I'll admit. I was wrong too. (torque versus HP)

[rancherman]

Just got home from my 250 mile round trip out into the hill country of Ne, and brought home some cows.

Believe me, This has been bugging the hell out of me.

First of all, I decided to call on the big gun.

My Dad was an mechanical engineer, and I had quite an upbringing as a kid. a lot of principles were hammered home.. Almost Nazi style.

Now, 45 years later, some of these principles are a little hard to bring out of the archives! My career path took me out of the loop for studying and practicing the sciences.

Dad passed about 10 years ago, I sure miss being able to call him up and quiz him about how to build this, or what materials to use here..

So, I did the next best thing! I called my Uncle John. He is a tenured physics professor and rabid car builder. perfect.

I had him view my miserable attempts at explaining how the HP= T*RPM/5252 applies here.

He said: We all had some valid points, but more interestingly was some points were correct, but for the totally wrong reasons.

First off:

My analogy of the 2 electric motors with identical torque, but double the speed. motor #1 would indeed have 1 horsepower, and would lift the 550 lb weight in 1 second. Motor #2 would then indeed have 2 hp. only because it's turning 2x the speed. It would indeed lift the weight at 2x the speed as the 1 horse motor. I was wrong there.

He said I need to forget the initial acceleration of this weight.. and concentrate ONLY on the performance of the weight going up the rope.

he said both motors will struggle momentarily as they spin up to speed.. Motor 2 will struggle just a tad longer ONLY BECAUSE IT HAS HIGHER TO GO.. AND spin up time will be longer.

This is no consequence. It's the performance of the speed of the weight After the initial acceleration.

What this boils down to, is torque is what moves the weight at the certain speed. John pointed out that it doesn't take any more energy to move the weight upward regardless of speed (well until air resistance becomes a factor!)

since both motors are equal torque, they are able to lift the exact same amount of weight. Motor #2 will do it 2x faster, not because of the HP, but because it's wired to run that rpm in the first place.

John said we need to look at HP as an 'after effect'. It's the PROOF of work being done, or the potential of work to be done.

again, this is after both motors have accelerated the weight to it' full potential.. then the test begins.

Now, look at it this way: after the test, we can now measure the performance of both motors. #1 did a 1 foot per second, #2 did it in half the time. both with identical torque. Because of this fact, the #2 motor did in fact move the weight in half the time, it should be considered 2 hp.

HP again should be looked at as the 'after effect'.

Why? John told me to visualize both motors doing their finest with the weights attached.. and pulling the weight up a 100 foot cliff. (for better visualization here). Halfway up both runs, I take an additional 55 lbs and put on each as they buzz by. Both motors will suffer proportionally, actually this would be 10%. means Motor #1 is now hoisting the weight 10.8 inches per second, and motor #2 would be hoisting the weight 21.3 inches per second.

Now, lets apply this to 2 identical cummins powered vechicles. both are bone stock. but one will have a governor that stops ALL rpm progression beyond 3400.. and the other having this stop @ 1700. Both will have identical fueling properties.

Engine 'a' will be exactly double the HP of Engine 'b'. This is because of the doubling of the rpm. Both here have exactly the same torque. (same fueling, same air)

Both are also geared identically too.

What's the difference? MAX SPEED. Both will accelerate side by side.. and when the governor kicks in on the slow motor.. that truck will march along @ what, 55 miles per hour... while the other truck continues up to 110. Why? not because of the HP. it's because the governor allowed it to.

This is where we need to look at HP as the AFTER EFFECT. Yep, that motor propelling the truck down the road at 110 mph was indeed making double the horsepower... only because it was allowed to spool up to double the rpm.. But no more fuel for the acceleration, than the first motor was added. The acceleration and maintenance level of fueling is next on the list;

John told me about the 'butt feel' of why our trucks seem to 'hold better' at 2500 rather than 16-1700 starting point..

Look at where we are at on the torque curve. Even though 1700 and 2500 are pretty even for torque, the guy that is @ 1700 is right on the brink of falling off the cliff.. The guy already @ 2600 has 900 rpm of 'play' before the truck falls off. John said momentum helps.. for a split second! not what I'd call a real helper!

So, lets now apply this to the 2 cummins powered trucks from the last paragraph.

Lets send them both down the road @ 55 mph. (remember, the one truck is governed for 1700, and this is all it has) Both are turning the same rpm.. both are burning identical fuel. Both are producing identical torque... they have to be, otherwise one would be traveling faster than the other..

Since both are fueled identically, the outputs will be identical right up to the point the slower governor stops all upward rpm change. this is where the faster engine begins to pull away from the slower one horsepower wise.. and we are now looking at the electric motor example from waaay above!

