n00b question
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From: Lastweek Lane - Watertown, NY
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n00b question
I believe I understand what torque is and what horsepower is, but if they're interrelated (should cross at 5200rpm), then what's the significance of the difference between the two?
With regards to the S2000, it has a much lower tq rating vs hourspower, whereas the STI is even/even.
When I get home to the states shortly, and get my first opportunity to tune my car on a dynometer, what would the significance be if I were to see, say a tq number that 30 less than the hp number...or 80 less...or 20 more? Is there an interrelation as far as that goes?
Thanks
With regards to the S2000, it has a much lower tq rating vs hourspower, whereas the STI is even/even.
When I get home to the states shortly, and get my first opportunity to tune my car on a dynometer, what would the significance be if I were to see, say a tq number that 30 less than the hp number...or 80 less...or 20 more? Is there an interrelation as far as that goes?
Thanks
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Well, I'll take a crack at this, just to be polite, and I'll be interested to see what other responses (agreeing or not) emerge.
"Horsepower sells cars, but torque wins races" (I wish I knew the source.)
Power (horse or other) is the rate of energy production an engine can manage.
Energy is force through a distance (so that, for example, it takes force to hold up a weight against gravity but energy to lift it).
Torque is the (twisting) force generated by the engine.
In general, torque/power curves in engines are a product of the specific design. I think it's fair to say that your attempts to create relationships between the two are pretty artificial. It may be that, for a particular engine, the relationships for stock vs. modified will change depending on the mods, but comparing different engines' relationships is not especially meaningful. HPH
"Horsepower sells cars, but torque wins races" (I wish I knew the source.)
Power (horse or other) is the rate of energy production an engine can manage.
Energy is force through a distance (so that, for example, it takes force to hold up a weight against gravity but energy to lift it).
Torque is the (twisting) force generated by the engine.
In general, torque/power curves in engines are a product of the specific design. I think it's fair to say that your attempts to create relationships between the two are pretty artificial. It may be that, for a particular engine, the relationships for stock vs. modified will change depending on the mods, but comparing different engines' relationships is not especially meaningful. HPH
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Originally Posted by gpatmac
I believe I understand what torque is and what horsepower is, but if they're interrelated (should cross at 5200rpm), then what's the significance of the difference between the two?
With regards to the S2000, it has a much lower tq rating vs hourspower, whereas the STI is even/even.
When I get home to the states shortly, and get my first opportunity to tune my car on a dynometer, what would the significance be if I were to see, say a tq number that 30 less than the hp number...or 80 less...or 20 more? Is there an interrelation as far as that goes?
Thanks
With regards to the S2000, it has a much lower tq rating vs hourspower, whereas the STI is even/even.
When I get home to the states shortly, and get my first opportunity to tune my car on a dynometer, what would the significance be if I were to see, say a tq number that 30 less than the hp number...or 80 less...or 20 more? Is there an interrelation as far as that goes?
Thanks
Also, torque is a measure of force, while horsepower is a measure of work. That's the simple explanation of why they are different when measured. Check these short papers on racing phsyics for a little more help.
Originally Posted by HPH
Energy is force through a distance (so that, for example, it takes force to hold up a weight against gravity but energy to lift it).
Actually force times distance = work, which is a change in energy (not the same thing as 'energy').
The problem is that you are using a potential energy equation to explain a kinetic process. Potential processes are chemical, gravitational (as in your example), elastic, etc....
Energy is the capacity to do work.
Yes, the units are the same..and it's easy to get confused.
Torque is a measure of work. The force needs to be perpendicular to the distance.
It's measured in Newton*meters (Nm) or joules
Horsepower is a *rate* and is measured in work/second such as joules/sec, ft lb/sec etc....
A horsepower is equal to 550 ft lb/s.
Hope this was helpful and not too confusing.
Actually as I re-read my post it may be too much info...so hows this:
Torque spins the wheels, gives you that 'neck snap' upon acceleration.
