Why rate engines by horsepower?

[palmtree]

I am confused. Why do they even give horsepower ratings on mowers? Torque must be more important. If it isn't torque then it is something else. I have been mowing with a Craftsman garden tractor for the past 5 years. I don't like it and I am buying a Grasshopper (that is beside the point). My Craftsman has a 22HP Kohler pro engine with 46 inch deck and it has always run fine--never let me down in 5 years. However, when I need to pick up leaves I use my Father-in-laws John Deere 455 with a 21HP diesel and 60 inch deck. Let me tell you it doesn't just have a little more power than my 22HP Kohler--it has an amazing amount more. And even with a much bigger deck. I guess it is torque that makes the difference. Even still, torque values can't be that different can they? Aren't horsepower numbers derived from torque values? Thanks for shedding light.
Brett

[Lumberjack]

Torque changes as engine speed changes.... People generally understand horsepower more then torque specs....

[BCSteel]

I you look at the spec sheets of Kawi, kohler etc. on numerous engines rated at different hp they have the same torque ratings, and same displacment. How is this possable? And why would you want to spend the extra $$ on a higher hp engine that has the same torque as a lower hp engine? BTW these are all gas carb'd engines.

[betterlawn]

Arguably the HP ratings are darn near useless, but its the way its been done for ~100 years. The engines are used on all sorts of applications (mowers, augers, salt spreaders, edgers, etc.) and the HP gives a good relative indication of the power available.

The Torque/Speed curve is what most people who know what they are talking about are looking for. The HP test is calculated using an SAE spec, I don't remember the details. It doesn't surprise me that a 6.5HP and 5.5HP engine might have the same torque at a given speed. However, the 6.5HP would have higher torque at some speeds at least. Since lawnmowers don't transmissions, all the mower manufacturer can do is optimize the running speed. In the case of a tractor where you have a transmission - there a ton of variables that could affect the performance, making two identical (HP) engines behave completely differently.

In short, its not like they are lying about the HP, its just that the HP (as you pointed out) doesn't really give you the full story.

It would be kind of cool if the lawnmower manfacturers would come up with standard measurement for torque at max tip speed. Barring that, the HP should be a pretty good indicator.

In case you didn't know, HP = Torque (ft-lbs)*Speed(RPM)/5252, so torque decreases as speed increases.

Greg

[YardPro]

horse power is defined as the force required to move 500lbs one foot in one second.
it is a measure of work performed, like watts when dealing with electricity.

torque is a measure of rotational force, it equates to amps in electrical systems

[Dirty Water]

You have to remember the a diesel will make peak torque at a very low RPM, so its HP rating will be decievingly low while the actual power (remember HP is just a measure of torque) will be high.

Comparing a gas engine and a diesel engine is pretty much apples and oranges.

Wonder why mini excavators can have 25 HP and pick up 2 ton loads?

[YardPro]

horsepower has nothing to do with torque

torque is rotational force.. that's it

horsepower is a measure of work performed. one horsepower is the force required to lift 550 lbs one foot in one second..

mini excavators can pick up 2 ton loads becuase of hydrualics, not becuase of horsepower or torque...

torque only becomes useful after run through gearing.
a motor with 500 ftlbs is not much good if it only spins at 100 rpm. imagine the gearing required to spin blades, or hydro pumps ar requires speeds... since horsepower is a measure of ourput per time (has a speed componet) is can be very useful.

the two really need to be measures together to get an accurate picture of engine performance.

[Dirty Water]

horsepower has nothing to do with torque


I disagree:

HP = Torque * RPM) / 5252

Obviously they are directly related.



mini excavators can pick up 2 ton loads becuase of hydrualics, not becuase of horsepower or torque...

I think thats fairly obvious, the point was that the extra torque from the diesal engine is able to power those hydrualic pumps despite having less HP than your lawnmower :D


torque only becomes useful after run through gearing.

Again I disagree. Have you ever driven a nice diesal truck? Its really nice being able to drive 20 mph through town at 500 rpm in 4th gear (Which as we all know, is usually a 1:1 ratio), and still have tons of power.

a motor with 500 ftlbs is not much good if it only spins at 100 rpm.
imagine the gearing required to spin blades, or hydro pumps ar requires speeds...

Apples to Oranges. You don't see low RPM engines in dragsters for a reasion, nor do you see low RPM engines running lawnmowers.

The massive diesals that power freighter ships only turn at a 100 rpm (http://www.boingboing.net/2004/04/01/worlds_most_powerful.html)...I'm pretty sure they put out hundreds of thousands of pounds of torque...Still want to call them not much good?

[xcopterdoc]

rate them in KW.. that would solve everything!

[YardPro]

I disagree:

HP = Torque * RPM) / 5252

Obviously they are directly related.




