| Author |
Message |
    
Buell_41
| | Posted on Monday, October 29, 2007 - 09:20 pm: | 
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Ok, did some searching around the KV but didn't find quite what I was looking for. If 1st gear is a torque multiplier why aren't tests for torque done in 1st and maybe tests for HP done in 5th. I know that the two are related and I understand what the two are. It just seems like if you want to see how fast you could go (horsepower) you'd want to see how fast an engine could spin the wheel on the weighted dyno, you'd do it in 5th. Torque in 1st.
What am I missing? |
Diablobrian
| | Posted on Monday, October 29, 2007 - 11:47 pm: |
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All torque measurements are considered to be at the crank due to the way the formulas work
so no matter what gear you are in the torque values remain the same for a given RPM and
throttle opening no matter what the gear ratio is.
I had a hard time coming to grips with this one initially too, but the math proves it out.
The major downfall of dyno testing and tuning for the street is actually the lack of attention
to any throttle position but WFO. |
Aesquire
| | Posted on Tuesday, October 30, 2007 - 06:26 pm: |
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5th gear with a Tuber or XB trans. is 1-1. Minimum loss from gear friction. |
Buell_41
| | Posted on Tuesday, October 30, 2007 - 09:27 pm: |
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I understand that the engine puts out a certain amount of torque. But as you go through 1st gear, its stepped up. The gain is more than the output of the engine alone even with losses... 5th gear would seem to have the least mechanical advantage... least torque. |
Diablobrian
| | Posted on Tuesday, October 30, 2007 - 10:00 pm: |
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The idea is to measure actual torque, not applied or perceived torque.
It would be easy to artificially inflate torque numbers by gearing ultra low if the gearing
was not taken into account.
Kind of like the old adage: you could move the world if you could just find a long enough lever.
That wouldn't make you stronger physically, it would just multiply the force you apply.
A lighter wheel and tire gives the appearance of more torque (and therefore HP) as well, but it
is really an illusion if no other changes were made.
Seeking peak numbers is not the true value of a dyno run, finding and fixing holes in the HP
and Torque curves is where the real value lies.
(Message edited by diablobrian on October 30, 2007) |
Blake
| | Posted on Wednesday, October 31, 2007 - 02:01 pm: |
|
What Brian said.
Plus some more discussion, on account of I dig this stuff. 
In order to determine RWHP, a rear wheel or "chassis" inertial dynamometer only need measure the successive time intervals for each rotation of the drum. Using that time interval data (drum rotational velocity) and the known physical properties of the drum, the drum's acceleration is determined, and from that the HP being exerted upon the drum by the rear wheel/tire is calculated.
With the result of that RWHP calculation, the corresponding known/measured engine RPM for each time interval may be used to calculate the engine torque as referenced to the rear wheel. "Referenced to the rear wheel" means that the true torque of the engine at the crankshaft is not what is being reported. What is being reported is the true torque at the crankshaft minus all the parasitic drivetrain losses between sprocket shaft and the rear tire contact patch.
The actual torque at the rear wheel (thrust at contact patch times radius from contact patch to rear axle) may be found by multiplying the engine torque referenced to the rear wheel, by the overall gear reduction ratio of the drivetrain (primary drive x transmission gear x final drive).
Or you could rig a sensor and trick the dyno into measuring rear wheel RPM instead of engine RPM.
One interesting thing to note is that torque and HP as reported by a chassis inertial dynamometer will vary slightly from one gear to the next, increasing slightly with each successive upshift.
This is due primarily to two effects, the varying rate of acceleration and drivetrain loading. With each upshift to a higher gear, the gear reduction ratio decreases, which in turn equally reduces the loading/torque transferred to drivetrain components that are downstream of the input side of the transmission's mainshaft to countershaft engagement. The reduced load will improve efficiency of power transfer between mechanical drive components (gears, sprockets, belt, rubber tire contact patch).
