Torque vs Horsepower

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Originally Posted by KrisZ
Originally Posted by ZeeOSix
Originally Posted by KrisZ
If torque by itself is not important, then why is it that most engine designs seek to have the torque curve as flat as possible? Ideally you don't want it to be a curve at all, but rather a nice flat horizontal line.


Because a flat torque curve will result in a nice linearly increasing HP curve. Flat torque curves are achieved by making the engine volumetric efficiency (VE) as high and as constant as possible over the RPM range.


Yes, that's correct. I posed the question to the person claiming torque by itself is not important.

Fact us that torque is the only thing we can measure, so the only way to know the power curve is to measure the torque curve. So it is essential to proper engine tuning.


Torque is measured if using a loaded dyno controlling the engine to a set acceleration rate. Horsepower is then calculated from the torque curve. An inertia dyno measures work (horsepower) by measuring how quickly the engine can accelerate a weighted drum. Torque is then calculated from the horsepower curve.

An old saying around the racing community is "Horsepower sells cars, but torque wins races" which comes from a lack of understanding. When you increase torque at any given rpm range, you also increase the horsepower in that range. The extra horsepower is what increases the acceleration rate through that range, not the torque.
 
Originally Posted by RDY4WAR
Originally Posted by KrisZ
Originally Posted by ZeeOSix
Originally Posted by KrisZ
If torque by itself is not important, then why is it that most engine designs seek to have the torque curve as flat as possible? Ideally you don't want it to be a curve at all, but rather a nice flat horizontal line.


Because a flat torque curve will result in a nice linearly increasing HP curve. Flat torque curves are achieved by making the engine volumetric efficiency (VE) as high and as constant as possible over the RPM range.


Yes, that's correct. I posed the question to the person claiming torque by itself is not important.

Fact us that torque is the only thing we can measure, so the only way to know the power curve is to measure the torque curve. So it is essential to proper engine tuning.


Torque is measured if using a loaded dyno controlling the engine to a set acceleration rate. Horsepower is then calculated from the torque curve. An inertia dyno measures work (horsepower) by measuring how quickly the engine can accelerate a weighted drum. Torque is then calculated from the horsepower curve.

An old saying around the racing community is "Horsepower sells cars, but torque wins races" which comes from a lack of understanding. When you increase torque at any given rpm range, you also increase the horsepower in that range. The extra horsepower is what increases the acceleration rate through that range, not the torque.


Sounds like both methods measure the same thing, an acceleration rate against a mass that is controlled differently. From there the power and torque can be calculated.
 
Originally Posted by 4WD
Ok, how force is related to momentum in the general driveline question - the example I replied to was hitting a wall - impact force.

I got what you meant; you were clear that way. I was just being pedantic about the math.
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When I'm messing around with such things, I do it all algebraically (or use derivatives or integrals or whatever the case requires) and stick to SI base units. It's so much easier to catch something derailing that way. If I had to use Imperial/U.S. units, I'd probably through my calculator against the wall as hard as I could, or, at least, throw it under the wheels of someone doing a HP test on a dyno!
 
Less than an hour ago i made a post about this and it didn't show up (too many quotes, just found out).


Inertia dynos can only estimate hp and calculate tq off of that. They are good for hp capped racing to test the cars against each other on but they have their flaws and should not be tuned on at all. When you see a shop with an inertia dyno you probably want to leave because if they are willing to blow over $30k on a tool that is the wring one for the job (tuning) I dont want them messing with my ecu.
 
Originally Posted by KrisZ
Originally Posted by RDY4WAR


Torque is measured if using a loaded dyno controlling the engine to a set acceleration rate. Horsepower is then calculated from the torque curve. An inertia dyno measures work (horsepower) by measuring how quickly the engine can accelerate a weighted drum. Torque is then calculated from the horsepower curve.

An old saying around the racing community is "Horsepower sells cars, but torque wins races" which comes from a lack of understanding. When you increase torque at any given rpm range, you also increase the horsepower in that range. The extra horsepower is what increases the acceleration rate through that range, not the torque.


Sounds like both methods measure the same thing, an acceleration rate against a mass that is controlled differently. From there the power and torque can be calculated.


Most testing done on engine dynamometers in the heavy duty business is done at constant speed, so observed torque is just what is read on the gauge. If transient testing is done, then a factor correcting torque has to be included that includes the engine acceleration rate. For this factor to be accurate, the total rotational inertia of the engine, driveshaft, and dynamometer must be known.

An inertia chassis dynamometer (DynoJet) only measures the rate of acceleration of the drum, where the moment of inertia is known. Then calculating torque is accomplished by the equation Torque = (moment of inertia) x (angular acceleration rate). Power is calculated at every datapoint by the average rotational speed of the drum during the sampling interval of the datapoint. To calculate the engine power at the flywheel based on chassis dyno data, it is necessary to know the moment of intertia of the complete vehicle driveline, and the mechanical efficiency of the driveline. Good luck with that.
 
