Competition Engine dyno vs Chassis dyno

[JLackman]

I'm on a roll now...



Reference; New Dyno Numbers 1020 H. p page 2



To start the discussion;



Correction standards should work the same way on both engine dynos and chassis dynos. If you don't agree, please explain.



Would anyone explain in detail how chassis dyno DAQs handle weather inputs and the SAE corrections?



What SAE correction standards are used? J607? J1349?



Since engine inlet air is the parameter most likely to change during a dyno pull how is the engine inlet air temperature measured and input into a chassis dyno DAQ?

 

[Diesel Freak]

This should be good!!!



Correction standards "would" be applicable between Chassis and Engine dyno's "IF" the same parameters were monitored. You and I both know that this is not the case. Shoot, I had to hook up a fluke Multimeter just to get post charge air cooler temp in order to see just how close calculated density ratio was to actual because the dyno was unable to gather this info.



FYI, you will not be able to tell anyine here anything they don't already know!!! and if you try, all you will do is :-{}



Just admit that Diesel (lack of) Performance is completely hilljack, and stick to what you know... . Trying to educate a Hilljack is a complete waste of time (been there done that).



However, I would love to read what you want to share with us!!!!



Most Diesel Shops cant even comprehend the info on compressor map.







now where is that little Popcorn eating Smiley?

 

[JLackman]

I think it is pretty clear the intent of correcting dyno brake numbers to a known standard is so that they can be compared in a meaningful way to other dyno brake numbers corrected to the same standard. This is why it is important to know what the correction standard in use is. J1349 will result in corrected brake numbers about 4% lower than J607. J 607 is more commonly used.



SAE J 607 standard specifies 29. 92" absolute barometric pressure, 60F inlet air temperature, and 0% humidity. On my dyno the actual absolute barometric pressure and humidity is input to the DAQ before the dyno test. The DAQ has a real time inlet air temperature input as this is the one of the three most likely to change during a pull. The DAQ calculates and applies the correction factor to the brake numbers (brake torque and brake horsepower) on the fly during a pull.



If the actual air conditions were 29. 92", 60F, and 0% humitidy the brake numbers would be exactly the same as the corrected numbers.

 

[Diesel Freak]

Keep in mind that most Chassis dyno owners do not know what standard they are using. They just establish a baseline on their dyno, and tune with respect to it..... which by the way is why people see such a HUGE difference in indicated power from one dyno to the next.

 

[JLackman]

What I am interested in is exactly how weather conditions are input to a chassis dyno DAQ.



The parameters specificed by SAE J 607 are humidity, absolute barometric pressure and engine inlet air temperature. Doesn't matter if the dyno is a chassis dyno or an engine dyno.



SAE J1349 gets more complicated as there is a special section for CI boosted engines but I have a hunch chassis dyno DAQs do not bother with that part of 1349 at all. I know most engine dyno DAQs don't. If they did there would be some inputs beyond the basic three, humidity, absolute barometric pressure, and inlet air temperature.



Has anyone heard of any additional inputs? If so what are they?



Here is a pretty technical discussion that gets into this a bit;



Dyno corrections at high altitude and with boosted engines

 

[JLackman]

Keep in mind that most Chassis dyno owners do not know what standard they are using. They just establish a baseline on their dyno, and tune with respect to it..... which by the way is why people see such a HUGE difference in indicated power from one dyno to the next.

Why in the world wouldn't they know what standard they are using???



Well I think the same might be true of many engine dyno operators.



There is no excuse for not knowing.

 

[Diesel Freak]

Here is a pretty technical discussion that gets into this a bit;



Dyno corrections at high altitude and with boosted engines

That's a good read!!!

 

[Diesel Freak]

Why in the world wouldn't they know what standard they are using???



Well I think the same might be true of many engine dyno operators.



There is no excuse for not knowing.

I hear ya!!

 

[Diesel Freak]

Here is an off topic question for ya.



What do you think of the pseudo motorsport of Dyno Days? :-laf

 

[Amish Elegance]

FYI, you will not be able to tell anyine here anything they don't already know!!! and if you try, all you will do is :-{}



Just admit that Diesel (lack of) Performance is completely hilljack, and stick to what you know... . Trying to educate a Hilljack is a complete waste of time (been there done that).

Usually the :-{} starts after someone exhibits a pompous attitude like illustrated above. We "hilljacks" do not like to be patronized.



Thanks for starting this thread.



I have no arguments in relation to the statement that engine dyno's are superior to chassis dynos in many ways. I don't think you'll find anyone on this board that'll argue that statement. (open mouth in preparation for foot) In a controlled environment you can measure with far greater accuracy and repeatability than in an engine bay or on any chassis dyno. Period.



Dont sell the chassis dyno guys short though... You can learn alot there too. Dunbar can tell you alot about your engine while you're on his dyno. How is it gonna spool. What kinda driveability issues you may have. How you can get more out of your engine. From his dyno, he can even predict, with great accuracy, what you're gonna trap in the 1/4. (things that "hilljacks" care about) Some of these things, you cant measure with decimals, and yeah its not as scientifically founded as the data you'd get from several hundred sensors. But tuning on a chassis dyno will make your truck faster. Thats all most of us care about.