Also the engine's crankshaft/flywheel/output sprocket/generator rotor rotating assembly act as a pretty darn effective dyno drum in itself, so spinning the engine up less quickly like when accelerating in a higher gear, robs less HP thus allowing more HP to reach the rear wheel and ultimately the dyno drum.
And of course when in 5th gear, the drivetrain torque is passed straight through the mainshaft of the transmission, avoiding the countershaft and thus mechanical power transfer through two additional gear pairs.
So, if you want to achieve max dyno peak HP and Torque results on an inertial dynamometer like the popular Dynojet series, You'll want a good hard tire (less lost power to tire flexing), that is well worn (reduced inertia/mass, meaning dyno drum effect), and at maximum pressure (less tire flex), a thoroughly warmed up transmission (reduced oil viscosity reduces parasitic power loss), run it in 5th gear (most efficient for drivetrain and for power-robbing inertial effects), only apply minimal downforce to rear of bike, just enough to maintain traction on dyno drum (reduce tire flex), ensure that while under full power, the bike is positioned on the dyno so that the rear axle is directly/vertically over the dyno drum's axis (reduce force on tire and thus tire flex).
I may have missed some.
(Message edited by blake on October 31, 2007) |
Jackaroo
| | Posted on Wednesday, October 31, 2007 - 03:36 pm: |
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Hi
Sounds like everyone is talking Inertia dyno's.
In the case of an Inertia Dyno, Force at the rear wheel/drum interface is calculated.
Force and drum rpm are used to calculate hp at the rear tire/drum interface.
HP and engine rpm are then used to calculate engine torque.
The "problem" with an Inertia dyno is the rwhp is quite low because as well as accelerating the drum all the rotating parts of the bike have to be accelerated, rear wheel, clutch crank etc etc etc. Dynojet have "correction factors" to bring the figures up to what they think they should be. From this you can see easy hp gains by fitting a lightweight rear wheel, light clutch, crank etc.
A brake dyno measures drum torque and rpm, calculates hp with hp=torquexrpm/5252.
This hp is used in conjunction with engine rpm to give you torque at engine rpm.
You may have noticed some dyno graphs which have hp and mph as the graph axis, this is why.
When Mark Dobeck and his team were developing the DJ they used a VMax as a test mule. They were getting around 85 rwhp on their inertia Dyno, brake dyno about 105 rwhp, and an engine brake around 120 bhp. The 85 they got was actually correct for an Inertia Dyno, a lot of hp soaking Inertia in the VMax, but obviously it didnt look good.
So the solution was to "correct" the 85 to 120. The situation still exists today, even with the 250i. Power runs are still done using Inertia, the brake is only there to enable tunelink to work.
So dont take too much notice when comparing runs, especially if they are from a DJ. You have no idea what the other bike has had done to it. Engine wise they could be the same but wheels tyres sprockets clutch primary etc etc will all make a difference on a DJ.
Its a lot harder to fool a brake dyno.
cheers |
Blake
| | Posted on Wednesday, October 31, 2007 - 05:37 pm: |
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I don't believe that inertial dynamometers require the calculation of any "force". The HP is calculated from measured drum acceleration and known physical properties of the drum. That's it.
And I don't believe that "Dynojet have "correction factors" to bring the figures up to what they think they should be."
Your points concerning the inertial effects of drivetrain and engine components are correct. However, far from being a "problem", that characteristic of an inertial dyno can actually be an advantage. How? It tends to replicate real world acceleration scenarios. Why/how? When accelerating from lower speeds where mass/inertia of the bike_rider, not aerodynamic drag, is the major impediment to acceleration, an inertial dyno may best duplicate the acceleration scheme experienced by the engine and drivetrain.
It's just not often that we ride up to a speed where acceleration ceases or diminishes to a negligible level. That is seen at places like Bonneville, not often on public roads, well not for a 100+HP class motorcycle anyways.
