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Hdxbones
| | Posted on Tuesday, November 12, 2013 - 02:33 am: | 
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Torque is a rotational force. Static or dynamic. To be clear, and for the purpose of this discussion, let's just discuss measurable dynamic torque as it relates to engine output.
An engine's HP rating is nothing more than a calculation derived from measured torque.
HP= Eng RPM x measured TQ / 5252
An HP calculation is a great tool to tell what an engine's max potential is. It's a good tool to compare one engine to another. And if all we are concerned about is redline performance, then it's the perfect number to work with.
But we were discussing acceleration in 5th gear at 60 mph. About 3000 rpm. Around 65 ft lbs TQ on most stock XB12 dyno charts that I've seen-
65 x 3000 / 5252 = 37.12 available HP.
Hardly the 103 ponies that everyone likes to talk about.
Suppose I switch to XB9 primary gearing and raise my RPM 300 or so at the same forward speed-
65 x 3300 / 5252 = 40.85 available HP
Suppose I drop a gear, and add 500 rpm-
65 x 3800 / 5252 = 47.02 HP
Imagine that, without changing a thing in or on my engine, I gained 10 calculated HP at the same speed just by increasing rpm at the same TQ output. Suppose I reprogram the ECM and raise my redline rpm for the same TQ output? Suddenly my 103 HP engine becomes 110 or 120 HP. But did it change my performance at 60 mph and 3K rpm. Not at all....
The torque curve across an RPM range is the true indicator of available power. It's easy to see on a dyno chart, and and to make comparisons to other runs. Torque is the measurable force that creates and maintains velocity. Horsepower calculations don't tell the entire story.
103 max HP on the Uly, or max HP on any other bike/car/truck is a sales pitch. I don't ride my bikes at redline very often. I don't ride them at 100% throttle very often. I do ride them at part throttle and mostly at 1/2 of redline or less. Maybe we're skinning the same cat 2 different ways here, but no one ever refers to part throttle, or mid-rpm HP numbers. Calculated max HP ratings are irrelevant, and mean nothing in those ranges. Available, measurable, actual torque at specific rpm's does.....
(Message edited by hdxbones on November 12, 2013)
(Message edited by hdxbones on November 12, 2013) |
Blake
| | Posted on Tuesday, November 12, 2013 - 10:59 am: |
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>>> An engine's HP rating is nothing more than a calculation derived from measured torque.
That is inaccurate. |
Blake
| | Posted on Tuesday, November 12, 2013 - 11:24 am: |
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Hint: No inertial dynamometer measures torque. They measure only one thing to determine HP, the time interval for the calibrated drum to make each complete rotation. That is the only measurement required to determine power output.
In order to determine the engine torque output, the inertial dynamometer computer must also measure engine speed.
It then calculates the engine torque, T=HP*5250/RPM, the exact opposite of what you've asserted.
Some brake type dynamometers do measure torque and the opposite is the case. So you aren't entirely mistaken. But the issue is academic.
When you say that "the torque curve across an RPM range is the true indicator of available power", what you are saying is that the combination of torque and engine speed (horsepower) is the true indicator of available power.
No one is saying that only peak HP is important. Just that In knowing only the horsepower the dynamometer plot horizontal axis may be labeled as percent maximum engine speed, and we would then understand perfectly the power capability of the engine across its entire operating range.
For a chart showing only torque that is not the case. We also need to understand the engine speed at which each to torque value applies to understand the power capability of the engine across its operating range.
(Message edited by blake on November 12, 2013) |
Reepicheep
| | Posted on Tuesday, November 12, 2013 - 01:05 pm: |
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HDXBones... I could build you a motor that will create 100 foot pounds of torque, and that would run off a 9 volt battery. It could be built from a cell phone vibrator motor and a gearbox.
How much would it be worth, and how much fun would it be to ride a motorcycle it powers?
I agree that "peak HP" isn't a great measure of a motorcycle motor. But a peak torque value is even more useless. An HP curve versus RPM is what really tells the story of performance. |
Hdxbones
| | Posted on Tuesday, November 12, 2013 - 02:10 pm: |
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***In order to determine the engine torque output, the inertial dynamometer computer must also measure engine speed. ***
That is not entirely true. The inertial dynomometer measures the rate at which the calibrated drum accelerates in order to determine the force being applied, independent of engine rpm. The dynomometer doesn't care what the engine's speed is, only the drum's rpm and rate of acceleration. One can run a sweep in any gear they choose. The resultant output is the force (torque) being applied. The data point recording of the sweep can be overlaid on any graph one desires. Typically, it is plotted across the corresponding, simultaneously recorded, engine rpm axis. The result is the TQ 'curve' or trace. The engines HP is generally also calculated from those 2 data points, and shown scaled (where HP passes through TQ at 5252 rpm) as well.
