41 replies to this topic

[DOHCPower]

This is known as TQ , correct?

I was under the assumption, TQ is the only thing an engine produces, and that Horsepower is just a calculation based off the RPM the TQ is being delivered at / 5252. You cant 'measure' HP, you can only calculate it. You can, however, measure TQ. HP is just a measure of the engines efficiency, correct? But its an inderict measurement...

[McGuire]

LOL boy have we been down this road. If you use the search function you can find some interesting (or maybe not) piefights on this general topic. This is more of a philosophical question than an engineering problem, but since I stayed at a Holiday Inn Express I am fully qualified to answer. Personally, I don't see how it can be claimed that horsepower isn't "real" because it can "only" be calculated. As I see it torque and power can both be handled as real physical properties. Both of these properties do things which can be witnessed and measured.

However, it is true that it is impossible for humans to experience power directly through their physical senses. Folks may believe it is hp that is pushing them back in the seat, but that is not really true. However, that does not mean that power is not real or does not truly exist. That is a different question. In philosophy that line of thought is loosely known as "pragmatism" and leads to some very amusing conclusions.

[Stian1979]

Originally posted by McGuire
Folks may believe it is hp that is pushing them back in the seat, but that is not really true.

Yes it is.
Torque is static and not dynamic

[NTSOS]

Each blue ball represents a seperate thought process as each individual mind tries to contemplate/cope with concepts such as hp vs torque or SI vs CI engine braking.



John

[J. Edlund]

Originally posted by Stian1979


Yes it is.
Torque is static and not dynamic

Torque can be both static and dynamic, however, if it's dynamic there's always power involved.

Any decent physics book will describe power as work per time unit (and/or energy per time unit), while torque will be descibed as force vectors around an axis. Torque has the same unit as work but they should not be confused. Torque can be used to to work though. Work is described as force multiplied with distance.

For example lifting 75 kg one meter (vertical) requires 9,80665*75*1 = 735,5 Nm of work. If this lift is done in one second this translates into 735,5 Watt (power), if the lift is done in half a second it translates into 1471 Watt.

Lifting 75 kg one meter per second is the metric definition on a horsepower, thus, 1 hp = 735,5 Watt.

Using power as the basis it's also possible to calculate the acceleration or top speed of a car, airplane or similar.

[imaginesix]

Originally posted by NTSOS
Each blue ball represents a seperate thought process as each individual mind tries to contemplate/cope with concepts such as hp vs torque or SI vs CI engine braking.



John

Man, that blue ball factory is totally unrealistic, that's not how they're made at all.

Please God, let this thread die quickly.

[Wolf]

However, horsepower seems to be much more convinient measure for performance. If I was to e.g. say that engine has 135 Nm torque (BTW, we've always had this practice to express work in Joules, and torque in Newton meters, even though they're basically the same unit), would you be able to tell how fast the car goes (assuming you know drag, &c)?

The way I see it, engine produces energy (one would say, transforms chemical energy stored in fuel into mechanical/kinetic energy), while power describes the rate at which this happening.

[J. Edlund]

Originally posted by Wolf
However, horsepower seems to be much more convinient measure for performance. If I was to e.g. say that engine has 135 Nm torque (BTW, we've always had this practice to express work in Joules, and torque in Newton meters, even though they're basically the same unit), would you be able to tell how fast the car goes (assuming you know drag, &c)?

No, it's not possible to calculate the performance of a car (acceleration & top speed) from torque.

[hydra]

Originally posted by imaginesix

Please God, let this thread die quickly.

Amen...

[McGuire]

Originally posted by Stian1979


Yes it is.
Torque is static and not dynamic

Sure, and The Principle of Moments is a Robert Plant album.

[McGuire]

Originally posted by imaginesix
Man, that blue ball factory is totally unrealistic, that's not how they're made at all.

Please God, let this thread die quickly.

My favorite part is the two guys down at the extreme lower right. I think I worked at that place.