I think thats fairly obvious, the point was that the extra torque from the diesal engine is able to power those hydrualic pumps despite having less HP than your lawnmower :D



Again I disagree. Have you ever driven a nice diesal truck? Its really nice being able to drive 20 mph through town at 500 rpm in 4th gear (Which as we all know, is usually a 1:1 ratio), and still have tons of power.



Apples to Oranges. You don't see low RPM engines in dragsters for a reasion, nor do you see low RPM engines running lawnmowers.

The massive diesals that power freighter ships only turn at a 100 rpm (http://www.boingboing.net/2004/04/01/worlds_most_powerful.html)...I'm pretty sure they put out hundreds of thousands of pounds of torque...Still want to call them not much good?


pick up a physics book and read it. or even a dictionary.

the torque has absolutely nothing to do with horsepower. torque is the measure of rotational force. It has no optput (power per time) componet.

horsepower is the measure of work performed and has a time componet....

horsepower does have an affect on torque, but not the other way around.

torque is one of the componets used to measure HP, but HP is not used to measure torque.


the ship torque is not a legit comaparison ( also over a million ft lbs of torque). as i stated earlier the low rpm's need massive gearing. those ships
gear the prop shafts. and the props are also highly pitched.

this is why diesels are not used in most dragsters - super heavy, need massive gearboxes to get the output rpm's where they need to be.

i am not arguing about gas/vs diesel.... i am a big diesel fan. the only way to go on work vehicles, etc.....

i am just trying to educate on the hp/vs. torque argument...

[betterlawn]

pick up a physics book and read it. or even a dictionary.

the torque has absolutely nothing to do with horsepower. torque is the measure of rotational force. It has no optput (power per time) componet.

horsepower is the measure of work performed and has a time componet....

horsepower does have an affect on torque, but not the other way around.

torque is one of the componets used to measure HP, but HP is not used to measure torque.


the ship torque is not a legit comaparison ( also over a million ft lbs of torque). as i stated earlier the low rpm's need massive gearing. those ships
gear the prop shafts. and the props are also highly pitched.

this is why diesels are not used in most dragsters - super heavy, need massive gearboxes to get the output rpm's where they need to be.

i am not arguing about gas/vs diesel.... i am a big diesel fan. the only way to go on work vehicles, etc.....

i am just trying to educate on the hp/vs. torque argument...


If you have two mowers that both run at the same shaft/blade speed, than the available torque is directly proportional to the horsepower.

How can horsepower be related to torque but not the other way around? Why is this still being discussed?

HP = Torque * RPM) / 5252
Torque = HP/(RPM*5252)
RPM=HP*5252/Torque

[dfischer58]

1) Thread has degenerated from original question.

2) HP and Torque are clearly inter-related and all the arguments in the world won’t change that.

3) A 5 year old gas motor won’t have the power of a new engine, and will likely fall over power wise faster then a diesel.

4) Gas motors have a significant opportunity to fall out of tune.

5) Nobody says the crapsman deck is as efficient as the Deere. In fact, way in the world are you even surprised?

6) 60 inch deck Deere? Isn’t that a powerflow head attached?

7) If, all other things are equal (and as I’ve mentioned, they’re not) a gasser falling off it’s power curve can drop rather quickly. A diesel won’t. Hence, under a load that will reduce RPM, the diesel will typically deliver more of it’s power during then the gasser at a reduced RPM.

Note I’ve used power, not torque or HP. HP is really just a measure of an engines ability to create more “work” via spinning faster. And I consider that a legit, even valuable measure of power. Torque is something also worth knowing, and in many cases I value it over HP, but I don’t consider one more important then the other.

I would concur that a published HP and torque curve is the ideal.

[Dirty Water]

If you have two mowers that both run at the same shaft/blade speed, than the available torque is directly proportional to the horsepower.

How can horsepower be related to torque but not the other way around? Why is this still being discussed?

HP = Torque * RPM) / 5252
Torque = HP/(RPM*5252)
RPM=HP*5252/Torque

Thank you. I've been moving and havent had the net for a while, or I would have replied this :)

[marvinlee]

Firms, and users, refer to horsepower because it is a shorthand way of finding out one detail of the engines power output--its maximum power. A very careful analysis of a user's needs would compare the engine's power curve, available from almost all engine makers, against the power demand curve of the equipment being powered. This becomes a lengthy investigation, especially for something like tractors where power needs vary greatly from user to user and job to job.

Another facet is that some firms rate their engine's power at one, high, RPM, but govern it at a lower RPM in the equipment. That is the case for my Kubota ZD-21 which might, on a very good day, be capable of putting out 21 horsepower at 3600 RPM on a factory test bench, but which is governor-limited to 3200 RPM as installed in the ZD-21. I estimate it puts out about 18-19 HP as installed.

Sometimes, companies just lie. The Sears 27 HP garden tractor with the Briggs engine uses an engine that even Briggs does not claim 27 HP for.

[Dirty Water]

Sometimes, companies just lie. The Sears 27 HP garden tractor with the Briggs engine uses an engine that even Briggs does not claim 27 HP for.