It doesn't matter if TQ is measured on a calibrated drum dynomometer, a water brake dyno, or an eddy current brake dyno, HP is still calculated the same way.
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***When you say that "the torque curve across an RPM range is the true indicator of available power", what you are saying is that the combination of torque and engine speed (horsepower) is the true indicator of available power. ***
That is not what I'm saying. The shape of the TQ trace, overlaid on a corresponding rpm graph, is what I'm saying is the real indicator of available power. As I explained earlier in this thread, changing a gear(rpm) will change the calculated HP at any given forward speed(assuming that TQ remains constant across that rpm change).
Knowing the shape of the TQ curve as it relates to engine rpm is where one would find peak efficiency and/or best performance-
-Is there a dip in TQ at a given rpm that I'd want to avoid operating in?
-Is there a high spot in at a lower rpm that would be beneficial for cruising?
-Is there a plataeu that would provide best performance?
-Where is the point of diminishing returns(where does TQ drop off far enough that efficient power is no longer being made?
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***For a chart showing only torque that is not the case. We also need to understand the engine speed at which each to torque value applies to understand the power capability of the engine across its operating range. ***
Correct. My point exactly. And the calculation of TQ value at any point on that graph multiplied by engine rpm at that precise point and then divided by 5252 will tell you what the HP is at that precise point.  }
(Message edited by hdxbones on November 12, 2013) |
Buewulf
| | Posted on Tuesday, November 12, 2013 - 03:51 pm: |
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Way to chum the waters there Reepicheep!
Guess I'll put in my .02:
1) Clearly, Hdxbones did not mean that HP was some fictional number that only exists on paper.
2) Whether you measure work to extrapolate torque and calculate horsepower on an inertia dyno or use torque and engine speed to calculate horsepower on paper, what difference does it make? Give someone a torque figure and engine speed from your dyno run, an he'll calculate the exact same hp for that engine speed that got plotted on that dyno run because it is the same math.
3) A torque curve and a horsepower "curve" are two side of the same coin. However, I think what Blake and Reep are getting at and what I agree with is that the horsepower graph is the more useful of the two since that is what you want to maximize at ANY rpm, speed or throttle position to get the most out of your scoot. The amount of torque available, while related, is irrelevant. Any useful information (dips, flat spots, etc.) in a torque curve are reflected in a horsepower curve as well, so a torque curve doesn't add anything useful. The horsepower curve is the real indicator of available horsepower. |
Motorbike
| | Posted on Tuesday, November 12, 2013 - 05:40 pm: |
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I think I'll just stick with my good ol' seat-o-the-pants dyno. Much simpler. If I crank the throttle on and I feel the bike trying to slide me off the back, all is good!  |
Reepicheep
| | Posted on Wednesday, November 13, 2013 - 11:49 am: |
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Not chumming, we have just hashed the argument out before.
quote:An engine's HP rating is nothing more than a calculation derived from measured torque.
This is the common position we are struggling against. It goes all the way to Carol Shelby, so its no wonder people may interpret it wrong. I think Carol knew what he meant, but I'm not sure everyone that repeats him does.
You are right Beuwulf, the root of this issues is that horsepower and torque are very inter-related. From a motorcycle standpoint, you actually can do a reasonable but fairly limited inference of one to the other.
But from a mathematical and motorcycle sense, the most accurate and meaningful measure of power of a motorcycle is, well, power, expressed as horsepower.
quote:That is not what I'm saying. The shape of the TQ trace, overlaid on a corresponding rpm graph, is what I'm saying is the real indicator of available power.
So you are saying that torque, when combined with velocity (expressed as RPM), is what is important?
Torque alone is not useful. RPM alone is not useful. Torque at an RPM is what is necessary to have a meaningful discussion.
There is a mathematical term for torque (force) at at an RPM (velocity). We should just use that term when we want to discuss power.
Once we get the basic math right, and understand what power really is, then we *can* start to get into what is really important and that people are trying to describe when they start arguing about "torque is what makes a bike fast off the line". And this is important, as it is why I love my 91 HP Ulysses far more than I would love a 120HP GSXR-600...
At the end of the day, it's not about a faster bike, it's about a less annoying fast bike. It's the character of the power delivery.
On a Buell and other "high torque" motors, there is a "shot from a rubber band" sense of acceleration. From low RPM, just off idle, you can whack the throttle and get this kind of "launched" feeling where there is ample power at low RPM. It doesn't make the bike faster (as the other bike can just drop down two gears and do the same launch but at higher RPM and higher power). But it makes the bike more... well.... fun.
