Can someone answer this question to help me understand Torque vs. Horsepower

[amdhunter]

I still don't get the relation, all I see is mathematics involved on most of the sites I visit.
So I have a question...[even though these are possibly impossible.] (But I am hoping it will help me understand.)

If I had a car with 1HP + 1000lbs of torque, how would it react when I stepped on the gas?

What about if I had 1000HP + 1lb of torque?

What would be faster in general? A high torque car or a high HP one? Does there always have to be some balance?

 

[Ktulu]

Horsepower = sells cars.

Torque = wins races.

 

[mwmorph]

torque and horsepower are interrelated. Torque is the twisting force while horsepower is the twisting force and the speed at which the shaft is spinning, thus accounting for amount of work done.

Torque is how hard you are pushed back into your seat, horsepower is how long you can keep that feeling going before shifting, when taking torque into account.

for example, 1000lb/ft of torque would give yuo whiplash... for the 1/2ms before you hit your 5.2rpm redline while the 1000hp car would probably never push you backwards but it'll have a hell of a time going anywhere unless you're near the 5.252 million rpm limiter.
What would be faster? Torque is dependent on physical engine displacement. Hp is dependent on high revs, so usually a high hp/low torque engine (such as in F1 racing) is much smaller and lighter, thus making it quicker but if its the same engine and all else being equal, with optimal gearing and driving, etc for each, it should be equal acceleration.

 

[imported_K3N]

when it comes to straight line, you want horsepower, when it comes to corners you want torque. Honestly i'd rather have a car with 250hp/good torque (subaru impreza) than a 500hp with shitty toque(crap handling) (MUSTANG GT500 or any muscle car for that matter). Keep in mind though that suspension also plays a major in a cars cornering abilities. Semi trucks have a high amount torque i believe.

 

[Zenmervolt]

Originally posted by: amdhunter
I still don't get the relation, all I see is mathematics involved on most of the sites I visit.
So I have a question...[even though these are possibly impossible.] (But I am hoping it will help me understand.)

If I had a car with 1HP + 1000lbs of torque, how would it react when I stepped on the gas?

What about if I had 1000HP + 1lb of torque?

What would be faster in general? A high torque car or a high HP one? Does there always have to be some balance?

I've been trying for a long time to find a good way to explain it in layman's terms. I'll have a go at it here again and see if I've gotten any better at it. For those who know the math and such, mind that the explanation here ignores RPM range, gearing, etc and does so intentionally. Note also that terms such as "weight" are used non-scientifically. In other words, this is intentionally simplistic.

Torque is the ability to do work.

Horsepower is the ability to do work quickly.

If two engines have 100 ft-lbs of torque, and but one is 50 hp and the other is 100 hp, they will both be able to move the same amount of weight, but the 100 hp engine will be able to move it twice as fast.

If two engines have 100 hp, but one has 50 ft-lbs of torque and the other has 100 ft-lbs of torque, the second engine will be able to move twice the amount of weight, but will be no faster than the first engine up to the point where the first engine can no longer move the weight. At that point, the first engine will stall, while the second engine will continue to move the weight.

In other words, torque dictates the maximum amount of "weight" that an engine can move, while horsepower dictates how quickly that weight can be moved.

One horsepower is 550 ft-lbs of work per second. That can mean an engine that moves 550 pounds one foot, or an engine that moves 55 pounds 10 feet. This is where RPM comes into play. If an engine is making 550 ft-lbs of torque at 1,000 RPM, it is capable of the same amount of work overall as another engine that makes 55 ft-lbs of torque at 10,000 RPM. Note also that both engines are making exactly the same horsepower now (one just makes that horsepower at 1,000 RPM, while the other needs to be spinning at 10,000 RPM).

However, as long as that 55 ft-lbs is enough force to make the engine's load move, the second engine will be faster overall, but if the engine's load is greater than 55 ft-lbs, the second engine will stall, while the first engine will continue blithely on.

In practice, however, torque can be multiplied by gearing, while horsepower cannot, so if we then attach a transmission to that second, 55 ft-lb engine, and gear it down so that the output of the transmission is 1,000 RPM when the engine RPM is 10,000, the net result is now exactly the same as the engine with 550 ft-lbs at 1,000 RPM.

In practice, it's more important to have a broad torque curve and a wide powerband. If torque drops off steeply after 2,500 RPM (like it does with the diesel engines in semis) then you need to have many gears in order to get up to speed (some semis have 21-speed transmissions), and you also lose the advantage of the gearing as soon as you shift.