[Canuck]

Originally posted by McGuire


My favorite part is the two guys down at the extreme lower right. I think I worked at that place.

Why am I not surprised it's the shipping department. Looks like they've passed the UPS package handling course.

[McGuire]

I want to know how John got hold of such a highly confidential document. Only a few people are granted access to the General Motors organizational flow chart & business plan, and there are serious penalties for industrial espionage of this nature.

[imaginesix]

I just realised that the image can be tiled so that the blue balls cycle through an endless loop, none are ever lost or gained to the ether.
It's good to know that no blue balls were injured in the making of this movie.

[DOHCPower]

I have a different view regarding 'blue balls'.

[Greg Locock]

I work in the bottom right hand corner.

[Fat Boy]

Originally posted by McGuire
I want to know how John got hold of such a highly confidential document. Only a few people are granted access to the General Motors organizational flow chart & business plan, and there are serious penalties for industrial espionage of this nature.

He has a buddy that works at an airport. Kerkorkian's plane came through and that's what was sitting next to his Glenfiddich.

[Stoatspeed]

Originally posted by imaginesix
I just realised that the image can be tiled so that the blue balls cycle through an endless loop, none are ever lost or gained to the ether.

Sounds like a good cue for a discussion/argument on matters relating to Constant Entropy to me ... anyone up for the challenge??

[gbaker]

Don't you guys know a perpetual motion machine when you see one?

Got one right here. See, ya have the electric motor drive the generator, and the generator output is wired back to the electric motor. Poof, viola!

[Fat Boy]

Back to the topic on this one. MacG and I (among others)have been back and forth and we have basically came to the conclusion that he spelled out earlier.

Not to speak for him, but I think he prefers to look at things from the torque side because it can be used to calculate an acceleration of the car at any point in time.

I prefer to use HP because it allows me to more easily(in my head) determine acceleration over a given interval.

At the end of the day, they are interchangable (if using the correct equations for each value) and should be viewed as such.

[LS 1]

Originally posted by McGuire
LOL boy have we been down this road. If you use the search function you can find some interesting (or maybe not) piefights on this general topic. This is more of a philosophical question than an engineering problem, but since I stayed at a Holiday Inn Express I am fully qualified to answer. Personally, I don't see how it can be claimed that horsepower isn't "real" because it can "only" be calculated. As I see it torque and power can both be handled as real physical properties. Both of these properties do things which can be witnessed and measured.

However, it is true that it is impossible for humans to experience power directly through their physical senses. Folks may believe it is hp that is pushing them back in the seat, but that is not really true. However, that does not mean that power is not real or does not truly exist. That is a different question. In philosophy that line of thought is loosely known as "pragmatism" and leads to some very amusing conclusions.

Hmmmm. This brings to mind something that has been striking me lately, which is that it IS possible to physically experience the difference between hp and torque, so long as one is aware of speed-over-time.

Illustration:

I have a Dodge Cummings truck. 235hp, 440 ft.lbs. torque, 3.75 gears and a 5 speed. My wife has an older BMW 750. Oversquare V12, 340hp and 300 ft lbs. 3.73 gears. 4 speed auto.

I floor the Dodge at 5mph in 1st. The IMMEDIATE sensation is the kick-in-the-back of acceleration. But strangely enough after a few seconds the speedometer has not moved that much, I haven't traveled that far, and I have no particular sensation of gathering speed. Translation: Plenty of torque; not much HP, all physically experienced by the sensation of "acceleration not accompanied by speed at time progresses."

On the same piece or road I floor the BMW. The immediate, kick-in-the-back sensation is no more dramatic than with the Dodge, actually a bit less so. But when the car is passing 90 at about the time the Dodge is trying to reach 55, there certainly is a physical sensation which can be associated with the presence of "more HP but not as much torque."