The only correction factors that I am aware that Dynojet uses are environemental. I've heard a few people claim that Dynojet use some additional factors, but since their RWHP numbers are quite a bit below what one sees on an engine dyno, that doesn't make sense. I think it is Superflow that claims that Dynojet cheats on their RWHP reporting. I don't buy it. Too many variable and too much trouble to do so and for no good reason. |
Jackaroo
| | Posted on Wednesday, October 31, 2007 - 08:29 pm: |
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If you go through the math force is calculated before hp. You start with the moment of inertia for the drum, measure the acceleration, calculate the force which brings about that acceleration and then deduce hp.
A brake dyno has one major loss - transmission, churning oil and bending chains etc. An Inertia dyno has the same transmission loss plus rotational inertia losses, rear wheel, sprockets etc. So an Inertia Dyno will always read lower than a brake (same bike, test conditions etc).
http://www.hotrod.com/thehistoryof/113_0603_dynoje t_chassis_dyno/company_creation.html
is a link to an interview Marc Dobeck did with Hot Rod magazine.
When accelerating from low speeds rotational inertia is very small compared to the inertia of the bike, from around 25mph drag overtakes rotational inertia as a significant force.
An inertia dyno can only do constant load sweep tests. ie the load presented to the bike is the same at 8000 rpm as it is at 2000rpm and 4000 rpm. Using your real world example the load at 8000 rpm should be 4 times that at 4000 rpm. Using a modern brake, an exponential load can be programmed in to give a more realistic real world load.
In fact a brake makes a better inertia dyno than an inertia dyno, constant load, constant acceleration, exponential load or acceleration.
I used dynojets for many years (we still have a 250 in the workshop) but since using a brake in the states a few years ago I was sold. We use the dj for general tuning and tuning power commanders. (Although I can generally map a PC quicker on the brake than using tunelink on the DJ) The brake is used for "serious" tuning and problem jobs from the DJ. The DJ is a good dyno, good results most of the time, and for most people is good enough.
From a personal point of view I find I can achieve more on a brake, eg there is no comparison when using the dyno for diagnostic work, the brake wins hands down. A miss at 5000 rpm, straight onto the brake. Dont even bother putting it on the 250 even if its free and we have to wait for the brake.
The point is that if you have only used a DJ you dont know how how good it really is or isnt until you use something else.
Personal opinions of course ! |
T_edinger
| | Posted on Wednesday, October 31, 2007 - 11:10 pm: |
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Blake
Thanks, I actually understood EVERYTHING.
Toby |
Blake
| | Posted on Thursday, November 01, 2007 - 12:21 am: |
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Jack,
Welcome to BadWeB! You sound like the kind of well versed competent professional that I'd very much enjoy following around in your shop and learning a BUNCH from.
Some clarification:
"If you go through the math force is calculated before hp. You start with the moment of inertia for the drum, measure the acceleration, calculate the force which brings about that acceleration and then deduce hp."
If I were doing it, I'd just multiply the angular acceleration times the mass moment of inertia of the drum times the angular velocity and factor to get units of HP. No need to determine the torque or "force" as you say.
I'll give you that Torque, what I assume you are calling the "force", may be found by multiplying the angular acceleration times the mass moment of inertia of the drum, so it is in there. It just doesn't get calculated separately.
No argument that a brake dyno will report higher results than an inertial dyno. My point is that it is not a "problem" as you stated, and that in fact it can be advantageous to replicate real world performance. When you get on your bad motor scooter and accelerate hard in 1st or or 2nd gear, you have the very much the same scenario as on an inertial dyno where significant power is consumed in spinning up the engine, and drivetrain and wheel/tire.
"25mph drag overtakes rotational inertia as a significant force."
That is very difficult for me to believe. Aerodynamic drag at 25 mph is extremely low. The dynamic pressure at 25mph and STD is only about
252/391 = 1.6 PSF (0.011 PSI).
Pushing a very liberal eight square feet worth of that drag loading at 25 mph would consume...
P = 8*1.6 LBs * (25 MPH * 5280 FT/Mi / 3600 s/HR) / (550 LB-FT/s)/HP
P = 12.8 LBs * 36.7 FT/s / (550 LB-FT/s)/HP
P = 0.85 HP
I'd wager that it takes a heck of a lot more power than that to feed the parasitic losses in the engine and drivetrain due to inertial effects when accelerating through 25 mph at WOT in 1st or second gear. For a reality check, imagine your 1 HP weedwacker trying to spin up just the rear wheel/tire.