Both motors are identical in torque, but because of the rpm difference, the faster one is double the horsepower.

What really needs to be said here is.. no diesel 'makes' torque, (above what is required to maintain a rpm at a no load situation) unless it's needed.

If I keep my foot on the throttle, and have a no load situation on the engine, only a very little amount of fuel is required to maintain the set rpm. It takes very little fuel to keep a non loaded engine at a set rpm. If we could measure the amount of this torque, it'd be minimal to say the least.

So, back to our 2 identical trucks. traveling side by side. Both are CAPABLE of maxing out the torque at say 450 ft. lbs. In order to maintain 55 mph, let say they need enough fuel to produce 120 ft. lbs at the crank to maintain this speed. Or about 40 horsepower.

Lets now introduce them to a hill. still side by side. who thinks the double hp truck will walk away from the other one?

It's a tie. sorry. both will lug to death at the exact same rate. Both are putting down the exact same torque to the rear tires, both are injecting the same max fuel. Why doesn't the double hp engine pull away? because it's not turning the rpms to PRODUCE the double HP. Since it didn't make the rpms, it never reached it's potential.. this is where we need to look at HP as an after effect. You must have torque, AND rpm to produce HP.

John basically told me this as the exact same way he has answered a lot of gear heads in his classes. He also kicked my *** for a couple of knuckle headed answers I gave as well.

"bench racers" will conjecture.. and myths are rampant.. but physics are physics.

I offer my humble apology for any bad thoughts I might've had over the past days posts.

Robert, rancherman

[rancherman]

let me edit.. I type faster than my brain!

I misspoke about the engine #2, It will in fact pull away from the slower governed #1.. as long as the hill they are on isn't overpowering the torque output. It surely will keep on going right up to it's top governed speed if allowed, and the operator wants it to.

...THE EXACT SECOND this motor reaches 3400 rpm, AND WAS STILL PULLING FULL FUEL. we can cheerfully say that motor MADE double the horsepower... after the truck levels off at 110 miles per hour, fuel should diminish, and so will the torque output. horsepower AT THAT TIME is diminished. (although, at 110 mph, full fuel might be required to sustain the speed? LOL) our trucks are pretty big bricks! This why HP is such a fleeting value. Now I understand why rolling dynameters need calibration.. they need to make sure the test subject is fully loaded. If not, how could they even begin to realize potential HP!

This is using a magic injection pump... one that will go to full fuel within say 10 rpm drop from desired rpm. (wouldn't that be a hoot to drive??)

Oh, remembering my old days of drag racing.. Torque gets the car off the line, and HP gets it across the finish line first.

Very true. High torque at high rpm will in fact get us across the finish line first. HP is much sexier and quicker to say!

[CSM]

I can't speak for all, but in my mind, no apologies are necessary among friends.  This is what makes this site great.  We are having a good discussion.  

 

None of this is preaching.  Just discussion, as I am a bit of a nerd, and like this stuff.   Consider the following... You can feel torque and measure it with a torque wrench, as torque is static.  Torque is in Lb*ft and doesn't imply any rotational speed.  Horsepower is torque appled AT an RPM.  Horsepower units are roughly Lb*ft/sec. 

 

So with the above, look at this old very slow RPM engine like the one below in the video.  Its a 100 hp engine.  

 

http://youtu.be/OwOxoSmoWy8

 

If we assume (safe as most of these engines ran at or under 600 rpm) 300 and 500 RPM for this engine at 100 HP I ran the numbers for the torque.  

 

hp=torque*RPM/5252 and torque=hp*5252/rpm

 

At 300 RPM and 100 HP output the engine would be putting 1750 lbft of torque on the output shaft, and at 500 RPM it would be putting 1050lbft of torque on the output shaft.  

 

My truck doesn't make 1750lbft of torque, but I make more power than this old engine and if hooked up to a generator, my truck would make roughly 4 times more electricity with its 400 odd hp than the old engine.  

 

So, as noted, RPM is key, horsepower is torque at an RPM.  The same torque at a higher RPM equals more power and a faster car, if it is geared appropriately. 

 

So, lets consider gearing!  Torque is multiplied up or down by gear ratios and horsepower stays constant (minus parasitic friction loss) through gearing. Yet, even though torque is multiplied, it is still a static measurement and dosn't imply any rotational speed.

 

I can gear a 5hp briggs and stratton down to the point to where it will pull a freight train, but very very slowly.  That briggs and stratton could conceivably put out the thousands of ft*lbs of torque needed to turn the wheels.  However, it doesn't have the power to do it at a high RPM and haul the mail.  