Hehe...i think this is the same one that advertises itself as a "turbo twin cylinder", yet a quick glance yeilds no turbocharger :)

[UNISCAPER]

The only thing that matters when determining more torque is size. Size, CUBIC INCHES, not girly man liters is the one thing there is not substitute for. Take a 350 cubic inch Chevy, 500HP, with 500 ft lbs of torque at 3200RPM. Then, in the exact same truck, take a 502 cubic inch V-8, with 500HP and 500 ft lbs of torque at 3200RPM. Add a 10,000 lb trailer to each. Drop the starting flag at the foot of a 7°, 4 mile grade.
The trucks will start even, the 350 will begin to pull away because it is less weight than the 502. As soon as you hit the 1/8 mile point, the 502 will pass the 350 and after that all it will see is the tailights of the 502.

In 1969, Bobby Allison was the first to break the 200MPH speed barrier at Daytona in a 426 cubic inch Hemi powered Dodge Charger Daytona. Last year, the 360's NASCAR currently runs could not hit 200 and that is in far more aerodynamics on the cars than the Charger Daytonas had.

Same thing with mowers. Add the fact that there are now 4 ways horsepower ratings are tabulated and you have some pretty skued, distorted ratings. Give me two engines with the same tourque rating at the same RPM, one being larger than the other. The larger displaced engine will always prevail.

[Dirty Water]

The only thing that matters when determining more torque is size. Size, CUBIC INCHES, not girly man liters is the one thing there is not substitute for. Take a 350 cubic inch Chevy, 500HP, with 500 ft lbs of torque at 3200RPM. Then, in the exact same truck, take a 502 cubic inch V-8, with 500HP and 500 ft lbs of torque at 3200RPM. Add a 10,000 lb trailer to each. Drop the starting flag at the foot of a 7°, 4 mile grade.
The trucks will start even, the 350 will begin to pull away because it is less weight than the 502. As soon as you hit the 1/8 mile point, the 502 will pass the 350 and after that all it will see is the tailights of the 502.

Uh, Your totally incorrect here.

Your figurative 350 and a 502 may be produce the exact peak horsepower and torque, but they will produce them in a totally different power curve. You will also never find a 350 and a 502 producing the exact same power at the same RPM.

The power curve combined with the gear ratio of the transmission and rear-end will determine which truck is the stronger puller.

Also, your "girl man liitres" is just a measuremant of engine size, same as cubic inches.

Seems to me like you've got a case of muscle mania, and you need to do some reading.


In 1969, Bobby Allison was the first to break the 200MPH speed barrier at Daytona in a 426 cubic inch Hemi powered Dodge Charger Daytona. Last year, the 360's NASCAR currently runs could not hit 200 and that is in far more aerodynamics on the cars than the Charger Daytonas had.

Oh...I see why you like big cubes....your a nascar fan, makes sense now :)

The larger displaced engine will always prevail.

Nonsense, the only thing a larger displacement engine is gauranteed to be is less fuel effiecient.

[UNISCAPER]

Well Jon you meet all kinds in this forum. Obviously, you have not been around means of true power for any length of time and resort to reading magazines for your wisdom., Nothing wrong with that, but as mu grandfather used to have on the test tank of his marina..."One test is worth a thousand expert opinions"

The two trucks I mentioned, actually did race up that grade. And, the results were what they are.

Liters are what the girly man Europoean and Jap rides are measured by. Real American muscle is measured and always will be measured in cubic inches. Thus, the mix of my CSX4000, an Shelby American car derived from a dying 50's style English sports car, with an aluminum 427 tunnel port side oiling Ford, using Hillborn fuel injection. 0 to 100 back to a dead stop on 12 seconds. Top speed 175. At a local 2 mile road course, there was not one Ferrari, Porsche or BMW that could get near it. 730 foot pounds of torque, 900 plus rear wheel horsepower, and 2000 lbs of car. And yes you are right on one thing only here...It has a 45 gallon fuel cell in the trunk. And, after a 1 hour race, there is not too much left in the tank.

As far as gear ratios, the 502 powered truck had 3:73 gears. The 350, had 4:10's.

In 2008, Mack will be producing an inline 6, 985 cubic inches, thats 16 liters in girly man measurements, which, produces 580 hp, has 1700 foot pounds of torque, and the air comming out of the stack is cleaner than what goes into it. Where over the road trucks now are hard pressed to get 6MPG, this truck has already tested at 8MPG.

Small when you are trying to pull anything, or trying to get somewhere in a hurry, is never better. Smaller will get the job done, just not as fun getting there.

[Dirty Water]

Well Jon you meet all kinds in this forum. Obviously, you have not been around means of true power for any length of time and resort to reading magazines for your wisdom.