Your fees, however, are a lower than I would have thought for an engine dyno. Thats another aspect... Cost. More importantly the cost/benefit of the two. You can get a few pulls on a chassis dyno for around $70. Your fees, though seemingly reasonable, were quite a bit higher.

 

[Diesel Freak]

Usually the :-{} starts after someone exhibits a pompous attitude like illustrated above. We "hilljacks" do not like to be patronized.

What is worse... is when a West Coast Redneck does the Patronising!!! :-laf

 

[JLackman]

Here is an off topic question for ya.



What do you think of the pseudo motorsport of Dyno Days? :-laf

I don't know anything about Dyno Days, I should read up on it.



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The amazing part of this was we did this on a 600 RPM per second acceleration rate.

Does anyone understand what this means?



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Related question; How do chassis dynos deal with driveline inertia effects?



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I'm not intending to "sell chassis dyno guys short", any dyno is a great tuning tool, I'm just curious about the methodology, especially when there is such an obvious my hp is bigger than your hp attitude around here.

 

[KLockliear]

The Dynojet chassis dyno (which is what we use) has several built-in correction factors. We only use the SAE correction factor at our shop. It is the SAE J1349, Revision June 1990 to be exact.



The dyno hardware (Dynoware EX+) automatically samples atmospheric pressure, temperature and relative humidity. It does not have an input to read boost pressure.

 

[JLackman]

The Dynojet chassis dyno (which is what we use) has several built-in correction factors. We only use the SAE correction factor at our shop. It is the SAE J1349, Revision June 1990 to be exact.



The dyno hardware (Dynoware EX+) automatically samples atmospheric pressure, temperature and relative humidity. It does not have an input to read boost pressure.

Thanks.



So how do your corrected numbers compare to other chassis dynos?

 

[COMP461]

I have all ways taken dyno numbers as nothing more then tuning aids, it doesn’t mater if the dyno read in abc or xyz , it must be repeatable. I you use any kind of dyno, you first must make you test parameters such that the numbers will repeat themselves if you change nothing. How many times have you seen a chassis dyno session where the guy keeps beating the same combination in order to get a higher number , this is somewhat ruled out with a experienced dyno operator, but it’s a variable that is very volatile in that the method’s are so spermatic. On an engine dyno it’s the exact same every time. You control the water temp, the oil temp the air temp is monitored, and when you pull its at the same rate ever time.

Now to the reason to dyno, a lot of people dyno for numbers to brag about , but the best reason is to develop a engine program, in my session the other night I had a 4 hour block of time to use , and a green motor, I could have stair stepped this motor and steady state pulled it , and printed a much larger number , or even posted the observed number which was in the 1160 range , but I did test to learn , heck the motor only had 25 degrees of timing . the parameters of this project was to make enough power to run solidly in the sevens with a diesel truck and this is more then enough power to achieve this. Like David’s dyno, he can predict ET from his numbers, I can also,

 

[RustyJC]

The amazing part of this was we did this on a 600 RPM per second acceleration rate.

Does anyone understand what this means?

The engine RPM was increasing at a rate of 600 RPM per second.



Rusty

 

[JLackman]

The Dynojet chassis dyno (which is what we use) has several built-in correction factors. We only use the SAE correction factor at our shop. It is the SAE J1349, Revision June 1990 to be exact.



The dyno hardware (Dynoware EX+) automatically samples atmospheric pressure, temperature and relative humidity. It does not have an input to read boost pressure.

Another question, do you do upsweep, downsweep or steady state testing?

 

[JLackman]

The engine RPM was increasing at a rate of 600 RPM per second.



Rusty

How would the brake and corrected numbers from an upsweep compare to a downsweep and to a steady state test?



People just thow out chassis dyno numbers, everybody cobbs on compares with no questions asked, COMP states the actual sweep rate used and just gets made fun of.



Weird.



Sweep testing has an effect on both uncorrected and corrected numbers, when the rpm is changing the engine (+ driveline in the case of a chassis dyno) is either giving up inertia (down sweep) thus increasing brake and corrected numbers over steady state numbers or expending power accelerating (upsweep) thus decreasing brake and corrected numbers over steady state numbers.



If dyno numbers are going to be compared one must know the method behind the numbers to objectively compare them.

 

[GIT-R-DONE]

Maybe some weekend we could have an engine dyno day at your shop, how many trucks do you believe we could do in a weekend? It would be impractical to have one..... agree ?



Most people here want to know what they are putting to the ground.



I am sure that there are many things that you can tell with an engine dyno, but it is not practical for us "HillJacks" that arent after the elusive 6 second 1/4 mile truck. Yes, in reference to COMP, there are many things I am sure he has tried and still has a ways to go. Congrats to him for his effort. Although there are many things I dont like about his attitude, he is there pushing the envelope..... and that is what is needed in the Diesel world.



He just cant forget..... he isn't the only one doing it. There are many others out there doing the same thing, they just dont talk about it.

 

[JLackman]

That is not the point.



The point is what is behind the numbers. Don't you care if the dyno numbers are accurate and meaningful or not?



All the things I bring up here, sweep rates, inertia, correction standards can have a huge affect on dyno numbers, yet people here directly compare COMPs 1128 on a SF-901 to the 1050 on a chassis dyno without any questions about what is behind the numbers and how the testing was done.



If chassis dynos are for entertainment only, well, let r rip then, but don't pick on someone who wants to be a bit more scientific about it.