Dyna-pack dynos- what everyone should know!
11-15-2008, 11:03 PM
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Dyna-pack dynos- what everyone should know!
I have seen this happing more and more over the forums, and many are claiming that the Dyna-pack Hub dyno's read higher than any other type. Some claim that they are reading flywheel horsepower, others say they just read higher due to having no wheels to measure. On our dyna-packs they read consistently 6-9% lower than a dyno-jet. And very very near the same as a mustang dyno. HOWEVER, this is when properly setup, and the dyno operator is honest with the details. Read further and I will explain.
Readings and results--
Its pretty easy to spot fake inflated dyna-pack dyno charts, but only if the person posting it will show the sidebar with the specs. If its just a chart, I really never buy it, but there still may be a few things to look for. Here is why. A dyna pack can show actual rear wheel horsepower and torque........ OR ESTIMATED flywheel horsepower! The estimated horsepower is a percentage the DYNO OPERATOR punches in!! It can be 2% or even over 50%!! This is the beginning of where things go south. And the reason for the huge misunderstandings. I will show you how to spot one of these below.
A proper chart--
Okay first of all here is a complete trustworthy dyno chart. Why? You will notice it shows the sidebar of information. If you have this sidebar, its near impossible to hide inflated numbers.
So you want the sidebar, and make sure its SAE correction. This makes a car in hot or cold, high altitude or low altitude even with each other. I circled both things to look for in red.
Now that we have that, here is what everything should look like. Now notice in the sidebar it will say "axle power" and just "power". If no additional corrections have been added, then both will be exactly the same.
Here is another dyno chart with corrections for "power". Notice I circled them both and they are different. In this case it was 10% correction. This dyno chart can easily made into a inflated one. I still have selected "axle power" however to show on the graph. SO that means in this case the horsepower is accurate. I could easily select "power" and the graph will then be fake.
Now this is a bit complex to explain, but dyna-packs read actual rear wheel torque. Which means the number is going to be WAY higher than anyone is used to. Why? Gear reductions. Now every other dyno will display flywheel torque, with drivetrain losses. Dyna-pack will too, but only without corrections. Here is how to double check. I circled this cars actual rear wheel torque. Which is 1051 rwtq. If you take that number and divide by its gear ratio (4.10:1) you will get flywheel torque with drivetrain loses. Do the math, and you get 257rwtq like we are all used to seeing. If you check the faulty chart however, you will see in the side bar under "Torque" it says 270. That is again the 10% correction being applied. And the torque line is a false inflated one!
Now finally, if no sidebar is presented, there is a few more things to help a bit when checking it.
First see if the torque and horsepower are scaled the same left and right. If so, the torque and horsepower should cross at 5252.
Once that is established, the only thing left to maybe save the chart is make sure it says "axle power" somewhere in the chart. As I circled in red. If it just says "torque" and "power", I WOULD BE SKEPTICAL. As the dyno user could have entered anything. Maybe 10-15% for showing the estimate flywheel power and torque, or even just 5% to show a bit of an edge over everyone else.
I know this was a long post, but I hope maybe it laid out the issues, and helps a few distinguish between real and fake dyna-pack charts.
Readings and results--
Its pretty easy to spot fake inflated dyna-pack dyno charts, but only if the person posting it will show the sidebar with the specs. If its just a chart, I really never buy it, but there still may be a few things to look for. Here is why. A dyna pack can show actual rear wheel horsepower and torque........ OR ESTIMATED flywheel horsepower! The estimated horsepower is a percentage the DYNO OPERATOR punches in!! It can be 2% or even over 50%!! This is the beginning of where things go south. And the reason for the huge misunderstandings. I will show you how to spot one of these below.
A proper chart--
Okay first of all here is a complete trustworthy dyno chart. Why? You will notice it shows the sidebar of information. If you have this sidebar, its near impossible to hide inflated numbers.
So you want the sidebar, and make sure its SAE correction. This makes a car in hot or cold, high altitude or low altitude even with each other. I circled both things to look for in red.
Now that we have that, here is what everything should look like. Now notice in the sidebar it will say "axle power" and just "power". If no additional corrections have been added, then both will be exactly the same.
Here is another dyno chart with corrections for "power". Notice I circled them both and they are different. In this case it was 10% correction. This dyno chart can easily made into a inflated one. I still have selected "axle power" however to show on the graph. SO that means in this case the horsepower is accurate. I could easily select "power" and the graph will then be fake.
Now this is a bit complex to explain, but dyna-packs read actual rear wheel torque. Which means the number is going to be WAY higher than anyone is used to. Why? Gear reductions. Now every other dyno will display flywheel torque, with drivetrain losses. Dyna-pack will too, but only without corrections. Here is how to double check. I circled this cars actual rear wheel torque. Which is 1051 rwtq. If you take that number and divide by its gear ratio (4.10:1) you will get flywheel torque with drivetrain loses. Do the math, and you get 257rwtq like we are all used to seeing. If you check the faulty chart however, you will see in the side bar under "Torque" it says 270. That is again the 10% correction being applied. And the torque line is a false inflated one!
Now finally, if no sidebar is presented, there is a few more things to help a bit when checking it.
First see if the torque and horsepower are scaled the same left and right. If so, the torque and horsepower should cross at 5252.