A few years ago I made 320 horsepower and 380 ft lbs of torque out of a 2.2 "girlie Man Litre" engine. No magazines here. It would hand most engines twice its size its ass, and still got 28 mpg.


The two trucks I mentioned, actually did race up that grade. And, the results were what they are.

If you got a dyno sheet of both trucks, you'd see that they have a very different power band. That, combined by different gears and different weights etc, makes the difference.

All I'm saying is that if you could (and you won't be able to), get a 350 and a 502 to have the exact same power curve and peak HP/TQ, they would perform the same...Truth is though, in the real world you can't do that.


Liters are what the girly man Europoean and Jap rides are measured by....blah blah blah...I know what I'm talking about because I have a bunch of cars...blah..blah...blah

I fail to see your point.


In 2008, Mack will be producing an inline 6, 985 cubic inches, thats 16 liters in girly man measurements, which, produces 580 hp, has 1700 foot pounds of torque, and the air comming out of the stack is cleaner than what goes into it. Where over the road trucks now are hard pressed to get 6MPG, this truck has already tested at 8MPG.

While we are on the topic of turbodiesels (which has nothing do to with large displacement gas engines), cummins current inline 6 will hand most engines their ass too.


Smaller will get the job done, just not as fun getting there.

Obviously you've never driven a Subaru WRX STI (300hp, 300tq, stock...2.5 litres)...Or my mazda.

[AWJ Services]

Actually engines do not produce HP only torque.
Hp is a flawed reading when taken by a dyno.

The modern day unrestricted Nascar engine is making 100 hp more than it's largest ancestors ever made.

The lower the engine reaches peak torque the more efficient it is.
The higher the the rpm the hp peak occurs the faster the drag car will be.\



A few years ago I made 320 horsepower and 380 ft lbs of torque out of a 2.2 "girlie Man Litre" engine. No magazines here. It would hand most engines twice its size its ass, and still got 28 mpg.

With a power adder I am sure.

[Dirty Water]

Actually engines do not produce HP only torque.
Hp is a flawed reading when taken by a dyno.


That was said earlier in the thread when I said HP and TQ are interrelated, back when YardPro was trying to say they were not.


The lower the engine reaches peak torque the more efficient it is.

Why Diesals are awesome :)

The higher the the rpm the hp peak occurs the faster the drag car will be.

Why diesals suck ;-)


With a power adder I am sure.

It goes something like this:


Theres no replacement for Displacement.
Except for the turbo in my basement.

:D

Custom turbocharged 12 valve SOHC 2.2 litre inline 4. Custom fuel injection setup, 18 lbs of boost.

[xcopterdoc]

There are only seven base units of measurement: distance, time, mass, temperature, electric current, amount of substance and luminous intensity. Each unit can be determined by scientifically reproducible results (no more horses and thumbs!) and all units and standards used today can be derived from those basic seven. An international system, SI, maintains the agreed upon standards for all of these basic units.
Every gearhead wants more horsepower, but what exactly IS horsepower? What does it measure? Horsepower is just like inches or pounds, an arbitrary unit created from a common reference point that everyone can understand. In today's world of advanced scientific instruments, horsepower hangs on, even though it is a little imprecise. Those high minded keepers of the units and standards that quantify everything with precision would rather toss out this well known measure and substitute kilowatts. That Corvette has 298.28 kilowatts, hmm... 400hp just sounds better.
We test generator engines with a resistive load bank. We hook the generator end to the load bank and start loading it up. Its really nothing more than a large heater. We make sure that the engine will carry the given load(measured in kilowatts) and maintain 1800 rpms (for 60 hz) If it bogs down, we look at the engine not the generator end. So.. in a nut shell we are dyno testing the engine using a generator. To test the generator itself, you must use a reactive load bank.

[AWJ Services]

Physics is really not flawed.Hp as a measurement is not flawed.
The way we measure hp is flawed.

Dynos fall in 2 categories.
A brake dyno and an inertia dyno.

Both are flawed.

So if Kubota measures there engine Hp with a brake dyno at a 600 rpm per sec acceleration rate and New Holland uses a brake dyno at 200 rpm per sec acceleration rate.
They are not the same.
What about correction factor?
It plays a big part also.

[xcopterdoc]

Thats exactly the problem with HP ratings. No set standards for testing. There ARE set standards for vehicles but they arent the same standard for lets say maybe a single cyl gas engine or a farm tractor. So whats the point? Test every engine the exact same way and call that number horsepower.

[Redneckn]

I am not going to get into the maximum hp discussion here. right now anyway... I have a 460 in my truck. wanna play? no, kidding.


ok.. why is it when talking farm tractors, they will tout the hp of the tractor? like oh, it's 92 hp. but the pto is only 76 or 80 or some crap like that. i dont care of the engine has a hp rated at 2 just so long as the pto hp is rated at 80.
that crap makes me mad. i mean, with a farm tractor, you arent looking for speed or any of that crap. you are looking for "working load on the pto" type numbers.

