Dyno Correction Factor Calculator (DIN 70020 and SAE J1349)
The factor that converts power measured on a dyno on the day to standard atmospheric conditions, by DIN 70020 or SAE J1349, and the corrected power.
Results
The dashed line marks the value you entered.
What this tool does
Engines make less power in thin, hot, humid air, so dyno results are scaled to a reference atmosphere to make them comparable. DIN 70020 corrects to 1013 mbar and 20 °C using the absolute pressure; SAE J1349 corrects to 990 mbar of dry air and 25 °C, which is why it needs the humidity, and its 1990 form also folds in an assumed 85 % mechanical efficiency so that it reads somewhat lower. The same engine therefore reads differently under each standard. Always quote which one was used, and do not mix results.
Formula
DIN 70020: CF = (1013 ÷ p) × √((273 + T) ÷ 293) · SAE J1349 (1990): CF = 1.18 × (990 ÷ p_dry) × √((273 + T) ÷ 298) − 0.18 · p in mbar, T in °C
Variables
| Symbol | Meaning | Unit |
|---|---|---|
st | Correction standard | — |
pb | Air pressure on the day | hPa |
ta | Intake air temperature | °C |
rh | Relative humidity (used by SAE only) | % |
pw | Power measured on the dyno | — |
CF | Correction factor | — |
PC | Corrected power | — |
PV | Water vapour pressure | hPa |
Worked example
- Correction standard1
- Air pressure on the day1000 hPa
- Intake air temperature25 °C
- Relative humidity (used by SAE only)40 %
- Power measured on the dyno200
- Correction factor1.022
- Corrected power204.3
- Water vapour pressure12.7 hPa
Limitations
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.