I don't follow your exponential load comparison. The energy required to spin up the dyno drum also increases exponentially with its velocity, thus so does the power required to accelerate it.
Seems to me that a DJ 250 with a brake would allow diagnosis of your "miss at 5000 rpm" scenario just fine. I agree that a full blown brake dyno may offer some enhanced capability for tuning. It's why they are more complicated and thus cost significantly more and thus are much less prevalent.
The topic here was about why it is desirable to perform Buell dyno testing in fifth gear. I don't know of a Buell dealer that runs a programable brake dyno. Inertial dynamometers are legitimate and accurate machines in the hands of a competent operator. You can mess up the integrity of a brake dyno results in many of the very same ways as you can an inertial dyno (cold engine, cold tranny, low/high tire pressures, excess weight/loading on rear axle, improper positioning on dyno, etc...).
We can certainly agree that a full blown programable brake dyno is a higher grade test machine that offers added capability, no questions there.
(Message edited by blake on November 01, 2007) |
Blake
| | Posted on Thursday, November 01, 2007 - 12:23 am: |
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Thanks for confirming that Toby. It sure is nice of you to say that. I sure enjoy talking tech like this, but it's sometimes hard to tell if anyone else is interested/reading.  |
Buell_41
| | Posted on Thursday, November 01, 2007 - 12:33 am: |
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I'm kinna redneck in the way I think sometimes. But I have to simplify the concepts to understand. So, I like to think of torque as how hard I can slam the table with my hand (because torque is force x distance). Being that its times distance, I have to raise my hand up as far as possible. All the raising and lowering takes time. I can't hit the table very many times. Horsepower on the other hand is like how many times I can hit the table. If I only raise my hand 1/2" off the table, I can quickly go back down. Well I'm not slamming the table as hard as in the torque example. These two senarios sound a lot like I-4s versus twins. I-4s have small strokes, more HP, less torque, more RPM. Twins have larger strokes, less HP, more torque, lower RPM.
Ok, so taking all this into account, on an inertial dyno, if one were to do a run from stop to redline in 1st, it seems like the engine would get the dyno spinning faster... sooner... right? Would the results be skewed? What would the curves look like. |
Jackaroo
| | Posted on Thursday, November 01, 2007 - 02:27 am: |
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Hi Blake
Its all true!! but I'm not bagging DJ, but I do think they are oversold to a certain extent.
A simple test, get some time on a 250i with a torque cell. Use the brake and get a torque reading at say 5000 rpm. Lets say you get 50 ftlb. Run the inertia test and at 5000 rpm you would probably have around 55-60 ftlb. If you hook up a DA unit to the o/p of the drum during the inertia run and do the appropriate math you will have maybe 45ftlb. (You will have to measure the moment of inertia of the drum because DJ wont tell you!!)
All that aside the way I look at dyno tuning is this, the primary aim is to have the bike running as best as it can be, the numbers are secondary. I just find a brake easier to use and more versatile, eg problem area of 5000-7000 I can concentrate on that without having to do sweep tests. While a 250i can be used in the same way the problem (theres that word again) is the brake overheats if you work it too hard. DJ recommend not to use the dyno this way. It is a design problem which is easily fixed but is probably more of a problem for the marketing dept rather than engineering.
On occasion after tuning on the brake we run the bike on the dj. The 15-20% more power on the DJ graph looks good!!!
I dont call dj hp numbers cheating or wrong, I look at them as estimates of crankshaft HP (Marc Dobecks original rationale for correcting the output) whereas the brake output is simply rwhp.
The more you learn the more you dont know
cheers |
Blake
| | Posted on Thursday, November 01, 2007 - 10:28 am: |
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What is a "DA unit." Before you answer, please remember to keep it family oriented here. 