[bigz1001]

Efficency. Through gearing, pumps, pto, and everything else efficency is lost.

Also, wana know why stock cars no longer can run at 200 mph? Restrictor plate.

[Redneckn]

stock race cars? you mean like nascar? they still do that? i thought that finally went away and all those guys got a life and brought it out to the drag strip.

*kidding* sort of

[UNISCAPER]

Also, wana know why stock cars no longer can run at 200 mph? Restrictor plate.

True, except, when cars ran 200 MPH using 426 single quad Hemis and 427 Hi deck Fords, (otherwise called the tunnelport-side oiler) and lets not forget Junior Johnson's '66 427 cubic inch Chevelle which topped 197, they hit 200 MPH without using the aerodynamics and wind tunnel times the one size fits all bodies NASCAR runs today. Size when pulling a heavy load, or going fast is the one thing that will compensate for all inefficiencies. Now, give me a 426 B block hemi in one of the new body styles, scale out all four corners, there would not be one single car that could keep near one running a small block.

I'm with the late great Dale Earnhart on this one, they should let the teams do whatever they want to make speed and force the track owners to build safer raceways.

[YardPro]

[QUOTE=JonHolland]That was said earlier in the thread when I said HP and TQ are interrelated, back when YardPro was trying to say they were not.

i don't think i said they were not interrelated.....

i'll restate what i think i said.

torque is ONLY a measurement of rotational force.....period... there is no rpm, componet.

horsepower is a measurement of work produced in a time period......

torque alone cannot be accurately used to measure engine output.
here's an example:
you have an engine that puts out 700 ft lbs of torque.............. how do you use this number????? you cannot use it unless you have an rpm figure to go with it.

you have that 700ftlb motor, but it only turns 200 rpm, how do you use that power????? you have to really gear it up........


now you take the same motor and give a HP number or a KW number and it can be plugged in to formulas and you can use them to figure performance.

[AWJ Services]

Actually engine dynos only use torque without rpm .They use rpm to determine HP.Hp is a deriative of torque as far as engine dynos are concerned.
700 ft llbs of torque is the same no matter what the rpm.
On a dyno you actually hang a weight too calibrate the torque gauge.


True, except, when cars ran 200 MPH using 426 single quad Hemis and 427 Hi deck Fords, (otherwise called the tunnelport-side oiler) and lets not forget Junior Johnson's '66 427 cubic inch Chevelle which topped 197, they hit 200 MPH without using the aerodynamics and wind tunnel times the one size fits all bodies NASCAR runs today. Size when pulling a heavy load, or going fast is the one thing that will compensate for all inefficiencies. Now, give me a 426 B block hemi in one of the new body styles, scale out all four corners, there would not be one single car that could keep near one running a small block.


Bill Elliot actually did some testing with his car in 86 87 time period at Taledaga with an un restricted smallblock and reached speeds of over 237 mph.Cup engines of that time period were down 100 hp to what they are now.

[YardPro]

[QUOTE=AWJ Services]Actually engine dynos only use torque without rpm .They use rpm to determine HP.Hp is a deriative of torque as far as engine dynos are concerned.
700 ft llbs of torque is the same no matter what the rpm.
On a dyno you actually hang a weight too calibrate the torque gauge.

you are absolutely correct.
torque is more or less a static value.
to convert torque to work (HP) you need movement (RPM).
since you neet to spin a tranny, driveshaft, and tires, you need to use rpm's


here's the question.....

you have a 3500lb car with a motor that has 700ftlbs torque... how fast can you expect the car to go??????

anyone care to calculate this out with ONLY the torque value

you can't do it.

[Redneckn]

uhhhhhh. not more than 192.465 and not less than 15 (give or take 1)

[YardPro]

LOL

there are formulas you can plug in vehicle wieght and HP and get a rough idea how fast it will go...

there are none tor torque becuase torque is a static measurement....
there is not delivery rate for the force
hp is used becuase it has a delivery rate.

Hp is defined as:
Horsepower is defined as work done over time. The exact definition of one horsepower is 33,000 lb.ft./minute

so hp is describes the delivery rate of torque........

the opposite is not true for torque, there is no delivery rate for torque....
having ONLY a torque rating for a motor leaves out the most important componet of power output.... how fast it puts out the power.

check out this link

http://www.web-cars.com/math/horsepower.html

[UNISCAPER]

"having ONLY a torque rating for a motor leaves out the most important componet of power output.... how fast it puts out the power."


And in the same weight vehicle, with the same aero dynamics, a larger engine will get that car to a higher speed, faster. Thus, bigger is always better if you have alot of weight to pull, or have to get to a high rate of speed in a hurry. Case closed.

[gro2mow]

Ok, I have been demoing a Country Clipper Charger 52" which has a Kohler 23HP which develops a torqe rating of 40.2 ft/lbs @ 2400 rpm's. Since a 25HP Kawasaki developes only 41.3 ft/lbs @ 2400 rpm's, I would assume there would not be any great benefit to move up in HP even if I go with a 60" deck.

