STP Corrected Dyno Results
- Thread starter stang99
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What did they do to "solve" the high readings? Did you get abnormally high numbers too and then they corrected something?
I found this about STP, but they were also talking about BHP. I don't know how that works out at the back tire.
"The STP standard is another power correction standard determined by SAE. This standard has been widely used in the performance industry. Power is corrected to reference conditions of 29.92 In Hg, 60º F, with dry air. Because the reference conditions include higher pressure and cooler air than the SAE standard, these corrected numbers will always be about 4% higher than SAE power numbers."
Those look like sea level conditions. Isn't sea level something like 29.92 InHg, 59º F, 0% humidity?
"The STP standard is another power correction standard determined by SAE. This standard has been widely used in the performance industry. Power is corrected to reference conditions of 29.92 In Hg, 60º F, with dry air. Because the reference conditions include higher pressure and cooler air than the SAE standard, these corrected numbers will always be about 4% higher than SAE power numbers."
Those look like sea level conditions. Isn't sea level something like 29.92 InHg, 59º F, 0% humidity?
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Tetge,
There were a whole bunce of 03's at Fontana today. Mysteriously,
there wasn't a 382.7 RWHP white one. I wonder who it was that started the lets go to Fontana Saturday tread?
There were a whole bunce of 03's at Fontana today. Mysteriously,
there wasn't a 382.7 RWHP white one. I wonder who it was that started the lets go to Fontana Saturday tread?
The conditions given above for "STP" are essentially the same as what we know as "STD" - sea level. By the book, it should be 59F vice 60, but that's close enough, and all the other numbers are right.
To convert to SAE, simply subtract 2.5% - that will get you real close (about 373 RWHP).
BHP is measured at the flywheel, and cannot be accurately measured with a chassis dyno (though it can be guestimated by taking ~45 HP off the RWHP number).
To convert to SAE, simply subtract 2.5% - that will get you real close (about 373 RWHP).
BHP is measured at the flywheel, and cannot be accurately measured with a chassis dyno (though it can be guestimated by taking ~45 HP off the RWHP number).
STP = Standard Temperature and Pressure. Standard Temperature is the freezing point of water (273K-->0-degC-->32-degF) and Standard Pressure is the pressure of atmosphere at sea level (101.3kPa-->1atm). Standard Pressure is more important for corrections than standard temperature
STP does not equal Standard Temp and Pressure on the Superflow Dyno.
The SuperFlow WinDyn software will automatically convert the dyno results to SAE and report them as CWhlTq and CWhlPw (Channel Wheel Torque / Power).
Two additional inputs into the system adjust for tire friction power loss and drivetrain efficiency (manually input). The software adjusts for these to report flywheel torque and horsepower as STPTrq and STPPwr.
The correction factors on my dyno runs were 0.02 for tire loss and 0.90 for drive train efficiency. Resulting in an assumed 0.90 * 0.98 = 0.882, the correction factor to compute flywheel numbers from the RWHP and RWTQ was 1 / 0.882 = 1.134.
The SuperFlow WinDyn software will automatically convert the dyno results to SAE and report them as CWhlTq and CWhlPw (Channel Wheel Torque / Power).
Two additional inputs into the system adjust for tire friction power loss and drivetrain efficiency (manually input). The software adjusts for these to report flywheel torque and horsepower as STPTrq and STPPwr.
The correction factors on my dyno runs were 0.02 for tire loss and 0.90 for drive train efficiency. Resulting in an assumed 0.90 * 0.98 = 0.882, the correction factor to compute flywheel numbers from the RWHP and RWTQ was 1 / 0.882 = 1.134.
Well then on the dyno STP is a misnomer, because in chem. STP equals to standard temperature and pressure. I figured it was strange as STP is used to calculate volumes of gases and such
A Standard Atmosphere is 59F (15C), 29.92 in/hg (1013.2 mb), and 0 % humidity. That is what a dyno operator should be correcting to if he/she is not using SAE. As it pertains to this discussion, STP is just another term for STD - both are a "Standard Atmosphere".
SAE is 77F, 29.23 in/hg, and 0% humidity.
The difference in power correction is about 2.5%, with STD always being the higher one. For examples, see the links below. Same dyno, same day, same car, no changes except the correction factor:
STD Dyno Graph
SAE Dyno Graph
SAE is 77F, 29.23 in/hg, and 0% humidity.