Again taking two engines, one that makes 100 ft-lbs from idle to 5,000 RPM (redline) and another that makes 50 ft-lbs from idle to 7,000 RPM (redline). If we make the gearing for the first engine such that it multiplies torque to match the first engine's output, they will launch equal, and stay side-by-side, until the second engine hits redline. Because of gearing, when the second engine hits redline, the first engine is only turning 3,500 RPM and can continue to accelerate at the same rate. The second engine, however, must up-shift, which reduces the torque available at the wheels because the gearing advantage is reduced. Once the first engine shifts gears, it starts to fall behind the torquier engine.

Looking at this now, I think it might be more confusing, but I'll see how its received.

ZV

 

[Pacfanweb]

^sounds good to me.

You see a lot of opinions on this topic. Google "torque vs HP" or something similar, and there a quite a few sites that have good explanations, also.

 

[GoatMonkey]

Originally posted by: K3N
when it comes to straight line, you want horsepower, when it comes to corners and tight turns you want torque. Honestly i'd rather have a car with 250hp/good torque (subaru impreza) than a 500hp with shitty toque(crap handling) (MUSTANG GT500 or any muscle car for that matter). Keep in mind though that suspension also plays a major in a cars cornering abilities. Semi trucks have a high amount torque i believe.

Torque has nothing to do with handling, unless you count torque steer in front drive cars.

 

[Tiamat]

Originally posted by: Zenmervolt

Originally posted by: amdhunter
I still don't get the relation, all I see is mathematics involved on most of the sites I visit.
So I have a question...[even though these are possibly impossible.] (But I am hoping it will help me understand.)

If I had a car with 1HP + 1000lbs of torque, how would it react when I stepped on the gas?

What about if I had 1000HP + 1lb of torque?

What would be faster in general? A high torque car or a high HP one? Does there always have to be some balance?

I've been trying for a long time to find a good way to explain it in layman's terms. I'll have a go at it here again and see if I've gotten any better at it. For those who know the math and such, mind that the explanation here ignores RPM range, gearing, etc and does so intentionally. Note also that terms such as "weight" are used non-scientifically. In other words, this is intentionally simplistic.

Torque is the ability to do work.

Horsepower is the ability to do work quickly.

If two engines have 100 ft-lbs of torque, and but one is 50 hp and the other is 100 hp, they will both be able to move the same amount of weight, but the 100 hp engine will be able to move it twice as fast.

If two engines have 100 hp, but one has 50 ft-lbs of torque and the other has 100 ft-lbs of torque, the second engine will be able to move twice the amount of weight, but will be no faster than the first engine up to the point where the first engine can no longer move the weight. At that point, the first engine will stall, while the second engine will continue to move the weight.

In other words, torque dictates the maximum amount of "weight" that an engine can move, while horsepower dictates how quickly that weight can be moved.

One horsepower is 550 ft-lbs of work per second. That can mean an engine that moves 550 pounds one foot, or an engine that moves 55 pounds 10 feet. This is where RPM comes into play. If an engine is making 550 ft-lbs of torque at 1,000 RPM, it is capable of the same amount of work overall as another engine that makes 55 ft-lbs of torque at 10,000 RPM. Note also that both engines are making exactly the same horsepower now (one just makes that horsepower at 1,000 RPM, while the other needs to be spinning at 10,000 RPM).

However, as long as that 55 ft-lbs is enough force to make the engine's load move, the second engine will be faster overall, but if the engine's load is greater than 55 ft-lbs, the second engine will stall, while the first engine will continue blithely on.

In practice, however, torque can be multiplied by gearing, while horsepower cannot, so if we then attach a transmission to that second, 55 ft-lb engine, and gear it down so that the output of the transmission is 1,000 RPM when the engine RPM is 10,000, the net result is now exactly the same as the engine with 550 ft-lbs at 1,000 RPM.

In practice, it's more important to have a broad torque curve and a wide powerband. If torque drops off steeply after 2,500 RPM (like it does with the diesel engines in semis) then you need to have many gears in order to get up to speed (some semis have 21-speed transmissions), and you also lose the advantage of the gearing as soon as you shift.

Again taking two engines, one that makes 100 ft-lbs from idle to 5,000 RPM (redline) and another that makes 50 ft-lbs from idle to 7,000 RPM (redline). If we make the gearing for the first engine such that it multiplies torque to match the first engine's output, they will launch equal, and stay side-by-side, until the second engine hits redline. Because of gearing, when the second engine hits redline, the first engine is only turning 3,500 RPM and can continue to accelerate at the same rate. The second engine, however, must up-shift, which reduces the torque available at the wheels because the gearing advantage is reduced. Once the first engine shifts gears, it starts to fall behind the torquier engine.

