Oh, but that is exactly what you are trying to do, dumb down the information, therefore making it easier for you to formulate a response, suited to *your* position and circumvent the limited facts that are mostly provided by your crystal ball.



BTW, who appointed you Oracle in charge of creating a pretend syllabus intended primarily "as a useful wake-up for those on this forum"?



You mean to tell me that all I have to do is agree with your shamefully silly exercise and I can become a man? Wow, that would be easy, but sorry......no thanks!



Sorry, I will never agree your definition of "importance"....the parameters that you are constantly trying to advocate are too painfully limiting even for a pretend exercise.....I will only allow myself to think in complete sentences..........or in this case, complete torque curves or as a last resort, P curves, if I must!

Anyway, I get a hoot in the way these 2 guy's view the real world of the IC engine.....I would substitute here and there and I have used bits and pieces but they pretty much get it.






Are you guys talking about the links located at the bottom of my pretend website? If so, those are linked to Nelson Racing and they work for me!

John

That looks like something from Bob B's site.

At the end of the day, it's pretty hard to say that any single parameter is the defining characteristic of an engine. No individual measure gives you complete picture.

And nobody here is claiming it does. Each measure however may be most appropriate for painting its particular part of the picture.

When comparing acceleration potential of two engines (V8 vsV10) with limited information - say the 5 presented by myself earlier - I would say all 5 are useful for comparing the engines (if you have them), although peak-power is the most important.

Further - if you can only pick ONE from the five, peak-power is THE ONLY ONE OF THE FIVE THAT IS ANY USE AT ALL, WHEN VIEWED IN ISOLATION.

Notice how carefully the author is skipping over the part about how that rpm band is determined, it's just thrown out there as if it is a given. Of course it isn't, that band is defined by the power curve, but saying that would kind of kill the point of glorifying torque. Therefore, great care is taken to obfuscate the explanation to make it sound like torque is the king.

Why not just cut to the chase and say that it's the spread of power around the power peak that matters? I've never figured out the reason for this. I guess some people are just too much in love with the word "torque" to think clearly, and would rather offer unnecessarily cluttered explanations.

I believe gruntguru, ranson, guller, have the more balanced view and been much clearer in what they're saying. The rest seems to be a lot of obfuscation, and quoting without understanding context.

The problem with regarding power as "more important" than torque: It is the engine's torque curve that defines its power curve and makes a useful power range possible.

The list of five items is a pointless exercise. All five combined are woefully insufficient in selecting a serious racing engine. Here is a superficial approach designed to produce a superficial conclusion. Meanwhile, max power is the most hyped and misrepresented figure in all of motorsports. For the most part it is safe to regard power figures as numbers of negative informational capability. Unless there is further information backing them up, they are almost certainly inaccurate if not outright fabrications.

I bet you wish you would have never posted that "clever" exercise.

In any case, it doesn't take balls, only common sense and I am simply not going to play down to your "excercise" in limited thinking....we don't agree, now go away!

John

Hi Canuck,

Would that be R B Racing?

Thanks!

John

The exercise is there to make people think - I don't really care if anybody posts their thoughts.

If it made you think - I am happy.

By your definition of limited thinking - this whole thread is an exercise in limited thinking and very worthwhile IMHO.

Much more frightening is "narrow" thinking - refusal to look at anything from more than one angle.

Indeed. One of my favourite ranters.

I don't think I said they were useless, only that it's akin to the blind men and the elephant. Everything is accurate and correct, but none of them (or even all of them together in this case,) provide a complete picture.

Having not gone down this particular rabbit hole before, I didn't know you could determine wheel thrust with hp alone. Even now however, I'm not entirely certain what thrust is a measure of. I'm unclear on why you can ignore the torque multiplication of the drive train and still come up with a useable measure. You might as well tell me you can calculate spirons (as opposed to thrust) or some other unitless confabulation - I wouldn't know any better.

At this point I'm not sure how you can derive acceleration potential from an instantaneous snap-shot number either. Going back to my own experience wherein I beat the ever living hell out of my poor motorcycle on the dyno in an effort to understand more, there were combinations of valvetrain, intake and exhaust that produced impressive peak hp, but were utterly horrific to ride and even when dragging could barely pull itself out of it's torque (or power if you will) dip to make it exciting. Conversely (of course), other combinations didn't produce nearly the peak power but were much easier to ride and accelerated much quicker in same-gear and through-the-gears scenarios. This is why I say that peak hp is misleading as a performance indicator.