I'm not sure I am reading you correctly. Are you saying that your DJ inertial dyno reports higher numbers than your brake dyno by around 10%?
"The more you learn the more you dont know."
<in my best/haughtiest Harvard (prn. hah'-vahd) accent>... So true, except of course for those of us who really do know it all. 
All kidding aside, you are light years ahead of me in hands-on dyno knowledge. The only dyno that I've ever personally operated was an engine brake-dyno with gages and voltage output only, no computer data acquisition. |
Blake
| | Posted on Thursday, November 01, 2007 - 10:59 am: |
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"I look at them as estimates of crankshaft HP (Mark Dobecks original rationale for correcting the output) whereas the brake output is simply rwhp."
I found the Hot Rod Magazine article where that is mentioned. It's an interesting read.
It might be confusing to call it "correcting" though, as that may tend to confuse the issue with the proper/scientific environmental (air temperature, atmospheric pressure, humidity) correction factor schemes that are available on most modern dynamometers.
Some day, I'll have my own personal shop and chassis dyno to fool around with, just for fun. |
Jackaroo
| | Posted on Friday, November 02, 2007 - 10:03 pm: |
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Hi
da should be daq.
We looked at upgrading our 250i with the optional torque cell so we could use it as a brake dyno. Of course the salesman said no problem but when I spoke to one of the DJ techs he said "yes BUT"
From what I gathered DJ are sticking to their Inertia based system and development will be in conjunction with the companies other products, PC, etc. ie the primary purpose of the dyno is to promote other DJ products, tuning and fault diagnosis is secondary.
It would make good business sense to become an "approved tuning centre" and get little badges for our shirts but not being a corporate type person I am resisting!
Truth be told our 250 makes more $ per hr than our brake because we spend too much time fooling around and playing with things on the brake!! |
Firemanjim
| | Posted on Saturday, November 03, 2007 - 02:25 am: |
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We had to put a Dynojet correction factor in our dyno so the guys that are just concerned with HP numbers won't go away disappointed.Those that just want their bike tuned don't care.
The DJ is certainly easier to tune a bike if it has a Power Commander as you can just download maps right into it and make running changes in maps.
We will look to get a portable DJ if business is good. Now we just book Vallejo dyno if we need it,we still do alot of bikes for them. |
Jackaroo
| | Posted on Saturday, November 03, 2007 - 02:10 pm: |
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"Ok, did some searching around the KV but didn't find quite what I was looking for. If 1st gear is a torque multiplier why aren't tests for torque done in 1st and maybe tests for HP done in 5th. I know that the two are related and I understand what the two are. It just seems like if you want to see how fast you could go (horsepower) you'd want to see how fast an engine could spin the wheel on the weighted dyno, you'd do it in 5th. Torque in 1st.
What am I missing?"
Hey Buell_41
A Brake Dyno measures torque (from the torque cell attached to the drum) and drum rpm. HP is calculated using the formula
HP=Torque x RPM / 5252
So if you ran the bike in a lower gear say 3:1 the torque would be multiplied by 3 (as you correctly said) but the rpm would be divided by 3, HP would remain the same.
At the same time as all this is happening engine rpm is being read. The formula is rearranged to
Torque = HP x 5252 / engine rpm
and the computer can then print out a graph with torque, hp, and engine rpm and irrespective of what gear you use they will all be much the same. Aside from some small gearbox losses because you are using different gears.
Dynojet is much the same except the math is a little more complex and they also factor the results upwards to try and approximate crankshaft hp and torque, whereas the output of a brake dyno is based on rear wheel hp.
Clear as mud?
cheers |
Blake
| | Posted on Sunday, November 04, 2007 - 08:35 am: |
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Even simpler would be to multiply the measured torque at the drum by the overall drive ratio (including dyno drum) which would equal drum RPM divided by engine RPM, both of which are measured by the brake dyno.