The Chargers don't weigh nearly as much as most of the other commercial mowers. I think JD uses 23HP Kawasaki motors on mowers weighing in at 1200-1300 lbs. The Charger only weighs 860 lbs with a 60" deck. So am I safe to assume the 23HP Kohler would be enough engine?

It has plenty of power for mowing a 2.5' deep field with a 52" deck and not really ever bogging down.

[thecrankshaft]

0 to 100 back to a dead stop on 12 seconds

How big was the tree that you hit? Was it a redwood?

[AWJ Services]

Ok, I have been demoing a Country Clipper Charger 52" which has a Kohler 23HP which develops a torqe rating of 40.2 ft/lbs @ 2400 rpm's. Since a 25HP Kawasaki developes only 41.3 ft/lbs @ 2400 rpm's, I would assume there would not be any great benefit to move up in HP even if I go with a 60" deck.


The engine does not operate at 2400 rpm so the engine with the most torque at it,s operating range will be the best.
Most are set in the neighborhood of 3600 rpm.So with the almost I dentical torque output of these 2 engines the one with the most torque or hp at 3600 rpm will be the better engine if they are both measured the same.

[fastlane]

Maximum HP and maximum torque do not accure at the same rpm. Torque fades before max HP is reached.This is why race cars shift in the power band. not at max rpm. There is no substiute for size. When the Ford GT40s won the world championships back in the 60s the 427ci was about twice the size of the European motors They put out about the same HP/torque at half the rpm and dominated.The max. motor size was changed to 3.L and the fancy red cars were back on top.

[AWJ Services]

I guess I am more informed than most .I actually run an engine dyno and have full access too a performance engine building shop.
My previous carreer was in the automotive industry.
Since hp is a derivative of torque it is directly related too torque.We can exclusivley use torque as measured by the modern engine dyno as measuring stick for performance.Since engine dynos only measure torque and calculate hp from it.Tourqe does go lower as rpm increase but since more power pulse are applied in a certain time period then the lesser torque can do the same amount of work as the higher torque at a lesser rpm.Hence they cross at 5200 rpm since that is in the formula too calculate hp from torque on an engine dyno.In the performanc eindustry we attack the average hp or torque over the operating range.If a mower typically runs between 2400 rpm and 3600 rpm the one with the most average power will perform the best.It is often described as a flat torque curve.

[UNISCAPER]

"Maximum HP and maximum torque do not accure at the same rpm. Torque fades before max HP is reached.This is why race cars shift in the power band. not at max rpm. There is no substiute for size. When the Ford GT40s won the world championships back in the 60s the 427ci was about twice the size of the European motors They put out about the same HP/torque at half the rpm and dominated.The max. motor size was changed to 3.L and the fancy red cars were back on top."

Now that is what I'm talking about. I did not hit any trees to do a start/stop in 12 seconds. It's called a CSX4000 Shelby-American Cobra with an all aluminum Holman-Moody 427 tunnel port side oiler aspirated with Hillborn port injection. 900 rear wheel horsepower, 2300 lb car.

I had the priveledge of riding in a GT-40 several years ago at the Laguna Beach road course. Enzo would have been rolling in his grave when he saw it pass the F-40's and 50's on the same track. That was F-40 and 50's measured in girly man size not cubic inches.....

The GT-40 was so far ahead of it's time, when it was reintroduced, it still turns heads...The biggest dissapointment is in the girly man sized blown engine Ford chose to power the GT, because, there is NO subsitute for CUBIC INCHES....... Now if an enterprizing person who can afford the GT would posess the wisdom to purchase a Holman Moody tunnel port and install it in the car, imagine the possibilities....:):):)

[Dirty Water]

"Maximum HP and maximum torque do not accure at the same rpm. Torque fades before max HP is reached.This is why race cars shift in the power band. not at max rpm. There is no substiute for size. When the Ford GT40s won the world championships back in the 60s the 427ci was about twice the size of the European motors They put out about the same HP/torque at half the rpm and dominated.The max. motor size was changed to 3.L and the fancy red cars were back on top."

Now that is what I'm talking about. I did not hit any trees to do a start/stop in 12 seconds. It's called a CSX4000 Shelby-American Cobra with an all aluminum Holman-Moody 427 tunnel port side oiler aspirated with Hillborn port injection. 900 rear wheel horsepower, 2300 lb car.

I had the priveledge of riding in a GT-40 several years ago at the Laguna Beach road course. Enzo would have been rolling in his grave when he saw it pass the F-40's and 50's on the same track. That was F-40 and 50's measured in girly man size not cubic inches.....

