Dynamometer Types and Number Validity

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Charles

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I have heard it said more than once that load cell dynamometers offer "real world" numbers and that the classic Dynojet 248c produces inflated, non-realistic numbers.

Okay, fine. While I don't see evidence that supports that, for the moment lets just assume that to be a fact. And not waste any time at all arguing about it.



There are two basic concepts that define the validity for any given tool of measure, and lets start with the understanding that a dynamometer is just that. A tool used for measuring engine or vehicle output. These two concepts are Precision and Accuracy. Between the two of them you can begin to build validity for any given measuring tool.

When you hear someone talking about the numbers being "real world" or "correct" on one machine vs another, they are referring to the Accuracy of the device. How closely does the value returned by the device match the actual output being developed. That is Accuracy.

When you hear someone talking about getting wildly varying results from one session to another, or even from one pull to the next, that is directly related to the Precision of the unit. Precision is the level to which you can expect to receive the same value returned when nothing has changed. Just as you would expect a micrometer to return the same value (within an acceptable range) no matter how many times you measured the thickness of a piece of tubing for instance. If you measured 3.012" one time, and you placed the mic right back on the same spot (as best the human eye can tell) you would expect to get something like 3.015 or 3.011, 3.018, so on and so forth. However, if after the mic returned a value of 3.012 on the first test you then retested twice more and got 2.34 and 5.76 respectively, you would probably throw it in the trash can and go get a decent micrometer. I know I would.


Here's the point. Step one is precision. First and foremost, the device MUST produce consistent, reliable numbers each and EVERY time you use it. THEN.... and ONLY then, does it matter the degree to which those numbers align themselves with the actual value.

In other words, you cannot very well argue the validity of one dynamometer over a Dynojet 248c on the basis of Accuracy, when it can't even produce the pre-requisite level of Precision needed to even QUALIFY for a debate on Accuracy...

60+hp swings are just shrugged off with load cells. Just mood swings I guess.

Whereas you can dyno your truck on a Dynojet 248c and the uncorrected values will be spot on, no matter which unit you use anywhere on planet earth, any day, any time.



Is the Dynojet Accurate? I don't know. The trap speed/Et calculators sure think so, but I don't know. But it is damn sure Precise. And you can't very well tackle accuracy before precision, unless you enjoy putting the cart before the horse.

If the load cell values are so accurate and so "real-world", fine. But let me ask you this. Which one? Which number is the "right" one? The last pull? Or the one from 3 hours ago? Or the one from yesterday? Or the one from last week? None of which are even remotely the same, and 30 to 100 or so hp apart?

Clearly you cannot have the "right" number, when you don't even have A number in the first place.


:1tooth:
 
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Charles said:
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Whereas you can dyno your truck on a Dynojet 248c and the uncorrected values will be spot on, no matter which unit you use anywhere on planet earth, any day, any time.


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Ummm, the uncorrected numbers WILL vary from place to place, even from morning to noon to evening on a dynojet if you go by un-corrected. If you said corrected, then the number, in theory, should be the same.
 
JasonCzerak said:
Ummm, the uncorrected numbers WILL vary from place to place, even from morning to noon to evening on a dynojet if you go by un-corrected. If you said corrected, then the number, in theory, should be the same.
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Sorry. I wasn't talking about "theory", I was talking reality. In Reality uncorrected Dynojet 248c numbers are comparable across the planet.

Correction factors should be filed in the same place as load cell dyno sheets. Under the worthless crap heading.

:1tooth:
 
Charles said:
Sorry. I wasn't talking about "theory", I was talking reality. In Reality uncorrected Dynojet 248c numbers are comparable across the planet.

Correction factors should be filed in the same place as load cell dyno sheets. Under the worthless crap heading.

:1tooth:
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So you are telling me, that if I have said dynojet 248c in Miami Florida and it dyno'ss 200hp at sea level, 60 degrees 30% humidity (hypothetical, I'm sure it's more humid...) that if the same vehicle and dyno were to travel to Denver, in 95 degree heat at 6000foot with 100% humidy, so it's freaking raining out side, it will still dyno 200hp un-corrected?

If so, prove that.
 
Now, I can very well see differences in calibration between different dyno of the same time.. many factors in that one. mainly maintenance of it. you are re-greasing it and use a different grease in the barrings, that would effect numbers. Or in my case last dyno event, the brakes on the drum were acting up.
 