The acceleration of an inline four is more like a turbine spinning up... slow at first, gaining momentum, building and building. Nothing wrong with that, I flew out of Atlanta last night and the continued relentless acceleration from nothing to 30,000 feet was a hoot for a gearhead.
But on a motorcycle, I much prefer the instant drama free "coiled spring" like kind of launch. I don't have to drop two gears and make bike noises like a 16 year old with a starved ego and feelings of inadequacy. I gracefully crank the throttle and the bike just kind of squats and springs forward. Many other people like this better as well.
Of course my XB12X will do an absolute faceplant at 6800 and 1 RPM (or wherever it cuts in the rev limiter). The GSXR-600 is just getting fun at about that RPM. But I, in general, feel like an idiot riding around at 6800 RPM. Purely a personal preference thing.
So the Buell isn't better because it is making more power (it isn't). It is better because it gives me the power I want with the character (instantly accessible at low RPM's) I prefer. That's all.
Calling these motors "high torque" motors is accurate, because that is how you get high power at low RPM. Just don't kid yourself and think that high torque means more power. It is the product of torque times RPM that means power, and more is more is more period. From a power standpoint, it makes no difference if you have twice the RPM but half the torque, or twice the torque but half the RPM (until you start to getting into discussions about how often you want to shift, but that's yet another different but related topic).
So I think I actually agree with HDXBones conclusion, we are just disagreeing about how to express the underlying math. Not a big deal, but if we can be precise about the math (which is precise) there are a lot of little gems waiting to be discovered that you can't find with intuition and rules of thumb alone.
A plot of HP versus RPM is the clearest and most succinct chart to demonstrate what kind of acceleration that motorcycle is capable of.
I'll close an overly long and preachy post with an apology and a final analogy.
The Buell 1125 makes 82 foot pounds of peak torque. The Buell XB12 makes 84 foot pounds of peak torque.
Line both bikes up at about 20 MPH coming out of the keyhole at Mid Ohio onto the back straight. Whack both throttles wide open and accelerate to the far end (or until you chicken out, I did, I was in a textile suit). Since the XB12 makes 84 foot pounds, and the 1125 makes 82 foot pounds of torque, the XB12 will get to the other end first, right?
(Hint... I have a GPS plot showing me at over 150 MPH on an 1125... My XB12 won't hit that unless I ride it out the back of an airplane). |
Hdxbones
| | Posted on Wednesday, November 13, 2013 - 05:18 pm: |
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quote:So you are saying that torque, when combined with velocity (expressed as RPM), is what is important?
Torque alone is not useful. RPM alone is not useful. Torque at an RPM is what is necessary to have a meaningful discussion.
There is a mathematical term for torque (force) at at an RPM (velocity). We should just use that term when we want to discuss power. ; )
Yes sir, that is exactly what I'm saying.
It's just that I find it more informative to review the basic data(TQ trace) as opposed to the compounded data(HP calculation).
It seems we all agree that increasing rpm for the same TQ value results in more calculated power(HP). When reviewing a TQ curve, that should be a given. But converting the TQ curve into just an HP curve dilutes the data, and frequently masks or minimizes useful information. Here's a random run file that I found on this forum, it's not a reflection of anyone's work, and is only being used for discussion-
If I look at just the calculated HP trace, I see a small anomaly from 3500-3600 rpm. It hardly looks to be an issue. Maybe it's not. But if I look at that anomaly on the TQ trace, I can see that I've lost 6 ft lbs of TQ from 3000 rpm to 3600. And that I don't get back to where I started until about 4400 rpm. But HP keeps climbing, what's the big deal some would say? The big deal is that this particular engine is LEAST efficient in the exact rpm range that most street riders would spend 90% of there riding time. If that were my bike, maybe I'd want to find a way to make it more efficient in that range; perhaps a new fuel map, or a different exhaust,or intake, etc. If I can remove that valley from the TQ curve, my corresponding HP would rise at a much steeper rate. Right where I ride the bike the most.
But I can only see that on the torque trace, the purer form of data. The calculated HP trace waters the information down, it softens the edges. The devil is in the details, and it's my opinion that just looking at the HP calculation is not detailed enough.... |
Buewulf
| | Posted on Wednesday, November 13, 2013 - 06:39 pm: |
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Fair enough.