Looking at this now, I think it might be more confusing, but I'll see how its received.

ZV

Sounds pretty good to me, thanks!

 

[ayabe]

Originally posted by: K3N
when it comes to straight line, you want horsepower, when it comes to corners you want torque. Honestly i'd rather have a car with 250hp/good torque (subaru impreza) than a 500hp with shitty toque(crap handling) (MUSTANG GT500 or any muscle car for that matter). Keep in mind though that suspension also plays a major in a cars cornering abilities. Semi trucks have a high amount torque i believe.

I'm pretty sure that a GT500 makes more torque throughout it's powerband than my WRX does at it's peak, I'm not sure what you are talking about.

To Zemmervolt, awesome writeup man.

 

[Summitdrinker]

we went over this topic here about 5 months ago ............................

 

[Demon-Xanth]

It's all about the curves really. You can't have HP without torque nor RPM.

When it comes down to most discussions though, it's what has the most torque in the RPM range that you're going to be needing it. Truckers don't want an engine that's up around redline all the time. They need the torque at a lower RPM and they need it all day long. F1 drivers don't need the torque down low, they trade off for a higher RPM engine that has high power with little torque.

Why do they do this? The same reason why power companies transmit over high voltage and low current. To handle torque you need large components, to handle power you need good techniques.

F1 has weight as the primary concern and longevity very far back. They spend money on very light weight parts and good bearings. They're not going to leave it running 24/7 in freezing weather. It's going to be on a track for an hour or so. So they don't mind the parts spinning like mad and keeping everything stressed. And efficiency is never a major concern for F1 engines.

Which when you go back to truckers, 1MPG gain for them can mean another $5,000/year in their pockets. They're already moving 80,000LBs, having an engine that weighs 2000LBs isn't an issue. They already need large parts to handle the weight, so large shafts in those large axles just comes naturally.

Now where does the passenger car fit in? Somewhere in the middle. Most engines weigh between 300 and 600LBs (yes, even the 4 cylinders...) and what they're tuned for largely depends on where they fit in. The S2000 engine in a large sedan would be just flat out awkward while a large sedan's engine in an S2000 would make it a boring car. There's no such thing as having everything

 

[LS21]

as purely a numbers issue, the HP figure is more representative of a car's speed

just follow the below line by line and you'll see it

-torque is the actual twisting force.
-torque is generated by the motor... (crankshaft --> flywheel)
-torque is transferred THROUGH transmission TO THE WHEELS
(the transmission is where its lost on some people: )
-gearing (different-sized cogs) allows for mechanical leverage... aka "torque multiplication" ... torque at wheels = torque produced by motor * gearing

so to get actual force for acceleration, you need a "short" gear, that gives a high multiplier. you will only need little torque from the motor (input) , multiplied through the transmission, to boost the torque at the wheels (output). the trade-off to a short gear is that now you need to turn the motor lots and lots of time to get some revolution at the wheels.

ie. on a 10sp bicycle, if you use a "short" gear, you can accelerate really quickly, but you have to pedal a lot. on a "taller" gear, it becomes more difficult to pedal, but you dont have to pedal as frequently to get lots of rotation of the wheels.

so you can get lots of torque at the wheel with short gearing, but you'll need the motor to be able to spin fast (and produce enough torque at that high rate of spin). if the motor cant spin any faster, to continue gaining ground speed, you need to change to a gear with "taller" ratio. now you have a smaller multiplier, which means less torque AT THE WHEELS...

Torque at wheels for acceleration = Low Motor Torque * Short Gear = High Motor Torque * Tall Gear

-to keep the same ground speed, the smaller motor must be able to maintain high revs... so a high-torque motor that spins slow, produces the same output as a low-torque motor that spins fast.... HP being a multiplicative function of torque, is a number that better represents this output.

generalizations: larger displacement motors generally produce more torque.... BUT larger displacement motors generally spin lower. (larger pistons/long stroke/more mass).

so the 2 approaches for making a fast car is a small, high-revving motor, or a large motor (and of course if you make a large high-revving motor (Ferrari / Z06)) then youre ACE.

on paper, the HP and torque figure is just a PEAK figure, at 1 instance in time. but unless the engine has a peaky characteristic, that singular HP/Torque figure is plenty indicative. #HP is ~ the output of the motor. #Torque is the approach (small fast vs large slow). Hence cars compared in performance with the HP:WEIGHT RATIO, never Torque:Weight




Summary: just looking at the numbers, more HP = fast. more TQ = not necessary fast.