Possibly, I`ll see if I can find the source. Can`t remember the first publication it was mentioned in but the second was a Motors Manual, this being 40+ years ago.
 
HP is how fast you're going when you hit a wall...torque is how far you drag the wall after you hit it...
 
Low end torque is what makes a vehicle fun to drive...good example...today's 6 cylinder Mustangs produce over 300 HP and they are actually pretty fast when the engine is wound up, but they can barely get out of their own way at low RPMs...compare that with an LS1 Vette, which makes gobs of low end grunt, which means it goes when you step on it from pretty much any RPM...
 
Some of you are still thinking only in terms of peak power and peak torque. Yes, peak power determines the top speed, but even in racing it's not as important as the rate of acceleration.


Here is pretty much a perfect torque "curve", which is a straight horizontal line right from 0 rpm to maximum. It's a perfect hypothetical scenario and as you can see the power increases in a nice and linear fashion. What this means in terms of acceleration, is that the acceleration rate will be constant throughout the RPM range. This pretty much is a perfect engine/motor for everything from everyday commuting to racing.

[Linked Image]



Compare the above with an LS1 and eventhough the torque curve is pretty flat, the power increase with RPM starts to taper off and really starts to flatten above 5k RPM. This means the acceleration rate also starts to decrease. So you don't have a constant acceleration rate, but a decreasing one as the RPM climb.

[Linked Image]



Thia is why engineers seek out methods of increasing volumetric efficiency and flattening that torque curve because it will mean a more constant increase in power and thus a more constant acceleration rate.

Basically torque makes power, no other way around it and therefore it is crucial for any engine design.
 
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Wow, this thread is really going on for a long time... Here's how I think of torque and horsepower.

Torque: Think of a torque wrench... think of one that is 1 foot long and you're testing it out on a bolt that is locked in a vise and you put a 5 lb weight on the end. Next you put a 20 lb weight on the end.
There is more potential to turn the bolt when 20 lbs is applied.

In the examples above the torque is force x distance or, 1 foot x 5 lbs and 1 foot x 20 lbs.

Next, instead of a bolt locked in a vise, imagine there is bolt that will turn but has a constant resistance. Assume the wrench with 5 lbs can barely turn the bolt and the 20 lb wrench can turn it easily. Since we said the bolt has constant resistance, you must constantly apply that 20 lb force to keep the bolt turning.

Now look at simple math. Torque is Force x Distance and horsepower is just Torque divided by time. In other words, HP = (Force x Distance) / Time.

Time is the important factor here. It's great if your arm is strong enough to momentarily apply 20 ft lbs of torque to the wrench then stop. Do you have enough energy and endurance to continuously apply that 20 ft lbs for say 1 minute or 2 minutes -or 30 minutes?

In other words, Horsepower is just the rate at which you are able to apply a given amount of Torque. This is the fundamental relationship between the two.

It gets confusing because lot's of people here are showing torque/horsepower curves from engines. The issue there, is that engines do not supply constant amounts of torque or horsepower because of their mechanical design. Things change with the engine RPM. If you take any single point on that graph it means that if you held the engine at that RPM, it would be able supply that given amount of torque for the whole time you keep the engine at that RPM.

This is how I think of torque and horsepower... Hope it helps you...

Ray
 
Originally Posted by RayCJ

It gets confusing because lot's of people here are showing torque/horsepower curves from engines. The issue there, is that engines do not supply constant amounts of torque or horsepower because of their mechanical design. Things change with the engine RPM. If you take any single point on that graph it means that if you held the engine at that RPM, it would be able supply that given amount of torque for the whole time you keep the engine at that RPM.

This is how I think of torque and horsepower... Hope it helps you...

Ray



While your explanation of torque and power is spot on, the quoted text is a bit off.

The reason torque and power graphs are important is because power is directly related to torque and RPM and it is changing, that's the whole point of a graph. To show how it is changing throught the RPM range. Peak power and torque figures are quite useless on the other hand.

Here is another graph, sorry about that. But which engine do you think would accelerate faster despite both being rated at peak 150hp and in the exact same setup overall?


[Linked Image]
 
Originally Posted by KrisZ
Originally Posted by RayCJ

It gets confusing because lot's of people here are showing torque/horsepower curves from engines. The issue there, is that engines do not supply constant amounts of torque or horsepower because of their mechanical design. Things change with the engine RPM. If you take any single point on that graph it means that if you held the engine at that RPM, it would be able supply that given amount of torque for the whole time you keep the engine at that RPM.

This is how I think of torque and horsepower... Hope it helps you...

Ray



While your explanation of torque and power is spot on, the quoted text is a bit off.

The reason torque and power graphs are important is because power is directly related to torque and RPM and it is changing, that's the whole point of a graph. To show how it is changing throught the RPM range. Peak power and torque figures are quite useless on the other hand.