But looking at the power graph, I see more than a small anomaly - HP has been reduced. You look at the torque curve and see that there is a big dip that needs to be "fixed". However, I can tell by the power curve that it really isn't an issue beyond 3750 rpms where the power comes back online. A butt dyno would confirm that as well. I'm not saying more torque everywhere wouldn't be better, just that the problem area is much smaller that the torque curve would suggest and that it doesn't provide "purer" information - just different information.
Since we typically look at both graphs plotted together anyway, I suppose this discussion is 95% wasted electrons. We should make a chart for that. So, do you think it would be better to plot amps or watts to better get a grip on our uselessness? |
Blake
| | Posted on Wednesday, November 13, 2013 - 09:08 pm: |
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>>> The inertial dynamometer measures the rate at which the calibrated drum accelerates in order to determine the force being applied, independent of engine rpm. The dynamometer doesn't care what the engine's speed is, only the drum's rpm and rate of acceleration. One can run a sweep in any gear they choose. The resultant output is the force (torque) being applied
Not so much. Without knowing engine speed the Dyno computer cannot calculate the torque. Without the ignition sensors, all the Dyno chart trace will show is HP vs ground speed or time. If you want to know the engine torque, the computer must also know the engine speed. |
Blake
| | Posted on Wednesday, November 13, 2013 - 09:15 pm: |
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I agree with the utility of using the torque trace for scrutinizing and tuning. I don't think anyone was arguing against that. |
Reepicheep
| | Posted on Thursday, November 14, 2013 - 08:00 am: |
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Great discussion, thanks! |
Hdxbones
| | Posted on Thursday, November 14, 2013 - 02:24 pm: |
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quote:Buewulf -
But looking at the power graph, I see more than a small anomaly - HP has been reduced. You look at the torque curve and see that there is a big dip that needs to be "fixed". However, I can tell by the power curve that it really isn't an issue beyond 3750 rpms where the power comes back online. A butt dyno would confirm that as well. I'm not saying more torque everywhere wouldn't be better, just that the problem area is much smaller that the torque curve would suggest and that it doesn't provide "purer" information - just different information.
I think many of us look at dyno run files, and tend to focus on the peak results. What is the max HP and TQ, and where is it achieved? What does the 'curve' look like that got us there? Is my bike more powerful than 'X' brand? Or my buddy's bike? Or, did this $1000 exhaust and ECM produce any tangible results?
While those are all relevant and useful questions, I think that they're only a small part of the story. On the run I posted above, max TQ was achieved around 6000 rpm, max HP at 6800 rpm redline. Fairly common results for any bike, TQ peaks a little before max rpm, and HP climbs until redline. Most dyno tuners focus on the peak numbers as well, trying to sell results. But how often does your bike see redline rpm on the street? Mine gets there rarely. Having an extra ft lb or HP or two at 6500 rpm does little for the way I ride my bike.
I spend almost all of my riding time below 5000 rpm, and most of that below 4000 rpm. That's where I want my bike to run the best. I want instant acceleration, correct fueling, no stumbles or backfires, and best fuel economy in that rpm range. So if I gloss over the TQ dip that we looked at above, content that my engine recovers it's losses after 3750 rpm, I've given up desired performance exactly where I would want to have it most. I generally try to base decisions about my bike's performance and tuning modifications with those results in mind, rather than peak performance.
Or maybe I don't want to do anything about it. Just knowing that I have diminished performance in the 3000-3500 rpm range is valuable all by itself. Armed with that, I would select gears and fwd speeds that minimized my time in that area. For fuel economy, I'd try to stay below there, for spirited riding in the tight stuff, I would want to stay above it.
So really, the TQ curve above does highlight an area of great importance to me. And for me, the problem area is exactly what the TQ curve indicates, certainly not smaller. And at the risk of sounding repetitive, the detailed view is not clear on the calculated HP trace.
Certainly, there is much more to it than that. Throttle position for individual runs, gear choice, ambient conditions, type of dynomometer, AFR trace, etc. all factor into the equation.
So with that said, I've had my Uly for a year this week. And it's still bone stock. And I'm trying really hard to leave it that way(it's not easy) . Except for an occasional off-idle stumble, it runs really well. I do think I might try the XB9 primary gearing to move the TQ curve further down the rpm range, I'd like to have a little more ride-ability and engine braking, with less clutch work out on the trails. |
Buewulf
| | Posted on Thursday, November 14, 2013 - 05:41 pm: |
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I think we actually all agree and that this has really just become academic! I'm just saying the information between the two charts is different which I think is exactly what you are saying. Like I said, I always look at both, and the usefulness of one or the other is dependent on what I am attempting to achieve.
