formula is correct and works for low torque and very high RPM. A turboshaft (gas turbine) would be a good example, the turbine spins at very high speed but has very little torque. The Honeywell T55 gas turboshaft puts out 4115 maximum continous HP. Two of these engines are used to power the Chinook helicoptor. The M1 tank is powered by a turboshaft (gas turbine) engine. During developement both diesel and turboshaft versions were built - the army selected the turbine. Large ships can be powered by large slow turning diesels or a gas turbine turboshaft - it takes big time torque numbers to spin those props.

At the farm progress show this summer New Holland had a cut away of their tubo-compounded engine. The engine had an addtional turbo charger down stream of the main turbo charger. Instead of driving a compressor wheel the down stream tubine was geared to the engine. New Holland claimed it returned 40 HP to the engine. Again the turbine spun at very high RPM but had very low torque.

The formula is correct and 1 ft-lb can certainly pull a plow.
Click to expand...
 
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