Horespower is how fast you can do it.
For example, you may have a race between a body builder and a sprinter. Sure the body builder can do more work, but he can't do it fast enough to compete.
Torque spins the wheels, gives you that 'neck snap' upon acceleration.
Horespower is how fast you can do it.
For example, you may have a race between a body builder and a sprinter. Sure the body builder can do more work, but he can't do it fast enough to compete.
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Another thing I hope someone comments on is that I read last night, shortly after posting, that torque is a constant, which initially didn't make sense to me until I remembered that it is normally a coefficient to rpm.
It also becomes clearer to me when I thought about it from the perspective of the above analogy, weightlifter vs. sprinter. Or maybe even better, between a distance runner vs. a sprinter (fast twitch muscle fiber vs. slow twitch (I'm sure I'm bastardizing my analogy
).
Lastly, WRT what HPH says, "In general, torque/power curves in engines are a product of the specific design. I think it's fair to say that your attempts to create relationships between the two are pretty artificial. It may be that, for a particular engine, the relationships for stock vs. modified will change depending on the mods, but comparing different engines' relationships is not especially meaningful. HPH"
This is entirely why I'm asking my question. The stock WRX engine has a more or less static ability to produce power (notwithstanding the Wednesday car factor). However, everytime something is added or reduced from the car (ie. power builder or weight reduction), it affects power at the wheels.
I have replaced the 207 block with a 257, the TD04 with a green, the TMIC with a FMIC, exmanifold with headers, entire exhaust system with larger, less restricted piping. Also, just the simple act of adjusting boost can be a major factor.
I've been tuning with the UTEC/TUNA for quite a while now and in the near future, I'm going to have my first opportunity to tune the car on a dyno as opposed to on the highways and backroads of Oahu. I asked myself what it was I was shooting for and realized that essentially I didn't have that clear of an idea. 'I want more power, yo'. That seemed a little too short-sighted and ignorant, so I started thinking about what questions were appropriate to start searching for answers on.
I figured that I wanted lots of torque, right now. From that, the penultimate question seemed to be how much torque and should I worry about horsepower.
From that came, I wonder if there is a certain ratio that should be targeted.
Most likely I'm chasing my tail, but my experience shows me that that technique has been where I've learned the most. I am unable to fully grasp the concept and so I'm trying to validate or throw away the assumptions I have.
It also becomes clearer to me when I thought about it from the perspective of the above analogy, weightlifter vs. sprinter. Or maybe even better, between a distance runner vs. a sprinter (fast twitch muscle fiber vs. slow twitch (I'm sure I'm bastardizing my analogy
).Lastly, WRT what HPH says, "In general, torque/power curves in engines are a product of the specific design. I think it's fair to say that your attempts to create relationships between the two are pretty artificial. It may be that, for a particular engine, the relationships for stock vs. modified will change depending on the mods, but comparing different engines' relationships is not especially meaningful. HPH"
This is entirely why I'm asking my question. The stock WRX engine has a more or less static ability to produce power (notwithstanding the Wednesday car factor). However, everytime something is added or reduced from the car (ie. power builder or weight reduction), it affects power at the wheels.
I have replaced the 207 block with a 257, the TD04 with a green, the TMIC with a FMIC, exmanifold with headers, entire exhaust system with larger, less restricted piping. Also, just the simple act of adjusting boost can be a major factor.
I've been tuning with the UTEC/TUNA for quite a while now and in the near future, I'm going to have my first opportunity to tune the car on a dyno as opposed to on the highways and backroads of Oahu. I asked myself what it was I was shooting for and realized that essentially I didn't have that clear of an idea. 'I want more power, yo'. That seemed a little too short-sighted and ignorant, so I started thinking about what questions were appropriate to start searching for answers on.
I figured that I wanted lots of torque, right now. From that, the penultimate question seemed to be how much torque and should I worry about horsepower.
From that came, I wonder if there is a certain ratio that should be targeted.