I have never dynoed my bike, but I am certain it is shaped just like the chart you posted. I can feel it as I accelerate through the gears. The bike is a vibey slug below 3000rpm, so I am never in that rpm zone. I try to keep it above 4K at all times because that is where the usable power begins. I'll click it into 5th if I'm droning along a highway, but not otherwise. I have also been tempted by the gearing change, but I don't get great fuel economy as it is due to my riding style. And the Uly's range is around the minimum I accept from this kind of bike. |
Kenm123t
| | Posted on Thursday, November 14, 2013 - 07:34 pm: |
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I'm making popcorn for this thread Its almost as good as an Oil thread! |
General_ulysses
| | Posted on Friday, November 15, 2013 - 10:01 am: |
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You can slice it any number of ways, but in the final analysis, you can’t isolate just torque or just power and define one or the other as being “the most important.” Power is simply = torque x rpm. Period. It can be expressed in different ways (like force x velocity) or using different units (metric vs standard etc), but that’s what it is. Period. Power is inextricably linked to torque, the two are directly related to one another.
As a brief aside, “one horsepower” was originally created as a way to measure a commonly understood unit of power. In the old days before the automobile, most everyone had a general understanding of a horse’s power, so it was used as a common reference for denoting the power of industrial steam engines, IC engines and early electric motors.
One horsepower was defined by taking a sampling of horses (all of them being somewhat different, of course) and coming up with an average power capacity. They put a harness on that “average” horse, hooked a rope on him and then ran the rope through a simple pulley and then down to a weight that was positioned to lift off the ground as the horse walked forward. They found the average horse could lift about 550 lbs, 1 foot off the ground, in 1 second. Or 550 foot*lbs per second (1 hp = 550ft*lbs/sec). That’s the rate at which your average horse could accomplish that amount of work within one second. In reality, the power output of horses varies widely, and a lot of horse people argue about the validity of this number. But the point is that it was a common reference that everyone agreed to for the purposes of rating power (i.e 1 hp =550ft*lbs/s).
Notice how when 1 horsepower was defined through those experiments with how much weight a horse could lift in a second, that no torque was applied? The formula used for calculating that power was force x velocity. But you can also express power by replacing force with torque and (linear) velocity using angular velocity. Angular velocity can be expressed in many different units, but is most commonly expressed in rpm for reciprocating engines. So power coming from a motor with a rotating shaft (instead of a horse pulling on a rope) is measured using torque x rpm. That horse can be replaced with a motor with a shaft that is also capable of producing 550 ft* lbs/sec. It may need a gear reduction device because it spins the pulley too fast to directly achieve lifting a 550 lb weight, 1 foot off the ground, in 1 second, but a 1 hp motor can do the equivalent amount of work as the horse.
Getting back to cars and motorcycles, I think a lot of the confusion over the importance of torque vs power comes out of a misperception of the two. In reality the two are interlinked, they cannot be thought of separately. There’s an old saying “torque wins races, horsepower sells cars.” But that isn’t really true. Power is what moves your car or motorcycle forward, and without it, you won’t be winning any races. The real issue is USABLE, TRACTABLE power. There are engines for motorcycles and cars that can achieve terrific peak horsepower numbers compared to other similarly sized engines with less max power. But their power delivery is very peaky and often delivered within a very narrow rpm range (usually near or at redline). The power output in low to mid-rpm range can be very lackluster. These limitations in practical terms make for a car or motorcycle that is hard to drive or ride in a way that wins races. Keeping the engine within that narrow rpm range to achieve maximum power can severely limit the practical usefulness of that otherwise impressive peak power. That’s why an engine that may produce less peak horsepower, but delivers solid low end and mid range power (and torque!) over a much broader rpm range, can in fact win more races than the higher peak hp primadonna.
The Buell/Harley V-twin is a very good example of an engine that doesn’t develop the maximum peak hp of similarly sized, modern inline 4 cylinder engines. But in exchange for that offset in max power, it provides that luscious torque delivery we all know and love – and that can be very visibly seen on those performance graphs posted earlier. But really it isn’t just torque that it delivers. It delivers that large amount of torque throughout a broad rpm range, which by definition means it is actually delivering a broad, widely distributed power output. On the race track, especially a twisty one with fewer sustained straights where maximum power cannot be consistently applied without crashing, that flat, broad power/torque delivery makes for a higher performing motorcycle with faster lap times. On the street it’s an easier and much “funner” bike to ride through the twisties.
All my life I’ve ridden Japanese bikes and none of them were V-twins. This spring I got my Uly and now I fully understand and appreciate just how fun the big V-twins really are. I have no interest in racing, but I can certainly see now how their power delivery would work extremely well going in and out of a series of turns. Usable, tractable power is what matters. |
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