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New dyno power drops way off

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(@philstubbs)
Posts: 16
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Topic starter
 

This is a new dyno I am getting working. Calibrated the load cell, set MOI, set gear ratio for the vehicle, everything. When the run starts the power seems to be accurate but as the run goes it just drops off to almost nothing. Water pressure in the brake looks good and the engine follows the 500 rpm/second perfectly so I think it’s loading as it should. The graph just looks upside down though. 

 
Posted : 05/09/2024 2:12 am
(@philstubbs)
Posts: 16
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Topic starter
 

something else I noticed after posting this. I don’t know how but I found m my roller circumference set to 7 meters when it should be 0.638 meters. I’d imagine that is contributing to this. 

 
Posted : 05/09/2024 3:49 am
(@admin)
Posts: 1447
Member Admin
 

Hi,

The roller circumference only affects Speed and Distance. 

Your load cell is likely calibrated the wrong way or the MOI is set wrongly. Check the Load cell torque channel (it should be positive). Also check the Wheel power/Torque to see that it is not the retardation measurement that is wrong. 

Post the csv file if you are stuck

 

 
Posted : 05/09/2024 8:52 am
(@philstubbs)
Posts: 16
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Topic starter
 

Here is the file from the last run.

 
Posted : 05/09/2024 5:36 pm
(@admin)
Posts: 1447
Member Admin
 

Hi,

A few things here.

  1. It looks like you run a low gear. The roller RPM (RPM1) is maximum just 350 RPM. Generally use the highest gear you can, while still being under the RPM limit of the dyno
  2. The brake is at 100% for a long time, meaning it is out of capacity. Using a higher gear helps this too
  3. Looks like the data compression is on. Turn it off, this is just used for very long runs (hours)

Fix that first, then we can look at the MOI. The Load cell is calibrated the correct way.

 
Posted : 05/09/2024 6:46 pm
(@philstubbs)
Posts: 16
Member
Topic starter
 

It's odd that it never has done that before, but talking to Kevin Hamilton he gave me an idea of what I need and what I am currently using is nowhere near enough. 

What do you think of this pump? Turns out I had it in storage already and didn't realize it seems to fit the needs perfectly. 

 

https://www.grainger.com/product/1N439?gucid=N:N:PS:Paid:GGL:CSM-2295:4P7A1P:20501231&gad_source=1&gclid=CjwKCAjwreW2BhBhEiwAavLwfCB4UIkZN9DT9QsHnXeV6tdYfQkCBLPnjDoB6oJu0MRHADINmPdFyxoC198QAvD_BwE&gclsrc=aw.ds

 
Posted : 05/09/2024 9:42 pm
(@admin)
Posts: 1447
Member Admin
 

That is a better pump, so you can try that. 

But user higher gear in any case.

 
Posted : 06/09/2024 12:47 pm
(@philstubbs)
Posts: 16
Member
Topic starter
 

I’m using the 1:1 gear in the transmission. According to Kevin Hamilton it wouldn’t be safe to get these rollers over 120 mph. With the cars I am working with that gear ends up about 90-110 mph. He did mention gearing the absorber 2:1 to spin it faster. I will probably do that when I can. 

 
Posted : 06/09/2024 12:51 pm
(@philstubbs)
Posts: 16
Member
Topic starter
 

Here is a run with the new pump. The pump can flow 110 GPM and is the pump that came with the dyno. It is being fed from a 275 gallon tank that is mounted higher than the pump. All plumbing is 2 inches.

 
Posted : 07/09/2024 9:49 pm
(@philstubbs)
Posts: 16
Member
Topic starter
 

Ok, ignore that last post. After talking with Kevin Hamilton I realized my RPM1 sensor was incorrect. I have now changed that to the YourDyno wheel and sensor. It is definitely reading that correctly. This run is a Miata that should make basically 100 HP.

 
Posted : 08/09/2024 7:55 pm
(@philstubbs)
Posts: 16
Member
Topic starter
 

Forgot to add the file

 
Posted : 08/09/2024 10:10 pm
(@philstubbs)
Posts: 16
Member
Topic starter
 

 again

 
Posted : 08/09/2024 10:28 pm
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