[Stoatspeed]

Oh dear .... this one of those "apples and oranges" comparisons ...... or more like "apples and donkeys' for all the common factors which are at play ...

vehicle weight, driveline inertia, engine inertia, torque convertor performance, internal transmission ratios, aerodnamic drag, "perceived" performance factors (noise, vehicle attitude change ...) ...... all very significant aspects in drawing any conclusions here, and I'm not up for it ...
have at it, guys!

[LS 1]

Oh my.

Somehow my post has been read as saying the only difference between a Dodge pickup and a BMW 750 is the ratio of hp-to-torque? Or that an admittedly anecdotal experience, cited for illustrative purposes, is some kind of lab experiment in which all variables are accounted for?

No, I was only trying to illustrate a manner in which horsepower can be physically perceived as distinct from torque. Since the topic is perception, this is not a repeat of that wacky thread in which someone "proved" diesels have more engine braking because he could "feel it." Rather, the question is: Is horsepower something that can be felt? I'm just trying to suggest it can be, because we can perceive time and power over time is what HP measures.

[Gonzo]

LS 1, HP doesn't measure power over time, HP measures power. Power is work over time.

The physical entity perceived when accelerating your Dodge or BMW is force.

[J. Edlund]

Originally posted by LS 1
Oh my.

Somehow my post has been read as saying the only difference between a Dodge pickup and a BMW 750 is the ratio of hp-to-torque? Or that an admittedly anecdotal experience, cited for illustrative purposes, is some kind of lab experiment in which all variables are accounted for?

No, I was only trying to illustrate a manner in which horsepower can be physically perceived as distinct from torque. Since the topic is perception, this is not a repeat of that wacky thread in which someone "proved" diesels have more engine braking because he could "feel it." Rather, the question is: Is horsepower something that can be felt? I'm just trying to suggest it can be, because we can perceive time and power over time is what HP measures.

Power can be measured in many different units, horsepower (hp) and watts are the most common units. Before the first good steam machines horses was used in for example mining (water pumping, lifting etc), so when Watt offered his steam machine, miners had to know how many horses the machine could replace. So Watt studied how much power a horse could supply and used this as a unit of power - horsepower.

As for your acceleration test; your ass isn't a good accelerometer. Use a real accelerometer or at least a stop watch, then you can draw some real conclusions about power and acceleration. For a given car (mass and drag) the car with the highest average power output will always accelerate fastest.

As for the sensation, that is not so much related to power and torque as it is to other things.

[Greg Locock]

That's a good point. One of your more sensitive sensors is the tension in your neck muscles required to hold your head straight. Well, no it isn't. The thing you sense is the CHANGE in tension. That change in tension is proportional to the change in acceleration, which officially is known as 'jerk'. So, when your head feels like it is getting thrown about it is complaining about the change in acceleration, it tells you very little about the steady state acceleration.

Now, just to confuse things even more, your head has a certain resonant frequency in which it 'nods', on the stiffness of the muscles and tendons in your neck. So when you subjectively rate 'acceleration feel' a large part of your impression is due to the rate of change of acceleration of a single degree of freedom - which is a very long way indeed from what you are trying to measure.

That being said. the pressure in your back from the seat is a good indicator, but you have hardly any nerve endings there, and sigals from your back are desensitised to continual acceleration, otherwise you'd find lying on your back rather odd.

[Canuck]

Just when you think this place has gone the way of Chinese invaders and neighbourhood watch-do-gooders, a truly interesting post comes along. Thanks Greg.

[phantom II]

Two exercises you can do perform at home: I assume that you are sitting down right now with your feet flat on the floor. Apply the slightest pressure to one foot onto the floor. There is a corresponding pressure increase to the opposite cheek on the chair. It is here that you can feel if your airplane is in a slip.