 

Our engines torque & power curves are deceiving, as they have high torque numbers compared to cars of equal horsepower ratings.  However, we must consider that our engines turn at 2000 rpm compared to a toyota that may make the same power but at 5500 rpm.  If you could run a toyota engine at 5500 all day long and geared it down, it could tow the same load as our cummins, but we all know it would burn itself out at that high RPM.  

 

They are linked, but the rate that the torque is applied has to be considered. 

Edited February 28, 2015 by CSM

[Nekkedbob]

A simplistic way that it was explained to me 40 some years ago is torque gets you started from a stop, horsepower gets you up to speed and torque holds you there.

[Wild and Free]

A simplistic way that it was explained to me 40 some years ago is torque gets you started from a stop, horsepower gets you up to speed and torque holds you there.

Similar old saying is Hp is how fast you can hit the wall, Torque is how far you can push the wall.

[rancherman]

csm.. not sure where you are headed with the torque is static. static to me means 'stationary', 'unchanging'.

Torque output is certainly 'changing' in our engines. all dependent on how much fuel and air is above each piston when it fires. There certainly is a top limit. Is this what you are referring to?

Lots of fuel and air and low resistance behind the crank means the engine accelerates.

when the rolling resistance equals the torque output, the speed stabilizes.

when the rolling resistance exceeds the torque output, the speed goes down.

rolling resistance here means everything trying to hold the truck back. friction, gravity if on a hill, the acceleration of a mass, air resistance.. everything.

When we accelerate this engine and want it to accelerate it up to 60.. we increase the torque output by adding more fuel and air to the top of the piston.. causing it to push down harder on the crank... which is the exact mirror of what a dynameter is 'sensing'. it's reading this 'down pressure' at the end of the crank.. Well, the increased torque has to go somewhere! it goes to the ground.. and accelerates the truck.

When the truck reaches 60 mph, we ease up on the fuel and air, which equalizes the amount of torque going out the engine, and what this truck needs to maintain 60 mph.

If the engine can produce 450 lbs of torque at max fuel.. and the vehicle needs 100 lbs. (from the crank) just to pull it through the air at 60 mph..

the difference is how hard it'll accelerate at max fuel. ( I didn't allow for accelerating the mass of the truck here)

We increase or decrease the amount of torque coming out the rear of the engine.. to meet or change the trucks requirement.

we want to accelerate.. we increase torque.

we want to maintain speed starting up a hill, we then increase the torque by adding fuel.

we want to slow down, we remove the torque (fuel)

when we want to just hold the truck at a certain speed, we back off the throttle and when the speed is met, we have equalized the engines torque output and what the truck needs to travel at this speed.

look at what is happening when we take a vehicle out to see what it has for top speed (the truck with our 450 lb torque) going down a flat road, we mash the throttle to wot. Max fuel.

Lets assume there is no computer to limit top mph. no limits on Injection pump rpm either. No defueling anywhere.

.. a mile or so later we feel or see the truck no longer accelerating. It is maxxed out. We can say the trucks needs are equal to the engine output.

because of torque, the engine was able to accelerate. As the resulting rpm climbs, our well known formula shows the net result, or quantity of work being done (in HP) The excess torque caused the engine to accelerate, and when the trucks drag equaled the torque output, it stabilized in speed.

HP= T*RPM/ 5252 With a max torque output of 450, (our example engine) HP goes up for only one reason! RPM CHANGE.

without torque, you can't overcome resistance, and rpms can't climb. HP numbers suffer (do not change)

The 1hp = 550 per foot per second is just another way of that formula.. it was derived from it!

why do we downshift to help accelerate? to increase the torque to the wheels. Why do we have to downshift to help our engine overcome a hill? to increase torque to the wheels. Transmissions are torque multipliers.

I can see where a lot of guys will now say "well, when you downshift, the engine rpm goes up, raising the hp".

Which it does! We made life easier on the engine by downshifting, which allowed it to accelerate to the higher rpm in the first place. Torque requirements have eased. Our formula proves this.

When our increased torque come out the back of the transmission.. the resulting overall driveline torque output to the ground is much higher, causing the truck to either accelerate, or maintain speed on a hill.

[AH64ID]

A simplistic way that it was explained to me 40 some years ago is torque gets you started from a stop, horsepower gets you up to speed and torque holds you there.

 

 

Similar old saying is Hp is how fast you can hit the wall, Torque is how far you can push the wall.

 

 

I have always been told that torque gets you moving, horsepower maintains once your there.

 

If torque held you then horsepower would have no bearing on pulling a grade, and we know it does in application.

 

 

Now, lets apply this to 2 identical cummins powered vechicles. both are bone stock. but one will have a governor that stops ALL rpm progression beyond 3400.. and the other having this stop @ 1700. Both will have identical fueling properties.