After writing the above, I just realized something. The torque about the rear axle, what we have been calling the "torque at the rear wheel" is never measured, not even by a brake dyno. The torque that a brake dyno measures is the torque acting about its drum's spinning axis; it's at the drum not the rear wheel. Unless the dyno drum has the exact same radius as the rear tire's contact patch (from rear axle spin axis), that torque will be different. |
Jackaroo
| | Posted on Sunday, November 04, 2007 - 03:54 pm: |
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yep thats right. the torque will be different everywhere, drum, axle, sprocket, gearbox etc but the rpm will also be different. The point is that no matter where you measure torque, HP will be the same,(aside from losses)
By measuring the drum torque and drum rpm, converting to HP, then using HP and engine rpm you will get engine torque without having to know drive ratios or having to measure the diameter of the wheel. |
Aesquire
| | Posted on Sunday, November 04, 2007 - 06:15 pm: |
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Right! and the least drag on the system is in 5th gear, with the least # of gears to pour power through & the least % of inertial resistance from an already spun fast rear wheel. 50 to 60 is less % than 20 to 30, whatever units you use. |
Blake
| | Posted on Monday, November 05, 2007 - 05:24 am: |
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"By measuring the drum torque and drum rpm, converting to HP, then using HP and engine rpm you will get engine torque without having to know drive ratios or having to measure the diameter of the wheel."
I agree. But I'm not sure we need to do any measuring or that we need to know any drive ratio. Doesn't the dyno measure how fast the drum is turning? And wouldn't the ignition pickup tell it how fast the engine is turning, so there is no need to measure the diameter or know any drive ratios, is there?
It is interesting to note that a brake dyno doesn't actually measure torque. It measures the load (force) being applied at a known distance (lever arm or "moment arm") from the drum's axis of rotation. The torque is calculated by multiplying the reading of the calibrated load cell (force) which is restraining the brake times the distance of its load line of action's radius from the axis of rotation (lever arm). Kind of like if you hooked a chain to a wrench and used the chain to pull on the wrench. The torque being applied to the bolt or nut would equal the tension in the chain, times the lever arm distance, in this case the length of the wrench assuming the chain is oriented to pull at exactly 90o wrt the wrench.
If we want to be precisely accurate, the only thing actually being directly measured at the brake isn't torque or even the force restraining the brake; the force is deduced from a calibrated voltage or resistance measured across calibrated strain gauge(s), just like how a modern digital bathroom scale works. So the dyno is measuring relative voltage, which is proportional to strain, which equates to a stress, which given the geometry of the applicable part then yields a force or load, then given the known geometric relation to the drum's axis provides the torque.
Patrick,
The inertial resistance to acceleration increases with velocity squared, so it actually takes a LOT more power to accelerate the rear wheel from 50 to 60 mph at the same rate as from 20 to 30 mph. Remember KE=1/2mV2 (kinetic energy = 1/2 mass times velocity squared). So wrt the rear wheel itself, since with every upshift the acceleration rate decreases (tends to reduce inertial losses), but the energy required to accelerate it increases (increasing inertial losses) I'm guessing that the rear wheel inertia may be a wash in its effect.
Of course the engine flywheel and output sprocket and generator rotor are all spinning at the same speed no matter the gear, so when accelerating less quickly in 5th gear, the inertial loading is significantly less with more power passing to the rear wheel.
You nailed it though; 5th gear is the most efficient for transfer of power to the dyno drum for an inertial dyno, but also for a brake dyno. |
Blake
| | Posted on Monday, November 05, 2007 - 05:29 am: |
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Hey Karsten. |
Jackaroo
| | Posted on Monday, November 05, 2007 - 12:01 pm: |
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"By measuring the drum torque and drum rpm, converting to HP, then using HP and engine rpm you will get engine torque without having to know drive ratios or having to measure the diameter of the wheel."
"I agree. But I'm not sure we need to do any measuring or that we need to know any drive ratio. Doesn't the dyno measure how fast the drum is turning? And wouldn't the ignition pickup tell it how fast the engine is turning, so there is no need to measure the diameter or know any drive ratios, is there?"
You have been awake too long!!
And yes the torque cell consists of a lever trying to squash a strain guage.