I suppose if you put it in the right box, I.E. we assume that we know it's well tuned, we know it has a linear power (or torque) curve, we know the drivetrain is geared to match the engine's unknown operating speed, then yes I suppose peak HP is the most desirable measure...if you understand what the thrust unit is conveying (which I don't). Going one step further - within the bounds of this thread, we know almost nothing about the engines in question (though we can make some educated guesses based on sound ICE theory). The entire premise is a bit wishy-washy. If we can estimate, based on some educated assumptions and math, hp figures, we can do the same with rpm and tq, wherein we'll now "know" as much from a torque perspective as we do from a horsepower one.

I'm not suggesting one is greater or more important than the other - last thing I want is to get tangled up in that side of this thread. In all honesty I'm not sure what all the fuss is about.

Again, not wanting to get tangled up in this...and I'm asking in sincerity not provocation:

If a/f compressed and burned produces heat and linear motion, which is converted to rotational motion, it's fair to say that the ICE produces torque (and heat and exhaust and blah blah blah) is it not? Is it accurate to say that HP is a measure of how quickly that torque is produced? If those are both accurate statements, then it would seem that HP is akin to km/h and TQ to km. Well...if we have no km, there's no km/h - it's rather fundamental to the whole measure. So, if we have no torque, there's no HP. Which, again assuming I've not wandered off the path too far, suggests that HP must be derived from TQ. Doesn't it?

That would further suggest then that the RPM band is determined by the torque curve (not peak torque) and not the HP curve (because the HP curve is derived from the torque curve).

Or?

Thrust is the linear force (in lbs or N or whatever) acting at the tyre contact patch, that accelerates the vehicle. So if you have a 2000lb car and the thrust at the tyres is 1000 lb, it will be accelerating at 0.5g (neglecting aero drag etc). With 2000lb thrust it will accelerat at 1g and so on. This thrust is a resultant of rear-wheel torque acting at the contact patch.

0.5g is actually a very fast car if you are doing say 50 mph - that takes a lot of power. On the other hand, must manual trans RWD cars can achieve 0.5g with a clutch dump at 0 mph - that requires no power at all (no useful power at least - the tyre shredding absorbs a fair bit). Yet the rear wheel torque requirement is the same for both cases! So the power required increases with road speed according to Thrust x Speed = Power. Note we can work backwards to calculate how much Thrust is available at any speed. The only assumption when you do this is that you can select an approriate gear to place the engine at its peak-power rpm. If you have a CVT or an engine with a flat power peak, you will be able to achieve maximum thrust (and therefore maximum acceleration) at all road speeds.

Yes, it's true, but I also fail to see how it is not trivial. What exactly is the purpose of such an exercise in deconstruction, and how does it help us understand the dynamics involved?

It's true that torque provides one out of the two pieces that make up power, and obviously without any of the component pieces you won't have the whole thing. My question is, so what? I'm not being provocative either, I'm just trying to understand the point of that observation.

You can ignore torque multiplication because it is embedded in the power figure. When you drive at a certain speed and shift down into a lower gear, think about what happens. The obvious thing that happens is that you're choosing the gear with the higher torque multiplication. The less obvious, but actually equivalent effect, is that you increase your engine RPMs, and that is reflected in the power that your engine is putting out.

It can be proved mathematically that maximizing the product of torque and torque multiplication is equivalent to maximizing the product of torque and RPMs (or power, in other words). This is why we don't need torque multiplication when using the power method. It's a redundant piece of information when you know power.

The fact that power curve is derived from torque curve is another true, but trivial statement that is often repeated in these kinds of debates. It doesn't help us understand the dynamics involved, but it does help to confuse the issue. Just because power curve is fully derived from the torque curve doesn't mean that we should use just one of those.

Obviously anything that you can determine from the power curve you can determine in a more complicated way from the torque curve. However, doing that makes about as much sense as analyzing acceleration of a car by looking at its distance over time graph. Yes, you can actually do it, the acceleration graph of a car can be derived entirely from its distance graph, but why would you want to ridiculously complicated such a simple task?