The GT-40 was so far ahead of it's time, when it was reintroduced, it still turns heads...The biggest dissapointment is in the girly man sized blown engine Ford chose to power the GT, because, there is NO subsitute for CUBIC INCHES....... Now if an enterprizing person who can afford the GT would posess the wisdom to purchase a Holman Moody tunnel port and install it in the car, imagine the possibilities....:):):)

You can talk about your fuel guzzling domestic engines all you want, but you cannot argue that you guys are wrong and that AWJ is right.

[AWJ Services]

I have a good friend who specializes in 427 , 428 style engines and he has a friend that actually owns a real GT40 circa 1960's era.It is awesome.

I have actually touched it and heard it run.
What a beast. :blob3: :blob3: :blob3:

My buddy builds over 100 of these engines and ships them all over the world.All through the years he bought them up for scrap value from junkyards and swap meets and now he has a wharehouse full of theses engines.A 427 bare sideoiler block goes for over 4500 bucks right now.

[UNISCAPER]

AWJ:

It is almost getting to the point where the Holman-Moody aluminum blocks are cheaper. The guts still cost the same, and just because it says Ford and not Chevy you will pay through the nose. I remember when you could buy GT-40's all day long for $10K, back in the 60's after Ford abandoned it's racing program, no one wanted them, just like a Cobra. Holman Moody bought 9 of them and several GT 40 Mk 4's and had to sell them to save their shop back in the late 70's early 80's or so....
One of the guys in the Cobra club I belong to paid $12,000.00 for his last production model 427SC, circa 1967. He has turned down offers for well over 500K and still drives it every day. Then there is Mr. Gallant, who owns a truck junk yard in Oceanside, Ca. He has 2 GT-40,s, 3 Cobras and several Shelby Mustangs that have never seen the street, always always made as race cars....

Those side oiler blocks are rare finds indeed. The coast here is a haven for high performance Ford products of all vintages.

.

[YardPro]

"having ONLY a torque rating for a motor leaves out the most important componet of power output.... how fast it puts out the power."


And in the same weight vehicle, with the same aero dynamics, a larger engine will get that car to a higher speed, faster. Thus, bigger is always better if you have alot of weight to pull, or have to get to a high rate of speed in a hurry. Case closed.

i agree with you 100%

remember the origional question posed by this thread though....
"why even use horsepower as a rating"?

[UNISCAPER]

It is the alure.....While HP has some bearing on a vehicle purchase, the two real performance determining makers are torque, and size. Such as the case with the guy and his 300HP Subaru I blew off the road from a light going up a 7° grade over a 3 mile run. his engine makes alot of HP for a 200 cubic inch motor. It has not got the torque or the size to pull a booger out of a wet bucket of snot. And, even though my 3500 series diesel truck weighs 7000 lbs, it's engine is twice the size, and produces 3 times the torque. On flat ground, he would have stomped me but he was litterally fighting an uphill battle.

ll While searching my old Ford data, I happened upon the old racing specs of the 427 cubic inch Ford SOHC engine. (that's 7 liters for those of you who measure in French girly man increments) Single overhead cam Hemi combustion. 625 factory HP, with a whopping 510 footpounds of torque, at get this...7500 RPM on a big block!

So, back to lawn mowers, lets bring this one to light...You have a 61" Scag three wheeler with a 23HP Kohler. It is 52 cubic inches for arguement sake with a torque rating of 60 ft lbs at 3600RPM. You then take the same machine, install a 21 HP Lombardi 2 cylinder, 79 cubic inch diesel producing 80ft lbs of torque at 3600 RPM..

Where after a rain, that Kohler is going to be gaging while trying to run full speed, the Lombardi will glide through at full speed and will have gotten there in half the time.....

[Redneckn]

So that would all explain why the 460cid in my old Ford is only rated at about 260hp but can pull full grown red oaks up? ok. maybe not FULL grown red oaks. but you do get my drift.. because i can sit at a red lite, come off the brake, hammer the long skinny pedal and it will get on down the road and will spin the tires for no less than 1/8mile or until i let off of it.
you can pat the gas and it make the truck frame do this odd little "twist" like motion...

so the HP rating is pointless because the torque is so high...


btw, i am looking to make more of this torque stuff if anybody would care to donate ideas or money.. thanks.

[Tigerotor77W]

Part of the question is how each is defined. Torque is the measure of how a force acts through a radial distance, as YardPro has mentioned time and time again. No one cares how that matters because there is nothing associated with TIME when simply talking about torque. Think about it: when you need to tighten a nut, you get out a torque wrench to tighten the nut to the specified figure. Who cares if you whip the wrench as fast as you can and tighten it in five seconds, or if you rotate one complete revolution in a minute? You simply tighten until the dial or readout is correct. Torque is a force applied through a distance. Directly, there is no correlation between torque and horsepower.

However, on an engine, as AWJ was mentioning, things change. The fuel and combustion characteristics of an engine determine its horsepower and its torque curves -- which may be related. As I haven't gone through courses dealing specifically with dynos, I can't be sure on this one.