There are many sensors down your spine which can sense the slightest mis alignment. This in conjunction with a myriad of other sensors, the inner ear and visual reference, instant auto-reaction decisions are made.
One of the most sensitive instruments is the inner ear itself http://oto.wustl.edu...hlea/intro1.htm
There are 3 semi circular tubes with millions of tiny hairs in the inner surface.The tubes are filled with a fluid of which any movement of the fluid will deflect the hairs. The position of the tubes, inner diameter, circumference of tube, fluid volume, viscosity, density, amount of hairs and their tension and thickness will vary from person to person. Another sensory input is pressure variation in motion detection. Blind people become more aware just how valuable all these internal instruments are. Fighter pilots have superior inner ears to most others.

To illustrate how important visual reference is for the correct interpretation of motion is, try this:

Position a rotating bar stool or office chair in a room with no audio or visual reference. (Blindfold). Feet should not come into contact with non rotating parts. Ask your wife or friend to begin rotating the chair one way, say to the left.

Which way are you turning?
To the left.

Wife/friend continues walking the chair to the left at constant RPM.

Which way are you turning?
To the left.

Which way are you turning?
slowing down.

Wife/friend still walking at constant speed.

Which way are you turning?
I'm am stopping.

Wife keeps walking.

Which way are you turning?
Stopped.

Wife slows pace but rotates in the same direction.

Which way are you turning?
To the right.
which way are you turning?
To the right.

Wife stops.

Which way are you turning?
Faster to the right.

Remove blindfold. Your eyes will rapidly move left to right and literally vibrate in their sockets. You will feel really weird.

Unusual attitude recovery with instruments in an airplane requires that the pilot is hooded during violent 3 axis movements. After removal of the hood, a complete recovery to horizontal flight must be made by instrument reference alone even though the student has max vertigo.
In other words, you can't count on what your body is telling you.

Originally posted by Greg Locock
That's a good point. One of your more sensitive sensors is the tension in your neck muscles required to hold your head straight. Well, no it isn't. The thing you sense is the CHANGE in tension. That change in tension is proportional to the change in acceleration, which officially is known as 'jerk'. So, when your head feels like it is getting thrown about it is complaining about the change in acceleration, it tells you very little about the steady state acceleration.

Now, just to confuse things even more, your head has a certain resonant frequency in which it 'nods', on the stiffness of the muscles and tendons in your neck. So when you subjectively rate 'acceleration feel' a large part of your impression is due to the rate of change of acceleration of a single degree of freedom - which is a very long way indeed from what you are trying to measure.

That being said. the pressure in your back from the seat is a good indicator, but you have hardly any nerve endings there, and sigals from your back are desensitised to continual acceleration, otherwise you'd find lying on your back rather odd.

[Greg Locock]

Here's some mor eof my random findings

Driver feedback is via

balance (semicircular canals)

muscle tension

steering wheel torque
steering wheel angle

visual

Seat/back/harness pressure on the body


One thing I get involved with is - which is the fastest? What is the upper frequency limit of each? Which do drivers actually trust when they are contradictory?

I don't know the answers, but, here's what I've found so far

You can drive fairly fast around a circuit using visual cues alone, but you'll fall of the road.

Vision is quite slow - 2 updates per second or so (this surprised me)

steering wheel inputs that are effective have an upper frequency limit of 3 Hz or so (this surprised me)

You don't need SWT to drive a car - 100% PAS is still drivable

SWT is very useful for sensing whether the front wheels are saturating.

Well, that's as far as i've got.

Incidentally they use these tricks with the 6 axis flight simulator rigs - the simplest example being tipping you on your back to simulate acceleration, i guess.

[gbaker]

Originally posted by Canuck
Just when you think this place has gone the way of Chinese invaders and neighbourhood watch-do-gooders, a truly interesting post comes along. Thanks Greg.

I concur. I wonder if Greg would like to compare and contrast these resultant Head G plots?


,

and

[desmo]

While too lengthy for me to type up here, there's some excellent insights about the human sensory variables and their limitations for car control in Peter Wright's F1 Technology book. Chapter 4, The Chassis and its Dynamics.

[Paul Ranson]

Vision is quite slow - 2 updates per second or so (this surprised me)

Can you enlarge?