There is a very good reason why we use derived units in science. They're there to make the description of complicated concepts cleaner. Some people here seem to have an attitude that your understanding of the fundamentals involved is inversely proportional to how highly derived the units you're working with are. That's just utter silliness.

I guess torque people are just trying to say that torque exists ,and can be measured,but power does not exist and is theoretically calculated by graphing torque over time,at various rpm if you like,to see how much work that certain engine with that amount of torque can be expected to do in the real world in the type of vehicle it will be placed. Getting dyno readings at a car show ? ---I really would find it more interesting to watch grass grow.

A steam engine develops maximum torque at zero rpm,but is not "at work".Pulling a train at 80km/h up a grade it is producing a huge amount of power from the torque which is available from moment to moment.As a fully laden steam train slows on a gradient,the torque available increases until loss of traction becomes the limiting factor.Hope this helps.

Actually power and torque both exist and can both be measured. Interestingly though, neither can be measured directly - even torque!

There are only seven fundamental units from which all others are derived and defined. They are:

Distance
Mass
Time
Electric current
Temperature
Amount of substance
Intensity of light

The traditional methods for measuring torque measure perpendicular force at a distance from the shaft axis. The force measurement itself is usually made by measuring deflection (displacement) of an elastic material. In the old days this would be a spring balance with a scale. These days it is usually a "load cell" which uses electrical resistance strain gauges to measure the deflection of a fairly stiff spring element.

Lets me propose then that torque exists as twisting force,and we are specifically interested in how much work that twisting force ,which finds its way to the driven wheels of a car, can do .Because it is going to take some period of time for work--accelerating to and maintaining top speed--to be achieved,torque is more fundamental than power.Power derives from torque.Power is the result of torque being applied through the torque band of the engine.Compromises are reached as to what rpm range is useable due to selected (eg racing,commuting,cruising) constraints ,and technological advancement.(can it rev at 10000rpm for hours?)

No matter how huge or fluid the torque of a practical-sized petrol engine, it is not going to drive you across 3 counties in 10 seconds.It has the torque to do the job but it also needs the time,no matter how hard it is revved.

Some info on units and derivations (dimensional analysis is quite a handy tool for sanity checks) :
http://en.wikipedia.org/wiki/Fundamental_unit
http://en.wikipedia.org/wiki/Dimensional_analysis

I think it is misleading and simplistic to think in terms of one unit being more fundamental than another. Power is the rate at which energy flows and comes in many forms - most of which have nothing to do with torque. In the case of heat engines (including Otto cycle piston engines), thermodynamicists think primarily in terms of power and work, since the engine in its most simplified definition is a device for converting heat energy into waste heat and work.

On the other hand torque is easily manipulated, via gearing for example. If we take the drive from the camshaft (which some engines do) we get double the torque, yet power (and BMEP) remain the same.

The concept of torque being somehow more fundamental than power stems from the technique used to measure power of engines ie dynamometer torque times engine speed. If all dynamometers lacked a torque sensor and we had to measure the heat generated in the brake to calculate the power then divide that by engine speed to get a torque number, people might have the opposite view (power is more fundamental than torque) although this would be incorrect also, since neither is more fundamental.

I think the reason for some people suggesting torque is fundamental comes from the physical gas expanding in the cylinder pushing on the piston, a force, turned into a torque by the connecting rod and crank bit of the crankshaft.

But this ignores time. Which ticks in a most fundamental way.

Paul

OK I see where the Power People are coming from.The FORCE (MAY IT BE WITH YOU) begins in the enclosed chamber,but although it can be calculated I guess,I can't see how it becomes measureable in an Automotive setting until the conrod,crank etc convert it to a spinning shaft which can be made to do work ,enabled by torque ,over time.It is controversial enough with dyno readings not "singing from the same song book" when they only have to measure torque,imagine the benchmarking problems if they attempted to measure heat to get an answer.What a leaky bucket.
Thus I rest my case Torque is fundamental to extracting measurements of Power anywhere beyond the development laboratory,for automotive applications.That is to say you cannot MEASURE Power , FIRST.

