What does horsepower determine?

[bootymac]

HP sells cars, torque wins races

 

[91TTZ]

Originally posted by: Fox5
For instance, say my car is 1500 pounds, and has 142 horsepower, what exactly does that mean? Can the horsepower be used to determine the maximum speed, or what?

HP = (tq x rpm)/5252

Lots of factors determine performance. There are calculators out there that will give you a rough idea of acceleration and top speed given your car's specs.

HP vs. weight determine acceleration, while HP vs. drag determine the top speed. Weight doesn't affect top speed much at all, since it only increases rolling resistance which doesn't account for much parasitic drag at all compared to wind resistance. Speed record cars at Bonneville use ballast (lead or sand) to weigh the car down, since they need to keep the car on the ground and using a wing will create too much aerodynamic drag.

 

[Pacfanweb]

Originally posted by: infestedgh0st

Originally posted by: Pacfanweb

Originally posted by: infestedgh0st

Originally posted by: ElFenix
horsepower is nothing more than torque at a high rpm. it means you don't have to shift as much.

the manufacturers put emphasis on hp because power figures aren't changed by the lever action of a transmission, while torque, as a type of force, is. so, each time you change gears your torque at the wheels is changing, but your horsepower isn't. which is why you accelerate harder in first gear than any other.

actually, hp = torque x rpm / 5252, which means when u rev ur engine hp does change.

hp + gearing matters more on a racecar. Torque makes everything run; excessive torque makes everythign smooth.

Wrong. Once again, HP and Torque are NOT mutually exclusive. Gearing and weight matters to every single vehicle made.
You can't have HP without torque.

obviously, the equation shows that they are NOT mutually exlusive. If torque = 0 then u can't have hp. hp is the measurement of how much work can be done with the torque from the engine at this rpm. Basically the higher you rev, the more hp u get. Torque however has its own torque curve.

Sort of. But you can't just rev an engine higher and higher and keep getting more and more horsepower. Other factors come into play, like how much the heads can flow.
In a perfect world, you could just spin the engine as high as you wanted to whenever you wanted more power, but many other limiting factors prevent this.
That's why there are bigger engines and smaller engines; Depends on what you're trying to do with it.
There is a limit, with car sized engines, to how much torque/hp you can get at a specific rpm. Bigger engines have more torque at lower rpms, and therefore they also have more HP at lower rpms, too.
I remember the old Buick 455's that had around 370hp at 4600rpm, but 510 lb/ft of torque at only 2800rpms!! These engines were put in very large cars that were being built at the time.
It is impossible to get 510 lb/ft of torque out of a naturally aspirated small block at that rpm. The engine just doesn't move enough air to do it. You also aren't going to get 370hp at only 4600 rpm, either. A smaller engine will have to spin higher to get that kind of HP, and will have a lower torque peak as a result.

Again, it just depends on what application you want to put the engine to work in. But more torque is always desireable. If race cars like Nascar or F1 could build engines that has so much torque that they only needed to turn 4000 rpms to move the cars as fast as they needed to go, they would. But that is impossible, so they build/gear them to suit their particular needs, based on the limitations of their respective rules.

Example: Nascar uses 358 cid engines max (give or take an inch) but if they could build a 500 cid engine with the same power, it would have more torque because the peak would be at a lower rpm...and would be a more reliable powerplant as a result, because a larger engine wouldn't need to be as heavily modified to get the same power as the smaller one.

 

[91TTZ]

Good post, pac.

That's why it annoys me when I hear a racerboy with no knowledge of engines say crap like, "yeah, the LS7 makes 500 hp but it needs 7 liters to do it! Hondas engines can rev to 9000 rpm!". Like you said, having to rev high is only a means to an end, it isn't the end, HP and a nice torque curve is.

 

[Demon-Xanth]

1600LBs==1970 VW Beetle.

 

[JoLLyRoGer]

If you have a one pound weight bolted to the floor, and try to lift it with one pound of force (or 10, or 50 pounds), you will have applied force and exerted energy, but no work will have been done. If you unbolt the weight, and apply a force sufficient to lift the weight one foot, then one foot pound of work will have been done. If that event takes a minute to accomplish, then you will be doing work at the rate of one foot pound per minute. If it takes one second to accomplish the task, then work will be done at the rate of 60 foot pounds per minute, and so on.
In order to apply these measurements to automobiles and their performance (whether you're speaking of torque, horsepower, newton meters, watts, or any other terms), you need to address the three variables of force, work and time.

Awhile back, a gentleman by the name of Watt (the same gent who did all that neat stuff with steam engines) made some observations, and concluded that the average horse of the time could lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 foot pounds per second, or 33,000 foot pounds per minute, for an eight hour shift, more or less. He then published those observations, and stated that 33,000 foot pounds per minute of work was equivalent to the power of one horse, or, one horsepower.

