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Mark@GTPumps

Dyno correction factors

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Dyno Correction Factors Explained.

Mark Boxsell. M SAE

The whole point of a dyno correction factor is to be able to test in different atmospheric conditions (eg. summer, winter, different locations) and to still be able to compare the results from any given test.

As the engine relies on mass air flow to make power any change in air density can have a large effect on the output of the engine. If the air is more dense (lower temperature, lower atmospheric pressure) you will make more power, if the air is less dense (higher temperature, higher atmospheric pressure) you will make less power.

So what happens is a "standard air condition" was created. A formula was then derived taking into account the air density components (temperature, pressure and humidity) that allows a correction factor to be calculated.

This correction factor is applied to the measured power to give a result AS IF THE ENGINE WAS ACTUALLY OPERATING on a day with " standard air conditions".

As it happens there are a few different correction standards!

The Dyno Dynamics dyno uses SAE J1349 however with the Mainline dyno you can select from a number of corrections including SAE J1349 however most people use J607.

The main difference between J1349 and J607 is the "standard" operating conditions chosen.

SAE J1349 "standard conditions"

Barometric pressure = 990 mb

Humidity = 0%

Temperature = 25 degrees C

SAE J607 "standard conditions"

Barometric pressure = 1015 mb

Humidity = 0%

Temperature = 15 degrees C

For example another non automotive standard

International Civil Aviation Organization (ICAO) "standard conditions"

Barometric pressure = 1013.5 mb

Humidity = 0%

Temperature = 15 degrees C

To highlight the difference at 20C the J1349 correction would subtract power and the J607 correction would adding power!

The difference in the "standard day" conditions chosen means for any given conditions J607 will always read higher than J1349.

So some points.

1) To compare dyno data both dynos have to be using the same correction factor!

2) To compare Dyno Dynamics data with Mainline data the Mainline dyno needs to select J1349 for the print out. This can be done with the Mainline dyno as the raw data is saved so you can select either correction standards when printing out results, or even print out both.

3) The position of the intake air temperature (IT) sensor on the Dyno Dynamics is very important as it can dramatically effect the correction factor.

4) With the Dyno Dynamics dyno the barometer pressure must be entered by the operator as read from the dyno shops own barometer, this also can dramatically effect the correction factor

5) The local barometer pressure typically published for weather purposes is a altitude corrected pressure (corrected-to-sea-level atmospheric pressure ) not the actual atmospheric pressure.

Example correction.

Dyno test conditions

Barometric pressure = 932 mb

Humidity = 68%

Temperature = 19 degrees C

J607 correction = 1.114

J1349 correction = 1.081

Base "uncorrected measured power" 236kW

J607 corrected power = 262.9 kW (Mainline J607 selected)

J1349 corrected power = 255.1 kW (Dyno Dynamics)

Note: Section 5.1 of SAE J1349 AUG2004 standard makes it clear that the equations are not intended to provide accurate corrections over an extremely wide range, but rather that the intended range of air temperatures is 15 to 35 deg C (59 to 95 deg F), and the intended range of dry air pressures is 900 to 1050 mb (26.58 to 31.01 inches-Hg). Values outside of this range may produce inaccurate results for SAE Relative Horsepower and Dyno Correction Factor, but all other calculator results (such as Density Altitude, Air Density, etc) will still be correct.

SAE is short for Society of Automotive Engineers http://www.sae.org

Happy dyno testing from www.gtpumps.com.au

Edited by Mark@GTPumps

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Guest Sidney

There is a number on the field labeled Correction in the mainline dyno print out, in front of SAE J607 and I've noticed it changes from print out to print out 

 

What does this number mean?

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