I am glad it is done this way because 20 years ago I had a hydraulic brake dyno. We took pressure readings at various mph (no computer, we used pencil and paper) and then looked up tables to get HP.
A MAJOR advantage, IMHO, the brake has over the dj is due to the relatively low drum inertia we can dyno low power bikes.
Not everyone has 100hp, some dont even have 20hp
Scooters need love too
>>I found the color buttons<<
(Message edited by jackaroo on November 06, 2007) |
Aesquire
| | Posted on Monday, November 05, 2007 - 05:11 pm: |
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Blake, wouldn't the percentage difference between 50-60 be less than between 20-30? It's 10 units either way, and in real world riding Aero effects would really be larger between 50-60 than 20-30, but that's a Cube function. Inertia is a Square function. The difference between 20-30 is 1/3, and between 50-60 is 1/6....hmm. Never mind.........
The 5th gear quirk is partly due to the construction of the gear box. If you changed the primary ratio, you could easily build a box that was direct drive in 1st, with 5th having the most indirect energy transfer. Silly, but you could do it & keep the existing ratio's. I wonder how the 1125R's box works? & if the same rule of thumb applies?
(Message edited by aesquire on November 05, 2007) |
Buell_41
| | Posted on Monday, November 05, 2007 - 08:09 pm: |
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sorry if I'm being dense here but was this answered?
"...on an inertial dyno, if one were to do a run from stop to redline in 1st, it seems like the engine would get the dyno spinning faster... sooner... right? Would the results be skewed? What would the curves look like."} |
Blake
| | Posted on Monday, November 05, 2007 - 11:13 pm: |
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How would the dyno spin faster in 1st gear when 1st gear hit the rev limiter at around 30 mph?
The curves look much the same if engine speed is used for the X-axis. The lower gear run though would cause the engine to store the same energy (flywheel inertia times velocity) in spinning up the engine's flywheel but in a shorter amount of time, thus more power would be consumed in spinning up said flywheel thus less would transfer to the rear wheel and the dyno drum. So the lower gear runs would be slightly lower performance due to their greater inertial losses between crank and rear wheel. |
Diablobrian
| | Posted on Monday, November 05, 2007 - 11:49 pm: |
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If that doesn't work for you how about this: It's all about power loss in the transmission.
The 5th gear 1:1 is the most efficient transfer of power in the transmission.
Most times you can figure 10-15% (or maybe more!) through friction and inertia between the
crank and where the rubber meets the road. The idea is to minimize this loss and get the
truest reading you can. Otherwise it's kind of like cheating at solitaire...who are you trying
to fool? trickery with the numbers does not improve the engine's state of tune.
know what I mean? |
Tom_beckner
| | Posted on Saturday, May 24, 2008 - 03:46 pm: |
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Buell 41 writes,
"So, I like to think of torque as how hard I can slam the table with my hand (because torque is force x distance)"
False.
Torque is force applied to a lever. It's not dependent on motion or distance.
Torque is ft/lbs. For example, 550 ft/lbs, as in a lever 550 ft long with 1 lb of force applied to it, can exert 550 lbs. of force.
If the lever can raise 550 ft/lbs/sec, then it is
rated at 1 horsepower. It can raise 550 lbs, 1 ft, per second.
If the Dyno measures acceleration of the drum, or velocity in RPMs, based on the weight of the drum, it measures the horsepower in ft/lbs/sec and calculates the torque in ft/lbs that it takes to produce that result.
A dyno with a brake would be different. It would apply a force and apply the value to the torque it takes to overcome that braking force.
I could be wrong.
Tom Beckner
(Message edited by Tom Beckner on May 24, 2008) |
Bombardier
| | Posted on Saturday, May 24, 2008 - 04:13 pm: |
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Importantly,
When looking for more horsepower/torque from the mods you have done to your bike, try to emulate the exact conditions as the run before - same dyno,air temp, engine temp, grade of fuel, humidity, dyno temp etc.
This will allow you to gain the true nett result of the worth of your mod. |
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Why 5th gear