Most likely I'm chasing my tail, but my experience shows me that that technique has been where I've learned the most. I am unable to fully grasp the concept and so I'm trying to validate or throw away the assumptions I have.
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Originally Posted by syncopation
Yes, the units are the same..and it's easy to get confused.
Torque is a measure of work...
Torque is a measure of work...
But otherwise you're falling victim to your own confusion. Just because torque has units of work doesn't mean it is. The torque has to be applied through an angular distance before any work is done.
Just like holding a weight against gravity requires force while lifting it (through a distance) is work, pushing hard on, say, a lug wrench is exerting torque, but unless the thing moves, you haven't really done work, in the sense of this discussion. And it's how fast you make it move that represents the power. HPH
Originally Posted by HPH
.... The torque has to be applied through an angular distance before any work is done.
Torque is a measure of work, not work, because it is a vector (which implies of course that work is scaler).
I was simplifying 'angular distance' into a perpendicular cross product, sorry.
It's funny how often this discussion comes up!
gpatmac- Here is a great article that may give you some insight into your problem:
http://www.westechperformance.com/pa...ng/hpvstq.html
Great stuff!!!
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Thanks muchos, everyone. Certainly helped to put things into perspective.
Thanks a bunch, syncopation and BAN.
Now I've got something to keep me occupied here in the CJOC. (It's a slow night in the Combined Joint Operations Center)
Thanks a bunch, syncopation and BAN.
Now I've got something to keep me occupied here in the CJOC.
(It's a slow night in the Combined Joint Operations Center)
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synco,
I know I'm slow, but that has got to be one of the most direct and informative automotive article I've read yet.
Ban, I'm going to look at some from the page you posted, tomorrow.
Thanks
I know I'm slow, but that has got to be one of the most direct and informative automotive article I've read yet.
Ban, I'm going to look at some from the page you posted, tomorrow.
Thanks
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i'm out of my league here...
but one of my buddies explained to me in lamans
terms the relation between the 2.
the way he put it... very simply of course is this-
"torque will get you there, and your horsepower will keep you there"
i know thats not very scientific but it made sense to me at the time.
*<hijack-sort of>and while i'm here... can someone clearly explain to me about ps -
i notice in japan they use that rating instead of h.p.- and what relation it has directly to torque?
aloha from the summit of Mauna Kea
but one of my buddies explained to me in lamans
terms the relation between the 2.
the way he put it... very simply of course is this-
"torque will get you there, and your horsepower will keep you there"
i know thats not very scientific but it made sense to me at the time.
*<hijack-sort of>and while i'm here... can someone clearly explain to me about ps -
i notice in japan they use that rating instead of h.p.- and what relation it has directly to torque?
aloha from the summit of Mauna Kea
Originally Posted by gdogg
<hijack-sort of>and while i'm here... can someone clearly explain to me about ps -
i notice in japan they use that rating instead of h.p.- and what relation it has directly to torque?
i notice in japan they use that rating instead of h.p.- and what relation it has directly to torque?
Europeans didn't like our scale system so they devised an eerily similar system merely to confuse us auto enthusiasts (or maybe it was us Americans?).
A PS unit is measured in kilogram*meters/seconds and 1 PS=75 kgm/s. Really its just metric horsepower.
The PS is 98.6% of a bhp (brake horse power).
1 bhp = 1.013869 PS
As for why they use it in Japan, I don't know (I mean historically, besides the fact that it's metric). Anybody know what "horespower" is in Japanese?
The relation to torque is that it is a rate (same as bhp). Torque in this system should be listed as kilogram*meters (kgm). Magazines frequently get this wrong, stating PS in kgm/s, and then torque in Nm.
BTW...interestingly.. car companies almost always list bhp as PS because it is a slightly higher value. Good for marketing.
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I found this:
Helping [myself] to shed a little more light [for myself]
I'm starting to understand the relationship, I'm still finding it hard to apply it to engine building and tuning.