Engine 'a' will be exactly double the HP of Engine 'b'. This is because of the doubling of the rpm. Both here have exactly the same torque. (same fueling, same air)

Both are also geared identically too.

What's the difference? MAX SPEED. Both will accelerate side by side.. and when the governor kicks in on the slow motor.. that truck will march along @ what, 55 miles per hour... while the other truck continues up to 110. Why? not because of the HP. it's because the governor allowed it to.

This is where we need to look at HP as the AFTER EFFECT. Yep, that motor propelling the truck down the road at 110 mph was indeed making double the horsepower... only because it was allowed to spool up to double the rpm.. But no more fuel for the acceleration, than the first motor was added. The acceleration and maintenance level of fueling is next on the list;

 

Don't look at acceleration, it's not a good argument with your goverenor example. Instead take the 1700rpm one and put so much weight on it that it can only hold speed at 1650 rpms at WOT. That way we know that 100% of the power is holding it at the speed. Now take the 3400 rpm governor and put it at 1650 rpms, it will be un-accelearated as well. Now approach the same grade at 3000 rpms, go WOT and watch it accelerate. It doesn't have more torque, but it does have more horesepower. That additional horsepower is enough to not only hold the vehicle with a higher power requirement (since the speed is higher) but it has enough spare power that it can accelerate. Horsepower is doing that.

 

 

...THE EXACT SECOND this motor reaches 3400 rpm, AND WAS STILL PULLING FULL FUEL. we can cheerfully say that motor MADE double the horsepower... after the truck levels off at 110 miles per hour, fuel should diminish, and so will the torque output. horsepower AT THAT TIME is diminished. (although, at 110 mph, full fuel might be required to sustain the speed? LOL) our trucks are pretty big bricks! This why HP is such a fleeting value.

 

 

Why is HP such a fleeting value? At 3400 rpms torque is falling off about 1.5x faster than hp :-)

 

 

This is using a magic injection pump... one that will go to full fuel within say 10 rpm drop from desired rpm. (wouldn't that be a hoot to drive??)

 

 

Welcome to the world of Common Rails.

 

 

Oh, remembering my old days of drag racing.. Torque gets the car off the line, and HP gets it across the finish line first.

Very true. High torque at high rpm will in fact get us across the finish line first. HP is much sexier and quicker to say!

 

 

 

High rpms negates the need for high torque, if properly geared. Remember my 1427hp and 700 ft/lb of torque helicopter example.

 

If a 600hp 10,000 rpm engine is geared to make peak power in it's 1/4 mile race then it will do better with its 315 ft/lbs of torque than a 315 hp 5,252rpm engine with 315 ft/lbs. If geared to run the same speed the 600hp will get there first, but makes the same torque.

 

 

The 1hp = 550 per foot per second is just another way of that formula.. it was derived from it!

 

 

That is not a formula, it's a measurement. You are not calculating how long it takes the horse to move the 550lbs, you are measuring it.

 

 

You are still looking too much at acceleration. Think about a static rpm and torque output. I keep going back to the 1600 vs 2500 rpm real world scenario. Both have 800 ft/lbs being made at the crank, which is 3280 ft/lbs with 4.10's to the ground before the standard Dodge 15% drivetrain loss. So 2788 ft/lbs of twist is where the rubber meets the road. One one them has 243hp to do the work with, and the other has 380. The 380 hp scenario will out pull the 243 hp scenario. The way to test it would be to take the engine and load it up so that at 2500 rpms it barely holds on the selected grade, i.e. another 1000lbs and it would slow down. Then slow down (same gear) to 1600 rpms and watch the truck struggle and slow down. This will happen, the horsepower is needed.

 

 

I offer my humble apology for any bad thoughts I might've had over the past days posts.

Robert, rancherman

 

No apologies needed, this is fun :-)

[dorkweed]

My head is spinning now after reading this..................................................no torque or HP required!!!

[AH64ID]

My head is spinning now after reading this..................................................no torque or HP required!!!

 

How fast is it spinning? How much does your head weigh? :duh:

[CSM]

What I mean by the static, is that torque is a stationary measurement.  

 

Torque as calculated at your engine or with a torque wrench is the same.  It is simply a non moving "twisting" force.  With a lever long enough I could make a 1000 ft*lb with my body.  However, I could not move that lever fast enough to make 1000 ft*lb at any meaningful RPM to make any significant horsepower.  

 

I don't mean this to be cryptic or secretive.  Thats all torque is when we get down to the physics of it.  If you had a torque gauge on the crankshaft it would read the actual "twist" or torque regardless of RPM.  Now, a torque that is output at an RPM is something we can work with and is known as horsepower, newtons, or kilo Watts (in metric). 