It would seem at first thought that the central part of vision goes a bit quicker, I'm watching peoples lips on TV at the moment, normal word rates are 2-3 per second. Am I imagining what's happening inbetween?

Paul

[McGuire]

Originally posted by Greg Locock



One thing I get involved with is - which is the fastest? What is the upper frequency limit of each? Which do drivers actually trust when they are contradictory?

That is a very interesting question because a huge part of setup is getting a car that talks to the driver the way he wants it to.

[Greg Locock]

re the 2 Hz thing. I think that may be the time to build a full map of the visual field. Your brain actually makes up a lot of stuff to fill in the gaps. It is obvious from watching low quality video that 10 Hz is too slow for a small area that you are concentrating on. John Miles claimed that one reason why active cars set to zero roll were easier to drive fast was that your brain didn't waste time compensating for roll. I can't remember exactly if he was talking about visual or balance sensations for that, but I think he was talking about visual.

While we're at it another number from another study is that the processing speed of your vision system is around 5000 bytes per second. My background is noise and vibration - the human hearing system has a performance that is quite astonishing in some respects, given the amount of processing power available. For instance, when you tune a guitar by listening to the beats, you make decisions based on information that is too small to make a mathematical decision on- I think I know how, but it is still an amazing feat. I suspect that your vision system is much the same, synthesising rapid solutions for important stuff. Keeping a biped on its feet is a high priority, so establishing a horizon, and judging angular acceleration, are two things we are hard wired to do well.

I also remember talking to Richard Hurdwell, who was the prime mover behind the Lotus SID car, and his insistence that we fit a proper harness. He said that he hated wearing a harness when he
first had to, but since it knocked 2 seconds a lap off, he changed his mind very rapidly! I don't know what circuit or car that was, and it has the sound of made-up statistics to it. There again he is a very straight guy. Hmm, he works for the evil empire as well these days, I should quiz him a bit. I bet he's got a zillion theories on this stuff.

Gregg, I'll take plot number one thanks. It looks like you've got a mechanical problem on plot 2.

Do you have any data with a longer time scale? it looks like there is a 50 Hz resonance there on both plots, but that's only based on two cycles.

[shaun979]

SWT is steering wheel torque? What is PAS?

[Paul Ranson]

'Power Assisted Steering'

One thing we were discussing at the top of a hill somewhere was leaning the head/body into corners. The thought was that this makes it harder work because of the extra horizon compensation, but some drivers just can't help themselves.

Paul

[gbaker]

Originally posted by Greg Locock
...Gregg, I'll take plot number one thanks. It looks like you've got a mechanical problem on plot 2.

To say the least.

Do you have any data with a longer time scale? it looks like there is a 50 Hz resonance there on both plots, but that's only based on two cycles.

On other sleds going out to about 200ms you see the same general pattern, though severly damped. (The data acquisition shuts down on that sled at the 120ms mark.) This is probably a result of the harmonics you mentioned which, I suspect, is at a much higher frequency in the dummy than in the human. It wreaks havoc with the flexion/extension moments also, but that's another story.

What I find fascinating about the brain jerk is its relationship to shear, which has been correlated with injury via MR scans. We need to buff up our rheology before we can close that loop, though.

[dead_eye]

out of interest is there a rule for minimum torqe values for a given weight?

I.e (and i know im not using scientific terms but its been a long day lol) in theory a big torque engine say 1000lbft with a redline of say 100 rpm would pull a 1000lb weight 100ft a min. However if you took a small say 1lbft engine in theory if you revved it high enough it would pull the weight (its doing very little work but doing it very quickly).
However in reality untill you decrease the friction massivley a remote control car will never pull a 1000kg no matter how high you rev it (or will it if traction wasnt a problem??) as far as i can see if every part in the engine was unbreakable youd simply stall the engine?

