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Found some interesting potential problems with dyno results. I don’t know who this guy is but the following excerpt is from his article on Tech Page

“Other things to watch are correction factors applied for altitude, barometric pressure and temperature. These factors are NOT the same for atmo and turbo engines. Using atmo factors inflates the true, corrected HP figures on a turbo engine. In fact, look at the correction factor applied on your dyno sheets and see if they make sense. Many shady dyno operators simply enter a phantom correction factor to make the customer happy. This is a case where the dyno sheet DOES lie. Chassis dynos are essentially for tuning purposes, they are not well suited to giving an accurate hp figure.
Be aware that SAE correction factors do not apply to turbocharged engines! If your dyno sheet lists SAE corrected HP, ignore it as it is incorrect. You are better off getting an idea of where you stand by looking at observed hp with a turbo engine.”

Tech Page
 

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That's absolutely true.
People who are familiar testing and designing systems are well aware of this,
and it's unfortunate when vendors don't disclose it, but it happens all the time.
To easily visualize what's going on, take a hair dryer, put it on fan only ie. no heat, turn it on.
Place a hand over the intake or exhaust and note the rpm increase.
That's the reduction in air density going through the impeller.
The same thing happens in a turbo, as air density decreases, it takes less work by the exhaust turbine to drive the compressor at a given rpm.
So as air density decreases, the turbo rpm increases partially compensating for the density change.
Of course you're still subject to the compressor maps etc., but unlike naturally aspirated and geared superchargers which can't change their operation due to density,
the turbo has a lesser correction factor due to it's compensation capability and it's not the SAE correction dynos calculate.
 

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I'm sorry to say but you have not a clue of what you are talking about when it comes to correction factors and Dynamometer's.

SAE (Society Of Automotive Engineers) like any correction factor used on any Dynamometer is nothing more than a constant set of atmospheric conditions to correct or compare to every time you make a pull, so to create a consistency for the results received while operating the Dynamometer.
Without a correction factor there would be no way to achieve the consistency, and reliability needed to compare the results.

With the use of a correction factor, I can make a run a day or a year apart, or in say Colorado, or San Francisco and it will always provide me with the same results as if I made that Dyno run in the exact same conditions.
Assuming I am using the same vehicle and nothing has been changed or altered on that vehicle.

In other words no matter what the actual atmospheric conditions are when the Dynamometer run is performed the use of any correction factor enables you to see what the vehicle made for power as if it was always run in the same conditions. (Same Altitude, Same Ambient Air Temp and Same Humidity)

Why is this important? Because without the use of a correction factor, the results would be different every time the actual atmospheric conditions changed.
There would be NO Consistency.

Now is there a way to cheat on the results?
Sure, all you have to do is manipulate the actual conditions the vehicle is running in at the time of the Dyno run by simply increasing for example the actual air temp by making it read higher at the temp sensor.
In that case no matter what correction factor you are using (SAE, DIN, STD, EEC etc...) you will increase the correction factor and the corrected HP.

Problem with that is two fold. One the actual Hp will never change as its calculation uses no correction factor, and Two the corrected HP number that is derived by comparing the actual conditions to the corrected ones, will be abnormally high, telling you instantly that it has been falsely manipulated.

Hope this helps evaporate the mistakes of both the previous statements.

Driverxxx7
 

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I'm sorry to say but you have not a clue of what you are talking about when it comes to correction factors and Dynamometer's.

Hope this helps evaporate the ignorance of both the previous statements.

Driverxxx7


Incorrect, and it's very simple.
Turbocharged engines can compensate for density changes in a non-linear fashion since the compressor/turbine are not linearly connected to engine RPM.
The normal SAE correction is linear wrt. pressure, which is correct for naturally aspirated and supercharged engines since their intake pressure profile is linear wrt. atmospheric conditions.
Turbocharged engines have a non-linear intake density compensation wrt. atmospheric pressure, therefore the linear pressure corrections aren't accurate.
Someone who makes insults at me and others on this board isn't worth my time, so read Bell on turbocharging sometime to educate yourself.
 

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Found some interesting potential problems with dyno results. I don’t know who this guy is but the following excerpt is from his article on Tech Page

“Other things to watch are correction factors applied for altitude, barometric pressure and temperature. These factors are NOT the same for atmo and turbo engines. Using atmo factors inflates the true, corrected HP figures on a turbo engine. In fact, look at the correction factor applied on your dyno sheets and see if they make sense. Many shady dyno operators simply enter a phantom correction factor to make the customer happy. This is a case where the dyno sheet DOES lie. Chassis dynos are essentially for tuning purposes, they are not well suited to giving an accurate hp figure.
Be aware that SAE correction factors do not apply to turbocharged engines! If your dyno sheet lists SAE corrected HP, ignore it as it is incorrect. You are better off getting an idea of where you stand by looking at observed hp with a turbo engine.”

Tech Page
It won't clear up the "are turbo chargers subject to the same SAE atmospheric correction factors" arguement that seems to be brewing, but FW Little It may be worth, I do think I recall a very early version of "some" wheel dyno programs & systems that allowed the operator to insert a manual correction factor (frequently guessed at, the rough rule of tumb being @15% for single driven axle vehicles, 18 to 20% for all wheel drive) for "Drive Line Losses" This was a number, e.g. 1.25 for a "25% guestimated DLL, literally entered someplace in the recording and print out programs setup sheet. Using this, the program would automatically scale and print out the "Flywheel" guestimated power, making Owner & Tuner happy, happy if not often confused customers. Sophisticate DLL mumbojumbo artists would also throw in transverse vs. inline drive line layouts (i.e. how many times did the engine power out put have to make a 90° or 180° angle change between the flywheel and the driven wheels etc.)