 

So, torque is important.  However Torque alone is only half the story of any engine.  The horsepower curve tells the whole story, and we design engines to make the best torque vs rpm (aka: horsepower) curve we can and then gear the vehicle to spend the most time in the best balance of economy and usable power range of that horsepower curve. 

 

csm.. not sure where you are headed with the torque is static. static to me means 'stationary', 'unchanging'.
 

Edited March 3, 2015 by CSM

[rancherman]

ok, I intentionally paid attention to my run out in the hills this weekend, loaded with cattle.

I forced myself to hit the bottom of the hill at 1700, in 5th gear. I told my son to hit the stopwatch, the instant I floored it. It took exactly 6 seconds to lose 200 rpm, forcing me to downshift.

Next hill, I hit at 2600. same thing, he timed me the instant I started up the hill, and floored it. rpm degradation was the same. 3 seconds per 100 rpm loss. I barely made it to the top.

The difference was, I was on the bottom end of the torque curve, and had basically zero - no reserve. I lost my power band within 200 rpm.

I had almost 1000 rpm of 'cush' before the torque fell off, forcing a shift. with the higher start rate.

More 'power'? nope. speed burned off at the same rate...

( I don't ever want to run any vehicle this way ever again.)

So, 'easier to roll through the hills'.... yes and no. Sure was 'easy on me'.. I didn't have to push the clutch in and downshift.

'easier on the engine'?? hmmmmm, jury is out on that one!

CSM, you're right on the length of lever and amount of torque. Your personal hp never changes, but the speed you can turn a shaft with a short handle is much faster than one with a long handle!

The amount of torque you can apply to a shaft is large when you have a long handle, but you can't race around a 30 foot handle fast enough to spin it very fast! LOL, back in physics class, I measured myself,(legs) I had .23 horsepower.. don't laugh!

now, a 3 inch handle is something we can easily spin fairly fast, but we'd feel every little ounce of resistance!

Our 'variable handle' in our engine (not the crankshaft.. it's a fixed throw) is the amount of fuel and air burning above the piston. It can be just enough to allow the engine to idle at 800 rpm, or enough to accelerate our truck up a hill.

[AH64ID]

ok, I intentionally paid attention to my run out in the hills this weekend, loaded with cattle.I forced myself to hit the bottom of the hill at 1700, in 5th gear. I told my son to hit the stopwatch, the instant I floored it. It took exactly 6 seconds to lose 200 rpm, forcing me to downshift.Next hill, I hit at 2600. same thing, he timed me the instant I started up the hill, and floored it. rpm degradation was the same. 3 seconds per 100 rpm loss. I barely made it to the top.The difference was, I was on the bottom end of the torque curve, and had basically zero - no reserve. I lost my power band within 200 rpm.I had almost 1000 rpm of 'cush' before the torque fell off, forcing a shift. with the higher start rate.More 'power'? nope. speed burned off at the same rate...( I don't ever want to run any vehicle this way ever again.).

The fact that the truck slowed the same, assuming that the grades were identical, proves you made more power. The speed you were driving required more power at 2600 rpms. So if your power requirement is higher and your WOT deceleration is the same your power production is higher.

On my truck 1700 is 44mph and 2600 is 67mph, that's a 50% increase in speed which will account for a major power requirement increase.

Using an example from a Cummins fuel mileage secret bulletin the power requirement increase from 45 to 70 is about 170%... So yes, you were making lots more power at 2600 rpms.

 

1700 to 2600, given a flat torque curve, provides about 150% more hp. So you have about a 170% increase in power requirement and a 150% increase in horsepower.. in fact you should have slowed just a little faster as speed too more power.

[Cowboy]

AH64ID

 

I'm not sure if understanding you correctly.

 

Power is the amount of work something can get done.

Torque is the rotational force of something.  whether that be a torque wrench, an engine.  Lots of torque does NOT mean lots of power.

RPM is how fast  something spins.  Again, lots of RPM does NOT mean lots of power.

 

 

We all know (Torque * RPM) / 5252 = Horsepower.

 

Now, what is it that actually pushes the  truck forward.  It's the torque presented to the rear wheels.  So lets say we have two engines.  Both make 800 lb/ft of torque all the way through the RPM range.  Though Engine #1 defuels @ 1700 RPM.  And Engine #2 defuels @ 3400 RPM.  If we do the math, Engine #1 makes 259 peek hp.  And Engine #2 makes 518 peek HP.  

 

Now lets say you load them both with the same amount of weight to where they can barely maintain speed @ 1600 RPM.  We know that they are both are putting down 3280 lb/ft of torque to the wheels (perfect world with no friction loss).  