Once that is established, the only thing left to maybe save the chart is make sure it says "axle power" somewhere in the chart. As I circled in red. If it just says "torque" and "power", I WOULD BE SKEPTICAL. As the dyno user could have entered anything. Maybe 10-15% for showing the estimate flywheel power and torque, or even just 5% to show a bit of an edge over everyone else.
I know this was a long post, but I hope maybe it laid out the issues, and helps a few distinguish between real and fake dyna-pack charts.
11-16-2008, 02:51 AM
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nice to know 
but, anyway..it not about the 'amount of torque/hp' usually right? its the offset from the baseline dyno. unless we're comparing hp between cars.....in which case its a dck waving contest....lol
but, anyway..it not about the 'amount of torque/hp' usually right? its the offset from the baseline dyno. unless we're comparing hp between cars.....in which case its a dck waving contest....lol
11-17-2008, 04:18 AM
#4
A few years back I suggested we all just use the ratio of current dyno over the baseline dyno.
An example would be a boosted S with an original baseline of 200 rwhp now putting out 300 rwhp would have a ratio of 1.5. If the output was 400 rwhp the ratio would be 2.0.
It eliminates many of the differences discussed here.
Unfortunately many owners don't have a proper baseline to start with. My engine has never been run without the supercharger so I don't have a baseline. Other S owners changed dynos or dyno types.
Just to clear the air, a factor not mentioned here is the dynos can be calibrated when they are set up pushing the results up or down. This results in DynaPacks that read differently. The op's dyno probably reads a fair amount lower than Church's dyno due to the initial calibration.
An example would be a boosted S with an original baseline of 200 rwhp now putting out 300 rwhp would have a ratio of 1.5. If the output was 400 rwhp the ratio would be 2.0.
It eliminates many of the differences discussed here.
Unfortunately many owners don't have a proper baseline to start with. My engine has never been run without the supercharger so I don't have a baseline. Other S owners changed dynos or dyno types.
Just to clear the air, a factor not mentioned here is the dynos can be calibrated when they are set up pushing the results up or down. This results in DynaPacks that read differently. The op's dyno probably reads a fair amount lower than Church's dyno due to the initial calibration.
11-17-2008, 03:29 PM
#6
Former Moderator
Church's dyno reads high. Partly due to a calibration issue, which I understand came when the dyno was damaged during a shop move. I'm not sure what kind of correction factor Sean may use. I don't think I've seen one of his dyno charts showing the data shown in the OPs charts.
01-30-2009, 09:43 AM
#7
Registered User
Sorry to bring this back up, but it was just brought to my attention.
1) Our dyno reads exactly the same today as it did 7 years ago when we first bought it. I tested my S2000 on it (stock AP1) the day it arrived and it made 212-213 hp vs. 200-201 on my local Dynojet. There are no correction factors used.
2) The easy way to tell whether anyone is fudging numbers is to use the preformatted screens rather than the comparison window shown. The preformatted screens for "flywheel" (on the older software) power/torque include a box at the bottom for TCF which stands for Transmission Correction Factor. As long as that value is 1.0, what you see on the plot is what was measured at the hubs. We never use the comparison screen as shown because it tends to confuse people as well as be open for manipulation.
3) A Dynapack should always read higher than a roller dyno. Physics dictates it. If you don't believe that, then you must believe that roller dynos are inflated. Considering that in inertia mode, Mustang, Dynojet and Superflow have all been shown to be within 1%, this is unlikely. The cause for higher readings comes down to driveline loss reductions, primarily in wheel/tire inertia and in rolling resistance elimination. See SAE Paper #2002-01-0887 You'll have to pay to download it, but the testing data is outstanding. You'll see that rolling resistance losses alone on a roller dyno can be quite large. In the test case, it was shown that for a 245/50/17 tire the losses were 16 hp at 110 mph. This is a loss that will not be present on a Dynapack. Something to think about
UL
1) Our dyno reads exactly the same today as it did 7 years ago when we first bought it. I tested my S2000 on it (stock AP1) the day it arrived and it made 212-213 hp vs. 200-201 on my local Dynojet. There are no correction factors used.
2) The easy way to tell whether anyone is fudging numbers is to use the preformatted screens rather than the comparison window shown. The preformatted screens for "flywheel" (on the older software) power/torque include a box at the bottom for TCF which stands for Transmission Correction Factor. As long as that value is 1.0, what you see on the plot is what was measured at the hubs. We never use the comparison screen as shown because it tends to confuse people as well as be open for manipulation.
3) A Dynapack should always read higher than a roller dyno. Physics dictates it. If you don't believe that, then you must believe that roller dynos are inflated. Considering that in inertia mode, Mustang, Dynojet and Superflow have all been shown to be within 1%, this is unlikely. The cause for higher readings comes down to driveline loss reductions, primarily in wheel/tire inertia and in rolling resistance elimination. See SAE Paper #2002-01-0887 You'll have to pay to download it, but the testing data is outstanding. You'll see that rolling resistance losses alone on a roller dyno can be quite large. In the test case, it was shown that for a 245/50/17 tire the losses were 16 hp at 110 mph. This is a loss that will not be present on a Dynapack. Something to think about
UL
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