JasonCzerak said:
So you are telling me, that if I have said dynojet 248c in Miami Florida and it dyno'ss 200hp at sea level, 60 degrees 30% humidity (hypothetical, I'm sure it's more humid...) that if the same vehicle and dyno were to travel to Denver, in 95 degree heat at 6000foot with 100% humidy, so it's freaking raining out side, it will still dyno 200hp un-corrected?

If so, prove that.
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You understand that Uncorrected numbers are Actual horsepower right? That's why it reads ACTUAL instead of SAE on an uncorrected graph.

Or do you like it better when someone can take a truck and dyno 240rwhp corrected in Ft Walton Beach Florida, and then go dyno 380rwhp corrected in Ft. Collins Colorado with the same truck?


:1tooth:
 
Charles said:
You understand that Uncorrected numbers are Actual horsepower right? That's why it reads ACTUAL instead of SAE on an uncorrected graph.

Or do you like it better when someone can take a truck and dyno 240rwhp corrected in Ft Walton Beach Florida, and then go dyno 380rwhp corrected in Ft. Collins Colorado with the same truck?


:1tooth:
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Do you not have it backwards there?

uncorrected as I understand is actual hp for the conditions. When the conditions change, the actual will go up or down depending on the change in location.

If you dyno at see level you will dyno higher then if you would in Denver over 5000 feet. That is uncorrected.

Corrected Power
 
IMHO, if you are going to compare trucks across the country and though out the year to see who has the most HP, it has to be CORRECTED numbers.

Otherwise, it's hear say.
 
JasonCzerak said:
IMHO, if you are going to compare trucks across the country and though out the year to see who has the most HP, it has to be CORRECTED numbers.

Otherwise, it's hear say.
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And you're opinion would be wrong, as we aren't driving naturally aspirated gassers here.

Sure elevation, temperature and humidity effect power output. But not remotely to the level that dynamometer correction software shows.

And if you'll think about it, it's rather simple. Uncorrected numbers are literally the ACTUAL output the engine/vehicle produced right then and there (to whatever level of accuracy the dynamometer in use can achieve). Corrected numbers are NEVER the actual output unless you happen to be making pulls at STP. Otherwise, they are purposefully, and knowingly incorrect. They are quite literally not the actual output, by definition.

It's like watching someone in a boat, driving in a no wake zone that's constantly cutting the wheel back and forth trying to keep the boat from drifting each way, and ending up making things far worse and far less accurate than if they had just put their hand back on their beer, and let the damn thing go. 9 times out of 10 the boat ends up traveling far smoother and straighter than with all their effort to constantly "correct" it's movement each way. Such as is the case with the negative correction in Florida and positive correction in Colorado, instead of just leaving it alone.

I'm gonna stick to uncorrected Dynojet 248 numbers, because they're consistent as hell. You do what you like.
 
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Here in CA, the uncorrected numbers are often higher. Dynos are tuning tools. DC performance down the street has a dynojet, and a dynapak load dyno for tuning. They said the dynapak is about 7% higher. Other load dynos seem a little lower than the dynojet, which if memory serves was based upon the stock horsepower of a Yamaha V-max motorcycle or something. They're just numbers, and as long as they're not way off, all are pretty legit. The only way to know for sure is to run on multiple dynos, or run on one that is proven to be fairly accurate compared to trap speed calculators.

All of that being said, I know there can be a bunch of number fudging when it comes to dynoing. We have a dyno here in Los Angeles that will usually read about 10% higher than anywhere else.

Two more cents--correcting a run on a truck with twins and two stages of nitrous is crazy, the air is easily as oxygen rich as it ever was at sea level with that kind of boost and nitrous.
 
Charles said:
And you're opinion would be wrong, as we aren't driving naturally aspirated gassers here.

Sure elevation, temperature and humidity effect power output. But not remotely to the level that dynamometer correction software shows.

And if you'll think about it, it's rather simple. Uncorrected numbers are literally the ACTUAL output the engine/vehicle produced right then and there (to whatever level of accuracy the dynamometer in use can achieve). Corrected numbers are NEVER the actual output unless you happen to be making pulls at STP. Otherwise, they are purposefully, and knowingly incorrect. They are quite literally not the actual output, by definition.

It's like watching someone in a boat, driving in a no wake zone that's constantly cutting the wheel back and forth trying to keep the boat from drifting each way, and ending up making things far worse and far less accurate than if they had just put their hand back on their beer, and let the damn thing go. 9 times out of 10 the boat ends up traveling far smoother and straighter than with all their effort to constantly "correct" it's movement each way. Such as is the case with the negative correction in Florida and positive correction in Colorado, instead of just leaving it alone.
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Who here reading this has dynoed and has uncorrected numbers from 2 extream environments?

i know for a fact my truck clears up the smoke better when it's -32 out then when it's 100 degrees out. and I've been in both extreams in the exact same spot on the exact same road doing the exact same thing, going well over the speed limit..

