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Originally Posted by SYZ
see highlighted portion of where I got the number. I didn't realize altitude is not in the equation. Seem like it should be however, since SAE is supposed to be at sea level. Why have that as a standard if you don't compensate for it?
Edit: did a little research, amazing
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Yes, that is a great web site and the one I reference most often. If you want even more information, you can purchase and download SAE-J1349 horsepower and correction specification, although that's probably unecessary because that web site shows the actual formula (see link below).
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Originally Posted by Skooterbrah
Altitude isn't considered for SAE corrections???
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Not directly, no. Air pressure is affected by altitude. So altitude is compensated, but only by virtue of it's effects on absolute air pressure. I hope that makes sense.
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Has it always been this way?
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Yes.
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I was under the impression that altitude was definitely part of the correction factor....
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Not directly, no. Altitude is compensated indirectly through it's effects on absolute air pressure. This page shows the actual SAE formula:
http://wahiduddin.net/calc/cf.htm
You can see that Altitude is not in that equation. The equation shows the use of absolute air pressure "Pd" and does not include altitude. If you don't have Pd measurements, then there's ways to calculate it. One way of calculating Pd is with dew point and altitude. So altitude is in there...but only as a means to calculate absolute air pressure.
Other ways to calculate Pd are with humidity and barometer -- just like the dyno. If you want to use the same formula the dyno uses, then use this page and type in your numbers.
http://wahiduddin.net/calc/calc_hp_abs.htm
If you type in your numbers of 90.62F, 1008hPa, and 36% humidity, then you get a correction factor of 1.5% -- which is far different than what I said yesterday. Yesterday I made a mistake and calculated "STD" correction, not SAE correction. The SAE correction for those settings would be about 1.5%.
You might want to compare the barometer on the dyno with a valid weather station in the area. I'm sure you will find the dyno barometer is not close to accurate.
Anyways, I hope this helps.