Here is another graph, sorry about that. But which engine do you think would accelerate faster despite both being rated at peak 150hp and in the exact same setup overall?

[Linked Image]




I think there was some misunderstanding... In no way did I say that torque curves were not important. Your follow-up reply is taking a turn away from a basic explanation of what torque and horsepower are, which was the point of my post. I'll just mention there is nothing at all off about any of the statements I made. -Period.
 
Originally Posted by RayCJ
If you take any single point on that graph it means that if you held the engine at that RPM, it would be able supply that given amount of torque for the whole time you keep the engine at that RPM.


Only at wide open throttle of course.
 
Originally Posted by KrisZ
Here is pretty much a perfect torque "curve", which is a straight horizontal line right from 0 rpm to maximum. It's a perfect hypothetical scenario and as you can see the power increases in a nice and linear fashion.

[Linked Image]



I've seen some Mustang supercharged Coyote graphs that have a very flat torque curve and resulting linear HP curve, 700 rear wheel HP all the way to redline. Something like that must pull like crazy.
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Edit, here's a couple examples:
https://www.mustang6g.com/forums/threads/5-0-dyno-chart-compilation.49398/page-15#post-2325411

https://www.mustang6g.com/forums/threads/5-0-dyno-chart-compilation.49398/page-17#post-2417516
 
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Originally Posted by ZeeOSix

Originally Posted by RayCJ
If you take any single point on that graph it means that if you held the engine at that RPM, it would be able supply that given amount of torque for the whole time you keep the engine at that RPM.


Only at wide open throttle of course.


No. At any point along the line -not necessarily at WOT.

If you look at that graph posted above (Labeled: 150 Horsepower Advantage) for example say the YAMAHA 4S engine (the black line), at 4000 RPM, it's making 130 HP. That graph does not show torque lines but if it did, there would be a corresponding torque value -and it too would be constant at that RPM. Now, let's put a governor on that engine so it holds the speed at 4000 RPM. In this case, you could now connect a generator head to that engine and supply approximately 745 x 130 (~97k) Watts of power. [There are roughly 745 Watts per horsepower -not counting for efficiency losses].

Of this is a fictitious example because generators in the US typically run at 1800 or 3600 RPM -and nobody in their right mind would run a gas engine at 4000 RPM to power a generator. The concept is 100% accurate -I assure you of that.

Absolutely... at any point along the line of a HP/Torque curve, the corresponding values remain constant at that particular RPM. If not, the graph would be totally meaningless.

Ray
 
When you hold an engine at part throttle, the air flow and harmonics is restricted, and the power curve shifts down to lower rpm. It would be the same as if you were at wide open throttle with a really small throttle body. An engine making peak torque around 4000 rpm at wide open throttle may make peak at only 2500 rpm at 1/4 throttle. Of course that torque number would be far lower as well.
 
I'm buying a supercharged vehicle and with bolt ons / dyno tune I'd like to see a 1 sec reduction in quarter mile times.

HP & torque numbers are only good for dyno bragging....
 
Originally Posted by RayCJ
Originally Posted by ZeeOSix
Originally Posted by RayCJ
If you take any single point on that graph it means that if you held the engine at that RPM, it would be able supply that given amount of torque for the whole time you keep the engine at that RPM.

Only at wide open throttle of course.

No. At any point along the line -not necessarily at WOT.


ALL dyno graphs of HP and T are at wide open throttle. So you're saying an engine will still produce peak HP revving in neutral with no load and still make peak HP? LOL, not true.

If the engine produces 400 peak HP at WOT at say 5000 RPM, then with no load on the engine it will have a cracked open throttle at 5000 RPM and be producing about 20 HP. As the load goes down, so does the required torque to spin the engine at 5000 RPM ... therefore the HP also goes way down. The HP and T curves go up and down on the plot as a function of throttle opening (ie, load on the engine).
 
Originally Posted by ZeeOSix
... If the engine produces 400 peak HP at WOT at say 5000 RPM, then with no load on the engine it will have a cracked open throttle at 5000 RPM and be producing about 20 HP. As the load goes down, so does the required torque to spin the engine at 5000 RPM ... therefore the HP also goes way down. ....
Huh?! With no load, output (brake) power is zero by definition. If you're talking IHP, that's another matter.
 
Originally Posted by CR94
Originally Posted by ZeeOSix
... If the engine produces 400 peak HP at WOT at say 5000 RPM, then with no load on the engine it will have a cracked open throttle at 5000 RPM and be producing about 20 HP. As the load goes down, so does the required torque to spin the engine at 5000 RPM ... therefore the HP also goes way down. ....
Huh?! With no load, output (brake) power is zero by definition. If you're talking IHP, that's another matter.


Read what I said again - it was an example to get my point across in that post. If you hold the RPM at 5000 in neutral there's still the load from the internal friction of the engine. It still takes a small amount of crank HP to make an engine rotate by itself.
 
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