Everybody else said OK.

For purposes of this discussion, we need to measure units of force from rotating objects such as crankshafts, so we'll use terms which define a *twisting* force, such as foot pounds of torque. A foot pound of torque is the twisting force necessary to support a one pound weight on a weightless horizontal bar, one foot from the fulcrum.

Now, it's important to understand that nobody on the planet ever actually measures horsepower from a running engine. What we actually measure (on a dynomometer) is torque, expressed in foot pounds (in the U.S.), and then we *calculate* actual horsepower by converting the twisting force of torque into the work units of horsepower.

Visualize that one pound weight we mentioned, one foot from the fulcrum on its weightless bar. If we rotate that weight for one full revolution against a one pound resistance, we have moved it a total of 6.2832 feet (Pi * a two foot circle), and, incidently, we have done 6.2832 foot pounds of work.

OK. Remember Watt? He said that 33,000 foot pounds of work per minute was equivalent to one horsepower. If we divide the 6.2832 foot pounds of work we've done per revolution of that weight into 33,000 foot pounds, we come up with the fact that one foot pound of torque at 5252 rpm is equal to 33,000 foot pounds per minute of work, and is the equivalent of one horsepower. If we only move that weight at the rate of 2626 rpm, it's the equivalent of 1/2 horsepower (16,500 foot pounds per minute), and so on. Therefore, the following formula applies for calculating horsepower from a torque measurement:



Horsepower = Torque * RPM / 5252

Text

 

[Demon-Xanth]

Originally posted by: 91TTZ
Good post, pac.

That's why it annoys me when I hear a racerboy with no knowledge of engines say crap like, "yeah, the LS7 makes 500 hp but it needs 7 liters to do it! Hondas engines can rev to 9000 rpm!". Like you said, having to rev high is only a means to an end, it isn't the end, HP and a nice torque curve is.

Most people who use HP/L figures tend to ignore $/HP or actual engine weights.

Cheap
Powerful
Light

Pick two.

 

[91TTZ]

Originally posted by: JoLLyRoGer

Now, it's important to understand that nobody on the planet ever actually measures horsepower from a running engine. What we actually measure (on a dynomometer) is torque, expressed in foot pounds (in the U.S.), and then we *calculate* actual horsepower by converting the twisting force of torque into the work units of horsepower. [/L]

That is incorrect.

I had a long discussion about this on another forum, and emailed Dynojet Research to confirm it. A Dynojet directly measures horsepower, and back-calculates torque.

The reason lies in the way that dynos work. An inertial dynamometer knows the weight of the drum, the speed of the drum, and the time it took to accelerate it up to a certain speed. With that data, they can calculate the amount of *power* transferred to the drum during the run. With the tach connection, they get the RPM data, and with that they can back-calculate the torque.

If you've ever had your car dyno'd and the tach pickup isn't working right, the dyno will still know the horsepower produced, but it will not know the torque, since the element of rpm isn't known. But since the dyno directly measures horsepower, it will still give you your HP output.

 

[JoLLyRoGer]

Originally posted by: 91TTZ

Originally posted by: JoLLyRoGer

Now, it's important to understand that nobody on the planet ever actually measures horsepower from a running engine. What we actually measure (on a dynomometer) is torque, expressed in foot pounds (in the U.S.), and then we *calculate* actual horsepower by converting the twisting force of torque into the work units of horsepower. [/L]

That is incorrect.

I had a long discussion about this on another forum, and emailed Dynojet Research to confirm it. A Dynojet directly measures horsepower, and back-calculates torque.

The reason lies in the way that dynos work. An inertial dynamometer knows the weight of the drum, and the time it took to accelerate it up to a certain speed. With that data, they can calculate the amount of *power* that the drum stored during the run. With the tach connection, they get the RPM data, and with that they can back-calculate the torque.

If you've ever had your car dyno'd and the tach pickup isn't working right, the dyno will still know the horsepower produced, but it will not know the torque, since the element of rpm isn't known. But since the dyno directly measures horsepower, it will still give you your HP output.

Interesting.. I suppose that makes sense if it's measuring in terms of weight (of the drum) and time (taken to accelerate it). Way to do your homework dude! :thumbsup::thumbsup:

 

[91TTZ]

No problem, I'm always glad to help.

 

[skace]

This is a repeat, I've seen this episode already.

 

[radioouman]

Originally posted by: Injury
So, in layman's terms, would you guys say that horsepower is a measurement of the force at which a car is propelled foward?

And if horsepower is a constant, then the scope of its power is directly related the weight it must push?

