Author Topic: So what does SAE mean on a dyno sheet?  (Read 6933 times)

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Offline brutus1

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Re: So what does SAE mean on a dyno sheet?
« Reply #25 on: August 31, 2012, 06:57:54 AM »
Is it true that dynojet has their own correction factor? Or in other words a fudged SAE? SUPERFLOW has a dynojet comparison and IMO a true SAE factor. Everyone likes the dynojet numbers because
 they are always higher than true SAE. Should we adopt dynojet numbers as the new SAE?
 

Offline Rider57

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Re: So what does SAE mean on a dyno sheet?
« Reply #26 on: August 31, 2012, 10:27:57 AM »
Adopt what suits you. Facts are facts, and that will never change.
107ci, 408b, 10:5:1, Heads by Wes Brown, Thunders.

Offline Mirrmu

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Re: So what does SAE mean on a dyno sheet?
« Reply #27 on: May 08, 2015, 04:00:39 PM »
quite often you will see a baseline run with conditions very different from final build run, humidity maybe 35% then would be 9% for example, with the correction factor still 1.01 or 1.02 or 1

what does that all mean? and do you get such wide variances when quite often these are controlled, well insulated specific built rooms?

Offline FLTRI

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Re: So what does SAE mean on a dyno sheet?
« Reply #28 on: May 09, 2015, 09:41:36 AM »
quite often you will see a baseline run with conditions very different from final build run, humidity maybe 35% then would be 9% for example, with the correction factor still 1.01 or 1.02 or 1

what does that all mean? and do you get such wide variances when quite often these are controlled, well insulated specific built rooms?
This may help:
The Society of Automotive Engineers (SAE) created the SAE J1349 JUN90 standard method for correcting horsepower and torque readings so that they will seem as if the readings had all been taken at the same "standard" test cell where the air pressure, humidity and air temperature are held constant. Furthermore, the SAE J1349 JUN90 standard includes an assumed mechanical efficiency of 85% in order to provide an estimate of the true engine horsepower (without accessories).

The equation for the dyno correction factor given in SAE J1349 JUN90 (for normally aspirated gasoline engines), converted to use pressure in mb, is:

                sae equation jun90

                        where:   cf = the dyno correction factor
                                     Pd = the pressure of the dry air, mb
                                     Tc = ambient temperature, deg C

The pressure of the dry air Pd, is found by subtracting the vapor pressure Pv from the actual air pressure. For more information about pressures and calculation of the vapor pressure, see Air Density and Density Altitude.

The relative horsepower is simply the mathematical reciprocal of the correction factor.
SAE J1349 Update:

In August 2004 the SAE released  J1349 Revised AUG2004 which specifies that the preferred method of determining the friction power used by the motor accessories is actual measurement, and that the assumption of 85% mechanical efficiency (as formerly used in SAE J1349 Revision JUN90) should only be used when actual friction data are not available.

The equation for computing brake horsepower (for normally aspirated gasoline engines), assuming 85% mechanical efficiency, was very slightly revised (and is presented here converted to use pressure in mb) as:

                 sae equation aug04
 

Section 5.1 of the SAE J1349 AUG2004 revision also makes it clear that this correction factor is note 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, and the intended range of dry air pressures is 900 to 1050 mb.


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Offline HD Street Performance

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Re: So what does SAE mean on a dyno sheet?
« Reply #29 on: May 09, 2015, 09:14:51 PM »
The formula:
https://app.box.com/s/wnqspu2395hzxrptjx4r65rlvkfu1ipr

For reference

Temperature range  corrected to F:
+59F to +95F

Barometric Pressure range converted to inches of Hg
26.58" to 31.00"
FYI and FWIW average air pressure, barometric at 4,000ft altitude is 25.8" and out of this correctable range during average weather conditions

Online 1FSTRK

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Re: So what does SAE mean on a dyno sheet?
« Reply #30 on: May 13, 2015, 05:11:27 AM »
quite often you will see a baseline run with conditions very different from final build run, humidity maybe 35% then would be 9% for example, with the correction factor still 1.01 or 1.02 or 1

what does that all mean? and do you get such wide variances when quite often these are controlled, well insulated specific built rooms?

The dyno jet booth is not a climate control booth like you would find at a auto manufacturer or F-1 team. They are mostly for noise dampening and exhaust evacuation so the weather conditions are monitored rather than controlled. If not purposely manipulated, or skewed by incompetence, the dyno actually does a good job of correcting for the environmental changes that take place in the booth during testing.
If you run the formulas there are many different combinations of conditions that yield the same correction factor.       
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