That's not the half of it. More importantly: while power is derived from torque, they are also two distinct properties. For example, the one you feel pushing you back in the seat is the resultant of torque, not power. This is easy to prove in case it is not totally obvious. Dimensional analysis indeed. When you push on the throttle pedal and say, "Wow, feel that power," everyone gets the gist of what you are talking about, but from a purely technical perspective that is incorrect. The actual property to which you are referring is torque.

While your heat-based dynamometer is correct in theory, in practice it could never be accurate as there are too many undefined and uncontrolled variables. Dynamic machines are relatively unstable and nonlinear in efficiency. That's why we need dynos in the first place. If it were that easy we could simply calculate power by measuring the fuel consumed.

In reference to your previous post: Of course torque can be directly measured, just as it can be physically experienced. You have measured it yourself if you have ever used a beam-type torque wrench to tighten a fastener. With an external combustion engine (steam, say) or a DC motor we could use this same method to measure torque at zero rpm. On an internal combustion engine with a revolving output shaft it's a little more complicated, but not much. We simply place a resistance unit (a water brake for example) on the shaft while the beam is placed between the resistance unit and the machine bed. Now we can measure the force while the shaft is rotating, and off we go. The measurement is entirely direct, valid, and accurate. Torque is a real property in the physical world.

On the other hand, I would not assert that power, an exclusively calculated property, does not "exist." That's a philosophical/ontological question, and at the bottom of it this question: Does mathematics exist in the world or in the mind? In the thousands of years people have been knocking that question around, no one has been able to prove that mathematics exists anywhere but in our minds -- no pi in the sky. Nor can it be disproven, for that matter. There is no valid test. In that regard it is identical to all arguments for/against the existence of a supreme being. Take your choice. Personally, I am a skeptical agnostic on the subject. For me it's enough to say that power exists as a valuable property in the understanding and operation of machines, among other matters, even though it can "only" be calculated.

Well, it's not totally obvious. In fact, it's plainly wrong unless car speed equals zero (then we have acceleration without power). When the speed of the car is greater than zero, the thing pushing is power!

I think what McGuire is saying is the amount of "push in the back" you feel is proportional to torque, although it is rear-wheel-torque not engine-torque.

Engine-torque and rear-wheel-torque only remain in proportion if there are no gear shifts and no variation in torque converter multiplication.

engine torque is at the crankshaft ,through other shafts and gears,does its work at the tyre contact patch.It can do one of 2 things,propel the car forward or spin the earth backwards.It will do neither during gearchanges,however.As far as rear wheel torque and engine torque remaining in proportion,that is kind of silly concept.Any manual,automatic,diff ratio or rear wheel diameter changes will affect the acceleration or pulling ability at the tyre contact patch due to torque leverage via the final gearing--it comes out in the wash and must be correct,minus losses.

Your car seems to have more power IN FIRST GEAR THAN TOP,but all thats happened is the engine torque is multiplied by gearing.

The point I am making is "push in the back" is not always proportional to engine torque because gear changes etc will also change the "push in the back" (also known as thrust).

On the other hand "push in the back" is always proportional to Power divided by vehicle speed - no matter what gear you are in.

Holy shit, I really can't believe this 'debate' is still going on.

As someone who designs engines, I work from the torque perspective. Like it or not gruntguru torque is a more fundamental concept with regards to engine performance. Its trivial to measure torque output and everything else can be calculated from that.

I will concede that the average guy on a rolling road would prefer to do it by the power method though as it is easier given known real world variables. F=P/S is a far simpler calculation in the real world than knowing the gearing ratios. For what I do, its more simple the other way round.


Either way you try to bullshit around it, power (as its generally understood by science) is not a force and cant be directly felt as such. Torque is. Only people with a crass lack of scientific knowledge say otherwise.

This is why I prefer working with torque to work out thrusts of a wheel. Force in, force out.




And can you please stop saying that jets (and by jets I assume you mean engines operating on the brayton cycle) have power coming out with no torque, the work out from a jet comes in the form of a turbine, which operates on a flow past it creating a turing force (TORQUE). The power output comes from how quickly this spins. The THRUST out is something else alltogether.

I will concede that you did acknowledge that power and work are the main outcomes any a heat cycle, I also agree that torque doesnt have to be the work output from the engine. But without any work done how can you define the power output? The same hold true for otto and diesel cycles.

Also i'd like to point out that you wave around the word power almost arbritrarily. So far in previous posts you've used it to describe both heat and work. This is my problem with what you have had to say, these words acutally mean something and you are not using them correctly.