Does a car deliver the same horsepower no matter how far in a person pushes the gas pedal?

yeah yeah, I'm a bit of a car n00b, but cars are one of the things I'd love to know much much more about than what gran turismo can teach

Maybe you should take some engineering classes too

 

[TomKazansky]

Originally posted by: ElFenix
Again, it just depends on what application you want to put the engine to work in. But more torque is always desireable. If race cars like Nascar or F1 could build engines that has so much torque that they only needed to turn 4000 rpms to move the cars as fast as they needed to go, they would. But that is impossible, so they build/gear them to suit their particular needs, based on the limitations of their respective rules.

actually, f1 engines are limited to 3 litres with 10 cylinders. There isn't that much torque that could be produced by a 3 litre. The only reason why it moves quickly at even low revs is because of its light weight. The reason why they can accelerate so fast and have such stable power for cornering is because of the smooth torque curve, percise gearing, and the ear-breaking 18,000 rpm redline.

with even 250 ft/lbs of torque at 18,000 rpm, you can generate 856 bhp at the redline.

of course when your building a luxary car (such as the rolls royce), you would want to have a massive engine that produces a lot of torque at relatively low rpm, since most people wouldn't want to shift and rev as much just to "go fast" on those cars.

But always remember that the more displacement you have, the bigger your engine will be, and the heavier it will be.

 

[JulesMaximus]

It determines whether the driver is a wussy little school girl or not.

For example:

142hp=Wussy little school girl
300hp=Russell Crowe in Gladiator
500hp=Arnold Schwarzenegger as a cyborg killing machine from the future!

 

[91TTZ]

Originally posted by: infestedgh0st

Originally posted by: ElFenix
Again, it just depends on what application you want to put the engine to work in. But more torque is always desireable. If race cars like Nascar or F1 could build engines that has so much torque that they only needed to turn 4000 rpms to move the cars as fast as they needed to go, they would. But that is impossible, so they build/gear them to suit their particular needs, based on the limitations of their respective rules.

actually, f1 engines are limited to 3 litres with 10 cylinders. There isn't that much torque that could be produced by a 3 litre. The only reason why it moves quickly at even low revs is because of its light weight. The reason why they can accelerate so fast and have such stable power for cornering is because of the smooth torque curve, percise gearing, and the ear-breaking 18,000 rpm redline.

with even 250 ft/lbs of torque at 18,000 rpm, you can generate 856 bhp at the redline.

of course when your building a luxary car (such as the rolls royce), you would want to have a massive engine that produces a lot of torque at relatively low rpm, since most people wouldn't want to shift and rev as much just to "go fast" on those cars.

But always remember that the more displacement you have, the bigger your engine will be, and the heavier it will be.

You pretty much just said the same thing he just said.

 

[TomKazansky]

Originally posted by: 91TTZ

Originally posted by: infestedgh0st

Originally posted by: ElFenix
Again, it just depends on what application you want to put the engine to work in. But more torque is always desireable. If race cars like Nascar or F1 could build engines that has so much torque that they only needed to turn 4000 rpms to move the cars as fast as they needed to go, they would. But that is impossible, so they build/gear them to suit their particular needs, based on the limitations of their respective rules.

actually, f1 engines are limited to 3 litres with 10 cylinders. There isn't that much torque that could be produced by a 3 litre. The only reason why it moves quickly at even low revs is because of its light weight. The reason why they can accelerate so fast and have such stable power for cornering is because of the smooth torque curve, percise gearing, and the ear-breaking 18,000 rpm redline.

with even 250 ft/lbs of torque at 18,000 rpm, you can generate 856 bhp at the redline.

of course when your building a luxary car (such as the rolls royce), you would want to have a massive engine that produces a lot of torque at relatively low rpm, since most people wouldn't want to shift and rev as much just to "go fast" on those cars.

But always remember that the more displacement you have, the bigger your engine will be, and the heavier it will be.

You pretty much just said the same thing he just said.

read the last sentence. and what he said was also what i said earlier.

 

[JulesMaximus]

Originally posted by: infestedgh0st

Originally posted by: 91TTZ

Originally posted by: infestedgh0st

Originally posted by: ElFenix
Again, it just depends on what application you want to put the engine to work in. But more torque is always desireable. If race cars like Nascar or F1 could build engines that has so much torque that they only needed to turn 4000 rpms to move the cars as fast as they needed to go, they would. But that is impossible, so they build/gear them to suit their particular needs, based on the limitations of their respective rules.

actually, f1 engines are limited to 3 litres with 10 cylinders. There isn't that much torque that could be produced by a 3 litre. The only reason why it moves quickly at even low revs is because of its light weight. The reason why they can accelerate so fast and have such stable power for cornering is because of the smooth torque curve, percise gearing, and the ear-breaking 18,000 rpm redline.

with even 250 ft/lbs of torque at 18,000 rpm, you can generate 856 bhp at the redline.

of course when your building a luxary car (such as the rolls royce), you would want to have a massive engine that produces a lot of torque at relatively low rpm, since most people wouldn't want to shift and rev as much just to "go fast" on those cars.