 

Now, you try and take a hill.  They will both slow down at the same rate.  WHAT!?!?  Well, lets try backing up engine #2 and try taking  the hill again but this time at @ 3200 RPM...   You're still going to decelerate at the same rate.  And the answer is simple, the torque to the wheels is still the same 3280 lb/ft as before.  

So all Engine #2's HP is for nothing?  I mean where did all it's extra power go?!?!?.  Again simple.  Your engine is turning twice the speed, and so your wheels are also.  And because power is torque*speed,  you are making double the power as the first run.

 

Now there is one more thing that we need to remember.  These Engines are also fitted with a transmission, and what a transmission really is, is an "RPM to Torque" converter.   And So it enables us to take #2 Engines extra RPM capability, which would otherwise be useless to us as we're not trying to go any faster, we're just trying to make it up the hill.  And Convert it to useable torque.

 

 With that knowledge, we can take engine #2 for another try up the hill.  But this time, you'll shift the transmission to a 2:1 ratio.  And again we'll be at 3200 RPM.  So we're travelling at the same speed as the first try, but once we hit the hill, we'll have twice the available torque at the wheels.  Which in the end, is what takes us up the hill.

[AH64ID]

 

AH64ID

 

I'm not sure if understanding you correctly.

 

Power is the amount of work something can get done.

Torque is the rotational force of something.  whether that be a torque wrench, an engine.  Lots of torque does NOT mean lots of power.

RPM is how fast  something spins.  Again, lots of RPM does NOT mean lots of power.

 

 

We all know (Torque * RPM) / 5252 = Horsepower.

 

Now, what is it that actually pushes the  truck forward.  It's the torque presented to the rear wheels.  So lets say we have two engines.  Both make 800 lb/ft of torque all the way through the RPM range.  Though Engine #1 defuels @ 1700 RPM.  And Engine #2 defuels @ 3400 RPM.  If we do the math, Engine #1 makes 259 peek hp.  And Engine #2 makes 518 peek HP.  

 

Now lets say you load them both with the same amount of weight to where they can barely maintain speed @ 1600 RPM.  We know that they are both are putting down 3280 lb/ft of torque to the wheels (perfect world with no friction loss).  

 

Now, you try and take a hill.  They will both slow down at the same rate.  WHAT!?!?  Well, lets try backing up engine #2 and try taking  the hill again but this time at @ 3200 RPM...   You're still going to decelerate at the same rate.  And the answer is simple, the torque to the wheels is still the same 3280 lb/ft as before.  

So all Engine #2's HP is for nothing?  I mean where did all it's extra power go?!?!?.  Again simple.  Your engine is turning twice the speed, and so your wheels are also.  And because power is torque*speed,  you are making double the power as the first run.

 

Now there is one more thing that we need to remember.  These Engines are also fitted with a transmission, and what a transmission really is, is an "RPM to Torque" converter.   And So it enables us to take #2 Engines extra RPM capability, which would otherwise be useless to us as we're not trying to go any faster, we're just trying to make it up the hill.  And Convert it to useable torque.

 

 With that knowledge, we can take engine #2 for another try up the hill.  But this time, you'll shift the transmission to a 2:1 ratio.  And again we'll be at 3200 RPM.  So we're travelling at the same speed as the first try, but once we hit the hill, we'll have twice the available torque at the wheels.  Which in the end, is what takes us up the hill.

 

 

 

The torque to the wheels is the same 1600 vs 3200 but as you pointed out the hp is much higher. Higher horsepower with the same torque means the work can get done faster and thus it won't slow the same, load dependent.  As I pointed out if it does slow the same it is an indication of the added power simply from the additional power requirement to be going 2x as fast. If HP didn't matter and TQ was the only important thing then rancherman would have slowed down MUCH faster due to an additional 170% power required to maintain speed on the same hill.

 

There is reason I say find the load that can be held at the higher rpm and see how it does at the lower rpm. This is because you cannot use the rpm governor as a good example when the torque curve is flat. They are both the same engine right up until the 2nd on governs, so if one can't accelerate past 1600 then neither can the other. You have to find a way to demonstrate the additional power at the upper rpm, so you need to get there first.