Hi engine designer

Ramjet

No torque. Lots of power. Please read up on physics.

I also said that torque doesnt have to be the work output. Reading comprehension lessons needed.


EDIT: Ramjets are also a semi special kind of case of the Brayton cycle. Requiring super sonic flow for compression. Got to to get up far earlier than that to be a smart arse.
DOUBLE EDIT: I also found gas tubine cycles to be rather dull.

Damn! you enjoy semanitcs dont you, and sadly I know im going to have to yield on pretty much everything here.

I'll have to concede torque is a force and moment applied at a that tend to rotates a body. I would clarify that I did mean force in terms of 'comething that can be felt'.

Turbine work is indeed work output, just the same as a compressor requires work input. For engines yes the turbine is designed to fulfil the requirements of the compressor only. I did say ealier about torque not being the only output.

Ok its torque*angle turned if your going to get picky about scalar and vector quantities.

And per unit time, yes you dodged the bullet there.


I can see you being a formidable adversary mr grunt.

All you are saying is that as long as the vehicle is moving the engine must be producing power as well as torque. Well sure, but power and torque also two different properties which can be distinguished. The force you feel pushing you back in the seat tracks the engine's torque curve, not its power curve. For example, beyond the rpm of greatest torque the vehicle continues to accelerate but at a reducing rate, even as engine power increases. And yes, this is easy to prove.

Please review your quotation above. Notice anything? It's totally blank, due to your practice of quoting and then replying within the quotation brackets when you post. So when I in turn attempt to quote in reply, I recieve a set of code brackets with no text within them. Nothing, just as in the above. This is annoying and not worth my time to sort out in order to fashion a reply, what with all the backtracking, copying, pasting, etc. required.

So if you desire a reply, please post in a sensible and considerate manner, following the established conventions of this bulletin board format. Do not type within other posters' quote brackets. Quote a post, then reply above or below the quote brackets. Thank you.

You first. As with any reaction engine, the essential property produced by a ramjet is thrust, not power. As with any air-breathing reaction engine, its power rating is indeterminate independently of airspeed. Thus it is that jet engine people are not terribly interested in a jet engine's power, but primarily its thrust rating. Thrust in a reaction engine can be accurately described as the direct analogue of torque in a piston engine.

That's telling him. I'm counting on you to be the last man standing. Whats with this impostor, chris? Take care of him, please. His got no manors. Sounds like another Bolshevik to me.

Anyway, jet engines have plenty torque. The pilot adjusts thrust by monitoring a torque gauge in the case of a propeller or a rotor which is attached to the turbine..

Electrically the 'volt' is analagous to torque/force, yet it is defined in terms of power....

Paul

Silence bourgeoisie scum.

On another note it was not my intentionto be rude, I do tend to come off as such at time though. Its my opinion that this thread has run in circles for a while, with the phrase "No but," being used repeatedy by two sides that are argueing essentially the same thing from different sides.

The bottom line is gruntguru is making power out to be something its not in reality. Technically he is worng about some of the things he has asserted along the course of this thread (if I have the time or inclination i'll go through and find them). Sometime his assertions have been unwarranted, i'm going to read them more thoroughly this time as to not be caught out by minor details again.

As a case of the futility of this thread and the pettyness of the arguements I direct you to the inital post that necro'd this thread.



"FAT BOY "I did simulations to show that the actual acceleration of the car based on these engines was not going to be a based on the engine torque, but engine HP."
--------------------------------------------------------------------------------

MCGUIRE "Not possible. The acceleration of a wheel-driven vehicle is resultant to the thrust available at the drive wheels, obviously. The relationship between engine torque and hp relative to engine rpm is cast in stone. It is a simple matter to calculate drive wheel thrust from either power or torque. Both will produce the identical answer. If they do not, you are doing your sums wrong."

"Sorry McGuire but you are wrong here. Power and vehicle speed are all you need to calculate traction force available for acceleration. Torque and vehicle speed does NOT allow calculation of traction force UNLESS you also know the engine speed or the gearing (either of which will also allow you to calculate the POWER which is the engine property which determines the acceleration available)"

Fat Boy was asserting that he was going to use Hp and not torque to calc acceleration. This could be read as though torque were not deemed importantm, which im sure was not what Fat Boy meant.