But always remember that the more displacement you have, the bigger your engine will be, and the heavier it will be.

You pretty much just said the same thing he just said.

read the last sentence. and what he said was also what i said earlier.

Read this:

It determines whether the driver is a wussy little school girl or not.

For example:

142hp=Wussy little school girl
300hp=Russell Crowe in Gladiator
500hp=Arnold Schwarzenegger as a cyborg killing machine from the future!

 

[Zenmervolt]

Originally posted by: everman
Torque and aerodynamics are also important factors, not to mention hauling around sumo wrestlers which will also kill top speed and acceleration.

Actually, weight has very little effect on top speed. Aerodynamics are several orders of magnitude more important to overall top speed. Conversely, aerodynamics have little play in acceleration (up to about 85 mph) while weight plays a very large factor in acceleration.

ZV

 

[Fox5]

Originally posted by: QuitBanningMe
WTF car do you have that is 1500 ponds?

I have a "light" car and it is 2600 pounds.

Lol, wasn't sure of my car's weight so I just picked one, my car is actually 2600 pounds.

Horsepower is the amount of raw power output times the power of a single horse.

1HP = the power of 1 horse.
500HP = a lot of horses.

I doubt my car could pull even as much as 100 horses.

This is why a car with a torque curve that falls off quickly (IE: engine can't breathe well at higher RPM's) isn't as much fun to drive and isn't as fast as as car that does have the torque up high.

Sounds like my car....I can get some decent acceleration at low speeds, but it really starts to struggle as it breaks like 40 mph.

 

[TomKazansky]

if you're not gonna be technical, don't post useless hp definitions.

 

[ElFenix]

Originally posted by: IHateMyJob2004

Originally posted by: ElFenix
horsepower is nothing more than torque at a high rpm. it means you don't have to shift as much.

the manufacturers put emphasis on hp because power figures aren't changed by the lever action of a transmission, while torque, as a type of force, is. so, each time you change gears your torque at the wheels is changing, but your horsepower isn't. which is why you accelerate harder in first gear than any other.

You are a retarded. Sorry about name calling rules, but this most accurately descirbes this post.

seriously, you have no clue wtf you're talking about.

the reason F1 cars have 900 hp is because they have a flat 250ish ft/lbs of torque from a few thousand rpm to damn near redline. the torque is constant, the rate of acceleration through the powerband is constant, the high redline allows them to stay in gear longer which means they don't have to have a 0 force state (neutral) for as long and can reach a higher top speed. the torque is the real thing doing the work, hp@whatever rpm really just tells you how much torque there is and gives you an idea of how flat the torque curve is. ideally, your engine would have constant torque from 0 to infinite rpm, but that isn't possible. so you build one with a pretty flat torque curve, and figure out the gearing so that just as the torque curve goes down too far you shift back to the begining of the torque curve and traverse it all over again.

why do you think you accelerate harder in first than any other gear?

 

[Calin]

Originally posted by: Pacfanweb

Originally posted by: Injury
So, in layman's terms, would you guys say that horsepower is a measurement of the force at which a car is propelled foward?
No, HP is a measurement derived from torque, which is basically what you described.

And if horsepower is a constant, then the scope of its power is directly related the weight it must push?
No, the power is the same, the weight determines how quick/fast you can go with that amount of HP. So do other factors, like traction and aerodynamics. Most passenger cars would not be able, if they didn't have rev limiters, to reach max. rpm in high gear...the wind resistance would be too great for their engines to turn up in high gear.

Does a car deliver the same horsepower no matter how far in a person pushes the gas pedal?
No. Max HP is only obtained at WOT. (wide open throttle)

yeah yeah, I'm a bit of a car n00b, but cars are one of the things I'd love to know much much more about than what gran turismo can teach

Google is your friend.

Wide open throttle and a certain rpm (or a range of rpm)
Force equal mass multiplied by acceleration.
Now, power is work over time, or force multiplied by distance over time (or force multiplied by speed)
So, power is force multiplied by speed
Torque is force multiplied by that force's arm of action (in this case, you can say the torque is equal to the force at the wheels multiplied by the radius of the wheel).

The torque at the wheels is influenced by the gear ratio (engine torque is reduced/multiplied by the gear ratio)