Question about SAE factor on a DynoJet run...

[ScortLX]

Ok everyone, I just had a question. I've been looking at DerekStangGT's dyno thread here on the board and I'm confused. Here is the link: http://forums.stangnet.com/showthread.php?t=699532. Looking at the graph, they were using a SAE correction of 1.05 on the dyno run. I have a dyno run I had done on a DynoJet recently and it has a SAE correction of 1.24. What would the difference be? I don't know what that factor number actually does to the results. My numbers were 246hp and 284 tq with the 1.24 correction. How would that compare to his numbers (for example) with the correction of 1.05? I'm just not sure how the factor is used in the calculation of the numbers If anyone could help that would be great!

 

[WillDuhhBeast]

I always get confused when people start talking about corrected numbers and stuff. I have never even recieved "corrected" numbers for my car. I know that uncorrected I put down 373 to the wheels. Does that mean corrected would be more?

And do the numbers you describe vary depending on location? Blah.. technicalities.

 

[hotmustang331]

From my understanding there are 3 modes that a dyno can do.

Uncorrected (ACTUAL RWHP made on the dyno...doesnt factor in weather or altitude)

STD (RWHP that would be made if the car was at a DA of 0...IE sea lv)

SAE (RWHP that would be made on a standard day...not sure what altitude it is)

Most people use SAE...its #s always seem lower than STD, so apparently its more realistic. Uncorrected varries. If you dyno @ sea lv and its 50*s out with a 30 baro and 0% humidity, your uncorrected #s will be higher than SAE or STD as you would be in - DA. (density altitude)
Basically SAE just levels the playing field to a generic weather so no matter where you are or what the weathers like, you can compare dyno #s with anyone else in the world with noone having an advantage.

1.0 on the SAE correction factor means that SAE did nothing to correct the #s. So in otherwords I believe its like having uncorrected #s....means your day was close enough to "standard" that it didnt have to alter anything.
1.24 means that it multiplied your ACTUAL uncorrected #s by 1.24 to arrive at your current dyno #s.
And a .98 correction factor means that it DROPPED your uncorrected #s in the same manner because you were running on a better than standard day.

Its pretty accurate, but the outside temp can vary a few *s and it will stall say 1.0 correction...so it doesnt instantly respond if the temp outside rises a bit. So your #s can very a little bit due to the weather and it will still read the same correction factor.

Thats the way I understand it. Others here know more.

 

[WillDuhhBeast]

That explains a lot. Very good.

I've had my car dyno'd from two different places, and both gave me uncorrected numbers. I wonder why that is. I mean, I know I'm at sea level.. but 95* weather and 90% humidity can't be a great dyno day =(

 

[Stan Weiss]

The correction factor is calculated using Barometric pressure, temperature, and humidity. A correction factor of 1.24 is pretty high. along with your 95 degrees and 90% humidity your would need a barometric pressure of about 27.3. A standard day is 29.92 BP 60 degrees and zero humidity for SAE J816 and J607. Ford uses SAE J1349 to rate our engines which is 29.31 BP 77 degrees.

 

[ScortLX]

On the run in which the 1.24 SAE was being used here is the other data: 68.62 degrees F, 24.20 in-Hg. Keep in mind this is also at an altitude of about 5000ft. Does that seem right?

 

[hotmustang331]

Yep, VERY VERY low pressure. In aviation a standard day is 29.92 pressure...looks like SAE usues the same according to stan. So your pressure is MUCH lower than ours...obviously lol.

 

[ScortLX]

Great..thanks for the help. I'm using the same dyno that I went to on that run to do my before/after numbers for the TrickFlow Intake for everyone to see. Seems as though the correction was within a normal range because of the pressure. Thanks again!

 

[hotmustang331]

I just plugged some #s in, and with the info you gave along with a guess of 30% humidity....its showing up at like a 13,000 ' DA! SO yea thats why your correction factor was SOOO high....you had a super low pressure over your area.

I just looked up your current weather in your town and it reads.

6100 ft / 1859 m

38.3 °F / 3.5 °C
Light Rain
Humidity: 85%
Dew Point: 34 °F / 1 °C
Wind: 17.3 mph / 27 km/h from the North
Wind Gust: 17.3 mph / 27 km/h
Pressure: 30.03 in

That works out to a 6138' DA.

Im just not used to seeing pressure vary that much...so I looked around and a few places in new mexico are in the 24-25 Hg range, and most are in the 29-30 range. I have personally never seen it go that low where im at, so I decided to check it out and make sure I wasnt giving you false info. But you just happened to dyno on a HORRABLE day lol. I didnt realize it was actually that bad haha....but none the less, SAE correction took over and corrected everything. So it SHOULD still be accurate.

Looking forward to your #s!

 

[ScortLX]

I'm looking forward to the numbers too! I will let everyone know when I get the intake and give a time frame of the dyno run results. I'm guessing it should all be done by the second week of June. Thanks again for the help!