 

[Vic]

Great write-up from Zen earlier. My $0.02:

hp = (tq * rpm)/5252


The constant 5252 is not a mystery number, but comes from the definition of hp itself, which is 1 hp = 33,000 ft/min. 5252 = 33,000 / 2p (radians)

Therefore, hp is a measurement of the speed at which torque is produced, and nothing more. It is not separate from torque nor in opposition to torque. One doesn't take you into the wall while the other pushes you through it or any of that BS.

If you have an engine making 200 lb-ft at 2000 rpm, that's 76 hp. If it's still doing the same 200 lb-ft at 6000 rpm, that's 228 hp.
Why more power with the same torque? Because the engine internals, which always travel the same distances with each and every revolution, are traveling faster speeds at high rpm in order to cover those same distances in less time, all the while still exerting the same twisting force with its potential for even greater speed.

Not convinced? Let's use a simple example of 25" diameter tires, 3:1 diff ratio, and 1:1 gear ratio.
At 2000 rpm, that's almost 48 mph. Using the numbers above, the engine would be exerting 200 lb-ft of twisting force at 48 mph.
At 6000 rpm, that's 143 mph. The engine is exterting that same 200 lb-ft at 143 mph.
Which is more impressive?

And that's why hp as a measurement is important, and wins races.

 

[LS21]

Originally posted by: Vic
Therefore, hp is a measurement of the speed at which torque is produced, and nothing more. It is not separate from torque nor in opposition to torque. One doesn't take you into the wall while the other pushes you through it or any of that BS.




And that's why hp as a measurement is important, and wins races.

x5 billion. especially in light of people throwing around shelby's misleading, likely out-of-context quote

 

[imported_Truenofan]

just read what ZV wrote. its right.

 

[Raduque]

Originally posted by: K3N
when it comes to straight line, you want horsepower, when it comes to corners you want torque. Honestly i'd rather have a car with 250hp/good torque (subaru impreza) than a 500hp with shitty toque(crap handling) (MUSTANG GT500 or any muscle car for that matter). Keep in mind though that suspension also plays a major in a cars cornering abilities. Semi trucks have a high amount torque i believe.

The bolded is the only part you got right, and I'm quite suprised you managed that.

The rest is epic fail.



I've always heard it as "Torque gets you going, horsepower keeps you going".

 

[Demon-Xanth]

Originally posted by: Raduque

Originally posted by: K3N
when it comes to straight line, you want horsepower, when it comes to corners you want torque. Honestly i'd rather have a car with 250hp/good torque (subaru impreza) than a 500hp with shitty toque(crap handling) (MUSTANG GT500 or any muscle car for that matter). Keep in mind though that suspension also plays a major in a cars cornering abilities. Semi trucks have a high amount torque i believe.

The bolded is the only part you got right, and I'm quite suprised you managed that.

The rest is epic fail.



I've always heard it as "Torque gets you going, horsepower keeps you going".

Well, in a semi's credit, lets see an Enzo take a corner while towing 50 tons

...okay, lets go for a Miata instead. I don't want to see another great and rare car die a pointless death.

 

[brunell8]

You have obviously never driven or been a passenger in a modified Fiero. My last one had a 3800 Series II N/A, and it would scream. And that is not the engine of choice - most prefer either the supercharged 3800, a Northstar, or an SBC.

Originally posted by: Demon-Xanth
The S2000 engine in a large sedan would be just flat out awkward while a large sedan's engine in an S2000 would make it a boring car. There's no such thing as having everything

 

[thedarkwolf]

Originally posted by: Demon-Xanth

Now where does the passenger car fit in? Somewhere in the middle. Most engines weigh between 300 and 600LBs (yes, even the 4 cylinders...) and what they're tuned for largely depends on where they fit in. The S2000 engine in a large sedan would be just flat out awkward while a large sedan's engine in an S2000 would make it a boring car. There's no such thing as having everything

S2000 engine in large sedan = crap but say a Chevy LSx series v8 in a S2000 sure as hell wouldn't make it a boring car. I guess it depends on what large sedan engine you are talking about.

 

[Demon-Xanth]

Originally posted by: brunell8
You have obviously never driven or been a passenger in a modified Fiero. My last one had a 3800 Series II N/A, and it would scream. And that is not the engine of choice - most prefer either the supercharged 3800, a Northstar, or an SBC.

Originally posted by: Demon-Xanth
The S2000 engine in a large sedan would be just flat out awkward while a large sedan's engine in an S2000 would make it a boring car. There's no such thing as having everything

Considering that both of the Fiero's optional engines were also in mid-sized Sedans...