McGuire simple pointed outthe fact that acceleration could be calcualted using both power or torque. Which is true. The not true was unwarranted at the start of his responce

Grunt then made the assertion that this was incorrect, before describing that acceleration can be calculated from power using one set of variables. Or torque and some other set of variables, and NOT vehichle speed. McGuires respone lacked that clarification that different variables were needed (but this was stated numerous times earlier in the thread so it was crystal clear what he meant). That lack of clarification does not make the statement incorrect, merely incomplete.

Three arguements, all saying essentially the same thing all greeted with the 'NO WAIII'. Grunts answer was the most complete of the three, but all were valid.

I still lurk regularly but quit posting in this thread when I saw that we will continue to NASCAR -- go around in circles.

Greg, haven't seen much of you on Eng-Tips, on the other hand. I trust all is well with you.

This week I just became the owner of a 1994 Audi 100 S4 Avant 4.2 V8 Quattro (man could a car designation get any longer???). Link. Sorry for the OT. Back to your regularly scheduled NASCAR program.

I think a more apt analogy would be that this thread is like a vortex: it goes in circles and constantly sucks in new victims.

Sorry McGuire. I do this so I can respond point by point when a poster makes a large number of assertions within the one post. You could try copying the original post to the clipboard then pasting into your edit.

I will try to avoid doing it although this sometimes means a lot of posts.

I have re-posted below so you can respond (or slash, burn, annihilate etc)

"

And can you please stop saying that jets (and by jets I assume you mean engines operating on the brayton cycle) have power coming out with no torque, the work out from a jet comes in the form of a turbine, which operates on a flow past it creating a turing force (TORQUE). The power output comes from how quickly this spins. The THRUST out is something else alltogether.
"

A ramjet is a jet and it has no torque.

That quote above is what I was responding to.

Read for comprehension indeed.

Originally posted by xxchrisxx
Either way you try to bullshit around it, power (as its generally understood by science) is not a force and cant be directly felt as such. Torque is. Only people with a crass lack of scientific knowledge say otherwise.[b]
Scientific knowledge? Torque is not a force. It is the vector cross product of force and moment arm.

[b]And can you please stop saying that jets (and by jets I assume you mean engines operating on the brayton cycle) have power coming out with no torque, the work out from a jet comes in the form of a turbine, which operates on a flow past it creating a turing force (TORQUE). The power output comes from how quickly this spins. The THRUST out is something else alltogether.
Turbine work in a jet engine is not an output. It is used internally to drive the compressor. The output from a jet engine is thrust (yes it is a force this time) the linear equivalent of torque. The power output from a jet engine is the product of the thrust and the velocity of the gas jet.

I will concede that you did acknowledge that power and work are the main outcomes any a heat cycle, I also agree that torque doesnt have to be the work output from the engine.
Torque is never the work output of an engine - it is a totally different thing although it has the same units. Torque is a twisting version of force - work is mechanical energy. Torque is the vector cross product of force and displacement - work is the vector dot product of force and displacement.

But without any work done how can you define the power output? The same hold true for otto and diesel cycles.
If you only have torque, there is no work done. You must also have angular displacement. Crankshaft work is the vector dot product of torque and angular displacement.

Also i'd like to point out that you wave around the word power almost arbritrarily. So far in previous posts you've used it to describe both heat and work. This is my problem with what you have had to say, these words acutally mean something and you are not using them correctly.
Sorry to disillusion you but power is defined as the rate of transfer of energy - be it mechanical energy, electrical energy or heat energy. For example - next time you buy a heater you will find it has a power rating in kW, BTU's or whatever.

Static thrust without power is meaningless. Dynamic thrust (thrust available at a given airspeed) is determined by engine power.

A high bypass turbofan has very high static thrust but the exhaust velocity is relatively low so the available thrust reduces quickly as airspeed increases, making it unsuitable for high speed (supersonic) aircraft.

A turbojet designed for supersonic flight will have less static thrust but higher nozzle velocity so thrust will decrease less rapidly as airspeed increases.

The upshot of all this is that power (thrust x nozzle velocity) is an important property of jet engines without which, the appropriate engine cannot be selected.

The high by pass function is used at low altitudes only.