About the original question: it could be that horsepower, in its very definition, measures the ability of something to do some amount of work in some period of TIME. Therefore, when you want to describe to someone that, say, a car is better than another because it's faster, using "power" to differentiate the two makes sense. If the two cars are similar in weight, then the one with more power, in the public view, should be faster. Unfortunately, transmissions, gearboxes, and governors all change the way power is relayed, which makes it only a misconception now. Given that only about 60 hp is required to take a car up to 120 mph and keep it there, who would want a 60 hp car? Other than Europeans, who drive SMART cars.

In my opinion, horsepower is not the only factor in determining capability. It is, however, the most widely recognized one. And at times, this being one of them, perception is what matters most. More than fact, and certainly more than reason.

[UNISCAPER]

Bobcat:

You hit on another area of concern, the ever increasing need for manufacturers to add more gears to a vehicle. Loose some of the engine, rate by the girly man system of measurement, and add gears because the downsized motor can't pull a booger out of a wet bucket of snot. Thus when the first DT466 cornpickers came out. They were 220HP and 560 cubic inches. You then take a Mack 237hp engine at 740 cubic inches and that Mack will eat a cornpicker alive all day long on the same amount of fuel.

If you have to have more than 4 gears in a truck transmission you need a larger displacement engine.
In many driving situations in our mountains and valleys, adding gears does not help you get to the top, the real culprit is you have run out of engine half way up the grade. Given similar torque and HP curves in the same vehicle with the same load, both torque and horsepower can be easily compensated by adding engine size. My personal selection would be a 707 cubic inch Arias in a Chevy C-30 and a 4 speed automatic.

The ancient comparison will be like hitching a 4000 lb wagon to a 1/4 horse, and hitching that same wagon on a Budweiser Clydesdale draft horse and pulling it to the top of the same 6 mile hill. Assuming that 1/4 horse even makes it to the top, the draft horse just glides right throught it as though it was normal routine. Until you can effectively compensate size, torque and hp are only going to be secondary considerations for heavy loads and hills, or wet grass and mowers.

[AWJ Services]

Torque does not need a time measurement.
Torque is always the same but when engines are concerned HP is not.
Saying that is why the guy came up with the formula to derive hp from torque.
The engines rpm is the rate of torque or the time measurment.

Take 400 pounds of torque at 3000 rpm
and 400 pounds at 4000 rpm.They are both the same torque output ,but the 4000 rpm torque rate is less than the 3000 rpm torque rate Resulting in a higher hp reading.

So torque really does have a time measurment when engines are concerned.

[Tigerotor77W]

As far as engines are concerned, that's what I was saying -- the two are related. Because the two engines are putting forth the same amount of work -- in AWJ's example, 400 foot-pounds -- and one is doing it faster (4000 RPM vs 3000 RPM), there is more power being transferred by the 4000 RPM engine. Which throws in another issue because very few engines have the same torque at RPM differences of 1000 RPM.

At any rate, glad that's settled... now I've got a better understanding. Thanks.

[AWJ Services]

What I am saying is not Physics and text book correct.There is a reason why and that is the orginal idea and the mathmatics involved in engine dynos is severlly flawed from the start.
It is a good bench mark ,but there are some issues.
Superflow,DTS,Powertest are 3 big dyno manufactures.
You can take the same engine and place it on all 3 dynos and not get the same reading.
Granted there are several different correction standards ,but even with the same standard they will not read the same.



You hit on another area of concern, the ever increasing need for manufacturers to add more gears to a vehicle. Loose some of the engine, rate by the girly man system of measurement, and add gears because the downsized motor can't pull a booger out of a wet bucket of snot. Thus when the first DT466 cornpickers came out. They were 220HP and 560 cubic inches. You then take a Mack 237hp engine at 740 cubic inches and that Mack will eat a cornpicker alive all day long on the same amount of fuel.


Engines have a thing called inertia that affects the dynos reading during engine acceleration.
The higher the rpm the more effect inertia has.
Take a diesel with huge internal weights that operates between 800 rpm and 1800 rpm.
Take a smaller diesel with less inertia that runs from 800 to 3500 to obtain similar dyno readings.
This is why large diesels rev so slow and are so hard too lug down and how small 3 cylinder diesels that run at 3500 rpm do not seem too have as much grunt down low but when bogged down recover very fast.

Take my Kubota Tractor.
L 3710.It has a 4 cyl diesel.
The one under it with 4 less hp is 3 cylinder that operates at 1000 more rpm.
My tractor will work circles around it.Take the next size up Kubota with 6 more hp and it is hard too tell the difference between it and mine.


Enough ranting ,but I really love this stuff.

Thanks Bobcat S250 you brought up some excellent points .

[Tigerotor77W]

Same to you -- engines continue to amaze me. If their timing alone in creating power isn't enough, throw in electronics to manage fuel burn and combustion... and I'm lost forever. :D