 

Take 2 identical trucks, and put two different electric motors on the wheel.. no diff, no trans, just a direct drive from the motor. Give them the 3280 ft/lbs of torque we are talking about, but give one of them 400hp and one of them 200hp. See what they do for loads, the 400hp motor will do more work over time.. about 2x as much :-)

 

I was thinking about the large power increase required simply to go from 44 mph to 67 mph, my truck in 5th at the "test" rpms. It's too much to help quantify, as I mentioned around 170% from one Cummins article, compared to only a 150% increase in hp. So a better test would be at a slower speed, with a MUCH heavier trailer. A NV5600 truck with 4.10's in 3rd gear only has a 11 mph split from 1800 to 2500, and at that low of a speed the power difference in minimal (maybe 10%, and very little is aero dynamic). Now the problem with this is in order to find a load where the truck is stable at 2500 rpms WOT in 3rd means a LOT, LOT, LOT of drive-train stress... I don't want to test it, even at a stock tune.. or lower. But at least in 3rd gear you can quantify the 150% increase in horsepower and only a 10% increase in power requirement.

 

 

As you said torque without rpms won't get a lot of work done, no horsepower. Lots of rpms with no hp, or torque, won't get a lot done. But if you have the appropriate tq at the correct rpm you also have the correct hp.

 

I think we talked about it in the other thread, but take 3 different identical trucks. Each one with a different rear end ratio and give them all the same load. Put them on a flat road at 60 mph where they can all maintain speed. All 3 engines are making the same horsepower but different torques. The wheel torque will be identical thou. What does that tell us? That the torque to the wheels tells us how much force is needed to keep them moving at that speed, and the horsepower tells us how fast they can do it which in this case is 60 mph. 3 different rpms, same horsepower. If the torque was the same but the horsepower dropped the speed would drop. It doesn't matter how you look at it.

 

On that same token lets look at a truck that is traveling at 60 mph, and lets assume that the wheel torque required was 800 ft/lbs. Let's look at the different gears, useable-ish ones at 60.. 4-6 (NV5600, 3.73's, 245/70R19.5)

 

Torque Requirement

4th gear 3235 rpms, engine torque required 192.8 ft/lbs

5th gear 2328 rpms, engine torque required 268.1 ft/lbs

6th gear 1699 rpms, engine torque required 367.3 ft/lbs

 

Horsepower Requirement

4th gear 3235 rpms, engine horsepower required 118.8hp

5th gear 2328 rpms, engine horsepower required 118.8hp

6th gear 1699 rpms, engine horsepower required 118.8hp

 

Even gearing doesn't change the horsepower required (I am sure this is nothing new). So this engine needs to be able to make 118.8hp to maintain 60mph with the given load. If the engine can't make 118.8hp it won't be able to do 60 mph in any gear, regardless of the torque capability. An engine rated at 100/400 has the torque to meet all 3 of the gears torque requirements but doesn't have the horespower so the speed could never be reached or held.

 

Why do semi's have advertised horsepower ratings? Because regardless of the gearing the horsepower tells you how fast you can go up a grade, considering they all operate in similar rpm band.  Same thing with boats, hp tells the boat builder how fast one can spin a prop... Same as a helicopter. Since you cannot increase horsepower thru gearing the engine must be able to make the appropriate horsepower for the task at hand.

 

I generally think we are all on about the same page, but some of the terms are different. I love hearing the argument that horsepower is useless, it's torque at the proper rpm that counts... Well what do you think horsepower is???? The above numbers show that perfectly.

[Cowboy]

 

The torque to the wheels is the same 1600 vs 3200 but as you pointed out the hp is much higher. Higher horsepower with the same torque means the work can get done faster and thus it won't slow the same, load dependent.  As I pointed out if it does slow the same it is an indication of the added power simply from the additional power requirement to be going 2x as fast. If HP didn't matter and TQ was the only important thing then rancherman would have slowed down MUCH faster due to an additional 170% power required to maintain speed on the same hill.

 

 

If the Torque at the wheels is the exact same, but the HP at the wheels is double.  Then the wheels are spinning twice as fast.  Which case you may be right, but that seems like more of an argument of aerodynamics rotational mass, and momentum.  Not so much HP vs Torque.

 

 

Take 2 identical trucks, and put two different electric motors on the wheel.. no diff, no trans, just a direct drive from the motor. Give them the 3280 ft/lbs of torque we are talking about, but give one of them 400hp and one of them 200hp. See what they do for loads, the 400hp motor will do more work over time.. about 2x as much :-)

 

The 400hp one would be spinning twice as fast.   Which would mean your speed would be double.  Which would mean they would accelerate together until the 200hp motor runs out of revs.