And now im wondering if theres an upper torque limit after which the only way to increase acceleration is to increase bhp or at least the difference gained by adding more torque is negligable?

im wondering this because i was watching some old drag racing videos this week and one shows a rwd skyline repeatedly getting slain by a camaro running. Both are withing 50kg of each others weight, same tyres makes and looks like same size (very limited line slip makes it near ignorable anyway) and both running 700bhp. however the camaro was redlining at 7300 rpm while the skyline topped off at just over 9000rpm.

so the skyline has to have been making less torque and using the extra rpm to make up the same bhp figure.
But if the work done figure is the same then surely they should both finish at the same time? as 1 has more torque but is working slowly and the other has less torque but is working quicker??


I remember seeing a calculation showing a car with 500lbft and 100bhp would accellerate slower than an identical car with 100lbft and 500 bhp?? (i think the exact example was a diesel truck engine vs an f1 car.

ohh dear it was all so clear before i opened a few beers! ideas comments or facts please people before i have a confusion fit

[imaginesix]

No rule.

There have been too many threads like this to warrant a full reply, but you are a new member so don't feel bad. You can use the "Search BB" function to look up previous bickering, screaming threads about the relationships between hp, torque and performance.

The bottom line is that driven-wheel torque is what moves the car, and any power source can be geared down enough to acheive that desirded torque. Of course, the more you gear down, the slower you go.

[imaginesix]

OH, and welcome!

[dead_eye]

cheers bud, onto the search engine now lol

[J. Edlund]

Originally posted by dead_eye
out of interest is there a rule for minimum torqe values for a given weight?

I.e (and i know im not using scientific terms but its been a long day lol) in theory a big torque engine say 1000lbft with a redline of say 100 rpm would pull a 1000lb weight 100ft a min. However if you took a small say 1lbft engine in theory if you revved it high enough it would pull the weight (its doing very little work but doing it very quickly).
However in reality untill you decrease the friction massivley a remote control car will never pull a 1000kg no matter how high you rev it (or will it if traction wasnt a problem??) as far as i can see if every part in the engine was unbreakable youd simply stall the engine?

And now im wondering if theres an upper torque limit after which the only way to increase acceleration is to increase bhp or at least the difference gained by adding more torque is negligable?

im wondering this because i was watching some old drag racing videos this week and one shows a rwd skyline repeatedly getting slain by a camaro running. Both are withing 50kg of each others weight, same tyres makes and looks like same size (very limited line slip makes it near ignorable anyway) and both running 700bhp. however the camaro was redlining at 7300 rpm while the skyline topped off at just over 9000rpm.

so the skyline has to have been making less torque and using the extra rpm to make up the same bhp figure.
But if the work done figure is the same then surely they should both finish at the same time? as 1 has more torque but is working slowly and the other has less torque but is working quicker??


I remember seeing a calculation showing a car with 500lbft and 100bhp would accellerate slower than an identical car with 100lbft and 500 bhp?? (i think the exact example was a diesel truck engine vs an f1 car.

ohh dear it was all so clear before i opened a few beers! ideas comments or facts please people before i have a confusion fit

An engine in a remote controlled car can produce up to 2-3 hp and it will produce work per time unit equal to that 2-3 hp. That it works using high revs and low torque does'nt change that fact, and it will be capable of the same performance as any other any other engine with this output, given the correct gearing of course.

In reality, the low weight of a radio controlled car, and the incorrect gearing would not allow the car to pull a weight of 1000 kg against a flat surface. Even if the friction against the surface was very low that would be unrealistic.

If two cars that seems equal shows a difference in performance that isn't related to torque output if the engines provides the same power output. But it's important to note that for acceleration, it's the mean power output that does the trick, not the peak power output. Also, another important factor is how much of this power that actually can be used. For example a motorcycle often has more power in relation to the weight compared to a car but on a track the car might out accelerate the motorcycle on certain parts of the track. That is not relateed to the lower torque output of the motorcycle but the limited traction availible. If we compare time at full throttle for a lap around the track, the car will ne able to run with full throttle for a longer period of time hence increasing the mean power output of the engine.