But yeah, I've heard how easy Northstars fit in. It's pretty much a subframe, add a set of Viper half shafts and you're good to go.

What I was referring to is something like Toyota's 3L V6. A slower revving, uninspired engine vs. the S2000's high strung engine. Then again, there was a guy who stuck both a 2.4L DSM engine and a 500 Caddy into a Yugo. (yes, both at once)

 

[Jahee]

Funny you should ask..!

http://forums.anandtech.com/me...ab=arc&highlight_key=y

 

[thedarkwolf]

Originally posted by: Demon-Xanth

Originally posted by: brunell8
You have obviously never driven or been a passenger in a modified Fiero. My last one had a 3800 Series II N/A, and it would scream. And that is not the engine of choice - most prefer either the supercharged 3800, a Northstar, or an SBC.

Originally posted by: Demon-Xanth
The S2000 engine in a large sedan would be just flat out awkward while a large sedan's engine in an S2000 would make it a boring car. There's no such thing as having everything

Considering that both of the Fiero's optional engines were also in mid-sized Sedans...

But yeah, I've heard how easy Northstars fit in. It's pretty much a subframe, add a set of Viper half shafts and you're good to go.

What I was referring to is something like Toyota's 3L V6. A slower revving, uninspired engine vs. the S2000's high strung engine. Then again, there was a guy who stuck both a 2.4L DSM engine and a 500 Caddy into a Yugo. (yes, both at once)

That wasn't a DSM 2.4l it it was a 2.2l turbo dodge engine but yeah

 

[lurk3r]

This is a massive oversimplification, but you can think of torque as a snapshot of the horsepower if you set the rpm. The problem is there is no good way to measure torque, but horsepower is fairly easy.

Ideally what you want is a nice flat torque curve, with high torque near the minimum rpm range. Typically the bigger V8's and V10's will produce more stable, and higher torque curves, with fairly low hp, since they have so much rotating weight to spin, while 4 cylinder's are usually turbocharged, and capable of running at much higher rpm's, therefore produce more hp, with a crappy torque curve.

A high revving V8 will run at 7000rpm, typically under 5000, while most 4 cylinders rev happily out to 7000, and up to 9000 fairly easily

 

[exdeath]

Originally posted by: lurk3r
This is a massive oversimplification, but you can think of torque as a snapshot of the horsepower if you set the rpm. The problem is there is no good way to measure torque, but horsepower is fairly easy.

Ideally what you want is a nice flat torque curve, with high torque near the minimum rpm range. Typically the bigger V8's and V10's will produce more stable, and higher torque curves, with fairly low hp, since they have so much rotating weight to spin, while 4 cylinder's are usually turbocharged, and capable of running at much higher rpm's, therefore produce more hp, with a crappy torque curve.

A high revving V8 will run at 7000rpm, typically under 5000, while most 4 cylinders rev happily out to 7000, and up to 9000 fairly easily

Torque is a force what is measured directly by determining the measured angular acceleration of a known load or mass.

Horsepower, is just that, power. It's power, a measure of work applied over time. Only by accumulating the measures of a force (of the crank) over a distance (Revolutions) and time (Per Minute) can you calculate horsepower.

And what you say comparing 8 cyls and 4 cyls and relating them to torque and power production is just flat out wrong.

Formula 1 cars use V8s that rev to 19,000 RPM and make 1000 HP.

Top fuel engines are V8s that rev to 6,000 RPM and make 8,000 HP with all that "rotating weight to spin".

Contrast: I know of no 4 cyl engine commonly known to rev to 19,000 RPM OR make 8,000 HP.

 

[Demon-Xanth]

Originally posted by: exdeath


Torque is a force what is measured directly by determining the measured angular acceleration of a known load or mass.

Horsepower, is just that, power. It's power, a measure of work applied over time. Only by accumulating the measures of a force (of the crank) over a distance (Revolutions) and time (Per Minute) can you calculate horsepower.

And what you say comparing 8 cyls and 4 cyls and relating them to torque and power production is just flat out wrong.

Formula 1 cars use V8s that rev to 19,000 RPM and make 1000 HP.

Top fuel engines are V8s that rev to 6,000 RPM and make 8,000 HP with all that "rotating weight to spin".

Contrast: I know of no 4 cyl engine commonly known to rev to 19,000 RPM OR make 8,000 HP.

Here's one that's close to it. 17-18,000RPM:
http://en.wikipedia.org/wiki/Yamaha_YZF-R6