On the other matter, I'm no expert, and certainly not an engineer but maybe the devils in the details? I believe both turbochargers and superchargers are affected by altitude density, its just that turbos because they are not mechanically coupled to their compression mechanism, they are not affected as much as a supercharger system is. But, that said a turbo can only be spun up just so much before the compressor wheels start trying to operate outside of their optimal efficiency range. I don't know why that property however would necessarily invalidate an SAE air density calculation going into a compressor map?
 

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Incorrect, and it's very simple.
Turbocharged engines can compensate for density changes in a non-linear fashion since the compressor/turbine are not linearly connected to engine RPM.
The normal SAE correction is linear wrt. pressure, which is correct for naturally aspirated and supercharged engines since their intake pressure profile is linear wrt. atmospheric conditions.
Turbocharged engines have a non-linear intake density compensation wrt. atmospheric pressure, therefore the linear pressure corrections aren't accurate.
Someone who makes insults at me and others on this board isn't worth my time, so read Bell on turbocharging sometime to educate yourself.
Regardless the fact still remains that you are still incorrect on your assumptions of SAE and Dynamometer's.

Now I could go into many things here to prove my point, but it would seem that it will not change what you think you know.

So let me say this

One) have you ever actually Dyno tested yourself personally, any turbo charged engines to prove your point?
Because I have tested hundreds of turbo charged engines over the years to substantiate mine.

Two), answer me this? What is the one, and only thing that will increases and decreases horsepower on an engine taking into account that AFR is a constant?

Three) It is the information that I have derived, and the subsequent intellectual property that I have created from it, over that last thirty some odd years that has provided me with the monetary rewards that supports my income, and pays for my vehicles, like my Porsche.

So i have no need to read a book someone else has written to educate myself on subjects and topics that I have both written about, and copyrighted many times before.


Driverxxx7
 

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LOL, boasting about past achievements and a quiz changing the subject?
The fact that you can't understand that a linear SAE dyno correction
is incorrect for non-linear TC output speaks for itself.
Give Corky Bell a call and argue with him that you think SAE linear dyno corrections are
valid for turbocharged engines, he'll prob. not want to waste his time either.
 

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LOL, boasting about past achievements and a quiz changing the subject?
The fact that you can't understand that a linear SAE dyno correction
is incorrect for non-linear TC output speaks for itself.
Give Corky Bell a call and argue with him that you think SAE linear dyno corrections are
valid for turbocharged engines, he'll prob. not want to waste his time either.
Thanks, Answered As expected.

Have A Nice Day!
 

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LOL, boasting about past achievements and a quiz changing the subject?
The fact that you can't understand that a linear SAE dyno correction
is incorrect for non-linear TC output speaks for itself.
Give Corky Bell a call and argue with him that you think SAE linear dyno corrections are
valid for turbocharged engines, he'll prob. not want to waste his time either.


So CPSU would I be correct understanding your position to be since SAE adjustments (temp, barometric pressure and humidity) for standardizing engine power output and measurements don't apply very well to turbocharger performance, one can't rely on any dynos, chassis or engine, for accurate, standardized power measurement on a turbo charged engine?
 

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So CPSU would I be correct understanding your position to be since SAE adjustments (temp, barometric pressure and humidity) for standardizing engine power output and measurements don't apply very well to turbocharger performance, one can't rely on any dynos, chassis or engine, for accurate, standardized power measurement on a turbo charged engine?


No, I'm not saying the J1349 SAE correction isn't useful for turbocharged engines, it's very useful, but you have to be aware of the potential error.
As you increase DA (density altitude) being read, by dynamometer atmospheric measurements on a turbocharged
engine being tested, there is an error incorporated proportional to the DA being read while using only J1349 for correction.
There was an SAE paper that discussed the additional factors DOI: 10.4271/690309 "Correction of Turbocharged Engine Performance to Standard Conditions and Prediction of Nonstandard Day Performance"
based on aircraft. There are also a number of SAE papers showing more research into the differences when correcting for turbocharged diesel engines (because of the near-universal use of turbochargers in trucking)

For example, there was a shop well known for turbocharged cars that was located at 6000ft MSL.
One of their kits consistently yielded ~250 rwhp SAE corrected. When those cars were brought to sea level and retested with exactly the same AFR/Temps/fuel etc., they produced ~5-7% less power than expected.
Conveniently, the same shop produced supercharged kits with similar power, on the same engine management, fuel etc., and showed approx. the same SAE corrected power at 6000 DA as 0 DA as you would theoretically expect.
Now, am I claiming that there is a 1% SAE J1349 error/1000ft DA on turbocharged cars? No, like you mentioned, where the compressor is on it's efficiency map
is going to affect the mass flow headroom available for a given setup along with intercooler/exhaust efficiency etc. etc.,......
my point is just that there is an error there, and it makes it easier for less than honest shops to manipulate the "SAE" numbers by introducing incorrect atmospheric conditions.
They could do that with any engine, NA, SC or TC, but with a turbocharged engine the effect is greater due to this additional error.
That's why it's wise to be skeptical of dyno charts that don't show the correction and atmospheric conditions used and why I cringe when it happens on turbocharged cars.
Likewise, if the DA/correction is near 0, this error is a non-issue and another reason those factors have to be clearly and accurately stated with the testing.
 
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