I'm still searching...
BTW: I just found a ps is equal to a metric hp (BHP, right? edit: no, doesn't look like it, although it looks like ps is equal to metric hp.)
227 hp = 230.148 ps
Suppose you want an engine that puts out 600 ft-lb of torque. Sounds pretty impressive, doesn't it? Well, let's see. Suppose we removed your engine, put a 3 foot breaker bar on the input shaft to your engine and I sat on it. Correctly assuming that I weight about 200 lbs, you would then have a force of 600 ft-lbs (3 feet x 200 lbs) applied to your drive train. However, that is all that 600 ft-lbs is - a static twisting force and it says nothing about whether you actually moved your car; or, more importantly, whether you moved your car quickly. If I sit on the breaker bar all day long without moving it, I've applied a lot of torque (force) for a long time, but I didn't move your car. So saying that 600 ft-lbs of torque is being applied to your transmission input shaft doesn't tell you anything about whether you've moved your car.
OK. Let's say I sat on the breaker bar and it actually moved; it rotated so that I was lowered toward the ground. Now we have done some work. We moved something. Work is defined as force times the distance through which it acts. Or more simply force times distance (f x d). We can view this as the force applied by the rear tire to the ground in accelerating the car multiplied times the distance the car moves. Let's say that I'm strong enough to turn the breaker bar one full revolution while applying 600 ft-lbs of torque (probably not that easy, even with a 3 foot breaker bar). Well, now we're moving the car; we're doing work. But how quickly do you think we'll cover the quarter mile with me turning the transmission input shaft? Maybe in a day or so? That's not impressive. So to this point, we've decided that defining the amount of torque applied to your drive train is not enough.
What we really want to do is to move the car and do it quickly. We want to accelerate a car through the quarter mile as quickly as possible. That is to say we want apply a force (engine torque applied through the tire to the ground) to move a car (with motion, the force becomes work) and move it quickly (travel a distance in a short amount of time). In short, we want to maximize the value [(force x distance)/time]. This happens to be the definition of power. We want to maximize power. We want to apply a force to your car (torque applied to the ground through the tire) and have that force actually MOVE the car (the force acting over a distance now can be called work) and we want to do it very quickly; in a short amount of time (work divided by time equals power).
OK. Let's say I sat on the breaker bar and it actually moved; it rotated so that I was lowered toward the ground. Now we have done some work. We moved something. Work is defined as force times the distance through which it acts. Or more simply force times distance (f x d). We can view this as the force applied by the rear tire to the ground in accelerating the car multiplied times the distance the car moves. Let's say that I'm strong enough to turn the breaker bar one full revolution while applying 600 ft-lbs of torque (probably not that easy, even with a 3 foot breaker bar). Well, now we're moving the car; we're doing work. But how quickly do you think we'll cover the quarter mile with me turning the transmission input shaft? Maybe in a day or so? That's not impressive. So to this point, we've decided that defining the amount of torque applied to your drive train is not enough.
What we really want to do is to move the car and do it quickly. We want to accelerate a car through the quarter mile as quickly as possible. That is to say we want apply a force (engine torque applied through the tire to the ground) to move a car (with motion, the force becomes work) and move it quickly (travel a distance in a short amount of time). In short, we want to maximize the value [(force x distance)/time]. This happens to be the definition of power. We want to maximize power. We want to apply a force to your car (torque applied to the ground through the tire) and have that force actually MOVE the car (the force acting over a distance now can be called work) and we want to do it very quickly; in a short amount of time (work divided by time equals power).
I'm starting to understand the relationship, I'm still finding it hard to apply it to engine building and tuning.
I'm still searching...
BTW: I just found a ps is equal to a metric hp (BHP, right? edit: no, doesn't look like it, although it looks like ps is equal to metric hp.)
227 hp = 230.148 ps
Last edited by gpatmac; Aug 10, 2004 at 01:43 PM.
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