The difference in power correction is about 2.5%, with STD always being the higher one. For examples, see the links below. Same dyno, same day, same car, no changes except the correction factor:
STD Dyno Graph
SAE Dyno Graph
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Here's some info on correction factors.
http://www.superflow.com/support/cycledyn-theory.html#SAE
http://www.superflow.com/support/cycledyn-theory.html#SAE
Tetge--The only numbers which make sense to use are SAE or STD numbers, and it is precisely because weather conditions change and people dyno their cars at various elevations. Corrected the raw measured torque and horsepower numbers to a set of standard conditions makes it possible for you to compare the numbers you just got to numbers taken next summer on a different dyno with different humidity and elevations.
A couple of years ago, no one ever used anything but the SAE conditions stated above. As far as I am concerned, those are the conditions you should get your results in.
The correction is strictly an air density correction taking into account the humidity, air pressure (due to elevation and small changes in barometric pressure), and temperature. The correction applies to gas turbines exactly as it does to internal combustion engines.
You can't apply the full correction to a nitrous engine because the power derived from the oxygen in the nitrous is not affected by the dyno atmospheric conditions.
Joe Lynch
A couple of years ago, no one ever used anything but the SAE conditions stated above. As far as I am concerned, those are the conditions you should get your results in.
The correction is strictly an air density correction taking into account the humidity, air pressure (due to elevation and small changes in barometric pressure), and temperature. The correction applies to gas turbines exactly as it does to internal combustion engines.
You can't apply the full correction to a nitrous engine because the power derived from the oxygen in the nitrous is not affected by the dyno atmospheric conditions.
Joe Lynch
Superflow after analyising my run saw the incorrect parameters that were used. He didn't say which ones were wrong but the new numbers I got are much more consistant. And comparing them with Tetges' run makes it more believable.
Mine:
WHlpr obs hp: 386.1 (uncorrected actual high altitude hp)
CWhlPw STP hp: 430.1 @ 6369 rpm
STPPwr CHp: 547.6 @ 6369 rpm (Flywheel Hp)
DWhTq Clb-ft: 401.1 @ 4055 rpm
STPTrq Clb-ft: 504.9 @ 4055 rpm (flywheel Tq)
STPCor Factor: 1.114
Baro P InHga: 27.57
AirInT DegF: 79.4
Drivetrain loss used was 15%
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Exactly! Although the printout says STP, for all intensive purposes it's SAE. WinDyn breaks it down as follows:
WhlPwr obs: actual uncorrected rear wheel numbers
CWhlPw: STP altitude corrected RWhp
DWhlTq: STP altitude corrected RWtq
STPPwr: STP altitude corrected FWhp
STPTrq: STP altitude corrected FWtq
Why the heck would they call it STD if it is actually calculated to the SAE conditions? It IS significant.
Joe Lynch
Joe Lynch
So if I'm reading this correctly, you're supposedly losing 117 HP through your transmission and differential? No way in hell...unless you had the emergency brake on.
Are these your new numbers? That seems to be much more in line. Still good numbers BTW.:beer:
That's with a 15% drivetrain loss calculated. Superflow actually wanted him to use 16-17% loss but that seemed too excessive. If you want to add Hp back into my numbers, by all means go ahead I won't complain.
03DOHC,
Yes these are the new numbers, I redyno'd on Friday. I got a little busyand hadn't got around to posting them until now.
That 15% number that everybody passes around is bogus. In fact, any set percentage is bogus.
That said, even if you used 15%, it would still only be 81 HP - not 117.
That said, even if you used 15%, it would still only be 81 HP - not 117.
:shrug: I am doing the best I can with the information available. I must assume the dyno operater and manufacturer are professionals to be trusted. I am merely passing on the translation of the data as explained to me. I can take a guess and say that it's just the way Superflows software labels the data. Maybe someone else owns the "SAE" or "STD" labels and they can't use it. I'm just taking a guess here so don't torch me for it. And since some of can't just pop into any dyno facility any time we feel like it we accept what we're given. SAE, STP and STD shouldn't cause such a debate when the Board estimated differences are miniscule IMO. And if people are that worried about the differences then I propose THEY do a comparison run. I don't have the time or money to do it nor will I have my car labeled a Dyno queen. IMO It's all about having pride in your car and the work you do or have done. Unless it's a gross error, like my first run, then why can't we stop ripping on peoples dyno or track runs?????
FWIW, I am not intentionally "ripping" on anybody or their ride. I am merely trying to clear up a few things.
My personal opinion on dyno's is that they are excellent tuning tools - little else. They are great for seeing what mods work, what tuning works, etc. I don't put much stock in the absolute numbers.
My personal opinion on dyno's is that they are excellent tuning tools - little else. They are great for seeing what mods work, what tuning works, etc. I don't put much stock in the absolute numbers.
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