Q&A Forum
I recently acquired the shop and dyno that I originally set up for the previous owner. I opted to configure a brand-new PC and install the latest YourDyno Una Vision software. The dyno's inertia parameters are dialed in correctly; I get very clean, repeatable data in inertia-only mode. On the test truck I’m using right now, inertia pulls consistently show about 270 wheel torque.
The issue is that when I switch to a brake-controlled power sweep, reported torque drops to roughly 140 wheel torque, less than half of the inertia value. Everything else appears to be functioning normally: the brake responds to commands, RPM pickup is clean, and the load cell zeroes properly.
I have attached screenshots of the power sweep configuration and load cell setup screens.
Any ideas of what I'm doing wrong?
Here is the sequence of calibrating a new setup:
- Ensure the number of pulses per revolution is correct in the RPM setup
- Calibrate the load cell(s). The procedure is described in the UnaVision manual
- Dial in the brake settings so a Power sweep or Load control run is smooth
- Measure the Moment of Inertia. There are several ways to do it. I like to do one inertia only run and one slow brake controlled run. It is essential here that the braked run is much slower than the inertia run. Adjust the MOI such that the inertia run and the braked run overlap as much as possible. For the inertia measurement, choose a car that
- Does not change gear during the run
- Has a very tight torque converter (best with a manual or double clutch car)
- Does not heat soak or adjusts the turbo pressure or similar based on the load or anything else that would make the engine perform differently in the two runs. Also make sure the air in the shop is clean for both runs
- Select Power correction % and or Retardation measurement as you want
- I always recommend doing the retardation measurement, as it will include the unmeasured losses in the dyno, as well as the unloaded losses in the tires and drive train
- In addition to the retardation measurement, you need to add some Power correction if you want engine power. For an efficient drive train, 5% is typical
Note that when you search for the right MOI, you can change the MOI and click the re-run button on the two runs you are comparing. No need to do the physical runs again