 

I was thinking about the large power increase required simply to go from 44 mph to 67 mph, my truck in 5th at the "test" rpms. It's too much to help quantify, as I mentioned around 170% from one Cummins article, compared to only a 150% increase in hp. So a better test would be at a slower speed, with a MUCH heavier trailer. A NV5600 truck with 4.10's in 3rd gear only has a 11 mph split from 1800 to 2500, and at that low of a speed the power difference in minimal (maybe 10%, and very little is aero dynamic). Now the problem with this is in order to find a load where the truck is stable at 2500 rpms WOT in 3rd means a LOT, LOT, LOT of drive-train stress... I don't want to test it, even at a stock tune.. or lower. But at least in 3rd gear you can quantify the 150% increase in horsepower and only a 10% increase in power requirement.

 

 

I don't have a perfect test for you, though there was this one route I'd take with about a 45k load.  To get up this one hill, you have to hit it in 3rd, and then there was a short flat spot where you would then down shift to 2nd and get the RPM's to about 2500-2700 and floor it.  The RPMs would then drop until they got around 1800 where it would stay for the last half of the climb.  This is with a 01 nv5600 and 3.54's.

 

On that same token lets look at a truck that is traveling at 60 mph, and lets assume that the wheel torque required was 800 ft/lbs. Let's look at the different gears, useable-ish ones at 60.. 4-6 (NV5600, 3.73's, 245/70R19.5)

 

Torque Requirement

4th gear 3235 rpms, engine torque required 192.8 ft/lbs

5th gear 2328 rpms, engine torque required 268.1 ft/lbs

6th gear 1699 rpms, engine torque required 367.3 ft/lbs

 

Horsepower Requirement

4th gear 3235 rpms, engine horsepower required 118.8hp

5th gear 2328 rpms, engine horsepower required 118.8hp

6th gear 1699 rpms, engine horsepower required 118.8hp

 

Even gearing doesn't change the horsepower required (I am sure this is nothing new). So this engine needs to be able to make 118.8hp to maintain 60mph with the given load. If the engine can't make 118.8hp it won't be able to do 60 mph in any gear, regardless of the torque capability. An engine rated at 100/400 has the torque to meet all 3 of the gears torque requirements but doesn't have the horespower so the speed could never be reached or held.

 

 

That is a excellent example.  The Torque at the wheels required didn't change.  And neither did the speed.  and thus the HP required didn't change.  Cause Like said, and transmission is a RPM to Torque converter. whether it be buck or boost.  And so the HP going in is the same as the HP going out.  But the torque is what changes.  And with the transmission you can take advantage of the HP by putting it in a lower gear.

 

 

I want to thank everyone in this thread.  When I was a kid, I asked my folks "what is the difference between HP and Torque?".  Being home schooled they made an assignment out of it lol.  This is the first time I've been able to discuss this publicly, cause it's one of those topics I wouldn't touch with a ten foot pole on a different forum.  So thank you!

[AH64ID]

If the Torque at the wheels is the exact same, but the HP at the wheels is double.  Then the wheels are spinning twice as fast.  Which case you may be right, but that seems like more of an argument of aerodynamics rotational mass, and momentum.  Not so much HP vs Torque.

 

 

 

 

The 400hp one would be spinning twice as fast.   Which would mean your speed would be double.  Which would mean they would accelerate together until the 200hp motor runs out of revs.

 

 

 

Exactly, it takes 2x the hp to go 2x as fast.

 

Would the 200hp run out of revs or hp? What came first, the chicken or the egg?

 

 

That is a excellent example.  The Torque at the wheels required didn't change.  And neither did the speed.  and thus the HP required didn't change.  Cause Like said, and transmission is a RPM to Torque converter. whether it be buck or boost.  And so the HP going in is the same as the HP going out.  But the torque is what changes.  And with the transmission you can take advantage of the HP by putting it in a lower gear.

 

Yeah the ability to gear down is huge! Increase torque and get the hp required to do the work at the speed desired... it's why both are important and real.

 

 

I want to thank everyone in this thread.  When I was a kid, I asked my folks "what is the difference between HP and Torque?".  Being home schooled they made an assignment out of it lol.  This is the first time I've been able to discuss this publicly, cause it's one of those topics I wouldn't touch with a ten foot pole on a different forum.  So thank you!

 

Lots of FUN!!!

[Mopar1973Man]

If the Torque at the wheels is the exact same, but the HP at the wheels is double.  Then the wheels are spinning twice as fast.  Which case you may be right, but that seems like more of an argument of aerodynamics rotational mass, and momentum.  Not so much HP vs Torque.

 

Here is the rest of that for you.

The Effects of Rotational Inertia on Automotive Acceleration

 

I got to admit this is a awesome thread with plenty of info.

[dorkweed]

 

Edited March 6, 2015 by dorkweed

[dorkweed]

What's needed here (besides a Cummins), HP or torque??

 

[Wild and Free]

What's needed here (besides a Cummins), HP or torque??

 

Ford_20101201195052_reg.png

Robbie knievil ?