I suppose I'll have to dyno closer to summer when it's 90 out, and ensure it's 90 in the dyno cell on a dynojet 248h and then get a small session in the dead of winter. Same altitude, 2 different extreams in temp and humidity, same dyno.

Donations will be welcome, once I get my current setup dialed in, I don't plan on changing anything unless something breaks.

I appears to me that turbo charged motors are effected the same as N/A, maybe to a lesser extent, but oxygen content is still the same.

I suppose one good way to find out is turbine shaft speed. Does it spin faster in the summer vs winter?
 
JQmile said:
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All of that being said, I know there can be a bunch of number fudging when it comes to dynoing. We have a dyno here in Los Angeles that will usually read about 10% higher than anywhere else.

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I think that's the biggest problem of them all right there. :) Like i said earlier, maybe they use a different grease in the rollers to change the "known acceleration rate of X weight"
 
I for one agree with everything he said..

EVERY SINGLE time I've put a DynoJet (Dunbars) numbers to the test on a the track, they are dang near the same.....plus / minus for temps, humidity, etc....

I'm chasing a power loss issue right now....Trucks acting weird after I broke my input shaft....I thought I might still have a tranny issue....went to the track and ran some times.....Just got off of Dunbars dyno yesterday at his house.....The dam truck laid down the same freakin numbers I hand calculated from trap speeds and weight...So I have a power issue, not tranny...

Dyno Jet (Dunbars) is the ONLY way to fly!!!!!!!
 
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There was an article we did on that in Diesel Power a while back based upon an SAE study that was done on big rig trucks. Basically, as long as the turbo is able to maintain it's pressure ratio by spinning faster at high altitudes, the correction factor is halved per every 15 psi of boost that the engine sees. So if N/A correction is 1.10, a 15psi boosted motor would only be 1.05, 30psi 1.025, etc.
 
How often and/or what is used to calibrate a dyno? I've seen CAT scales that weigh big trucks calibrated for accuracy, but never heard of anyone doing this for engine or chassis dynos. Thanks, love the site, Neil
 
JasonCzerak said:
Who here reading this has dynoed and has uncorrected numbers from 2 extream environments?

i know for a fact my truck clears up the smoke better when it's -32 out then when it's 100 degrees out. and I've been in both extreams in the exact same spot on the exact same road doing the exact same thing, going well over the speed limit..

I suppose I'll have to dyno closer to summer when it's 90 out, and ensure it's 90 in the dyno cell on a dynojet 248h and then get a small session in the dead of winter. Same altitude, 2 different extreams in temp and humidity, same dyno.

Donations will be welcome, once I get my current setup dialed in, I don't plan on changing anything unless something breaks.

I appears to me that turbo charged motors are effected the same as N/A, maybe to a lesser extent, but oxygen content is still the same.

I suppose one good way to find out is turbine shaft speed. Does it spin faster in the summer vs winter?
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Turbocharger

History

The turbocharger was invented by Swiss engineer Alfred Büchi. His patent for a turbo charger was applied for use in 1905.[1] Diesel ships and locomotives with turbochargers began appearing in the 1920s.

Aviation

During the First World War French engineer Auguste Rateau[2] fitted turbo chargers to Renault engines powering various French fighters with some success.[3]

In 1918, General Electric engineer Sanford Moss attached a turbo to a V12 Liberty aircraft engine. The engine was tested at Pikes Peak in Colorado at 14,000 feet (4,300 m) to demonstrate that it could eliminate the power losses usually experienced in internal combustion engines as a result of reduced air pressure and density at high altitude.[4]

Turbochargers were first used in production aircraft engines in the 1930s before World War II. The primary purpose behind most aircraft-based applications was to increase the altitude at which the airplane can fly, by compensating for the lower atmospheric pressure present at high altitude. Aircraft such as the P-38 Lightning, B-17 Flying Fortress, and P-47 Thunderbolt all used turbochargers to increase high altitude engine power.
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That's all good, assuming your not spinning the charger outa it's map! :)

Well, I'm using logic here based on what I know so far about turbos, this is where my turbo knownled starts to get fuzzy.

However, If you are already at the top of said chargers efficiently for shaft RPM at sea level to make ends meat, it's not going to do very good at 14,000 feet, correct?

Or does all that efficiently and shaft rpm stuff change linearly with altitude and other weather conditions.
 
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