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Originally posted by all_bark why did the sae corrected number RAISE the cat and LOWER the plenum but come out about the SAME?
Because it factors in environmental variables. Even dynos as close as 20 minutes can be skewed from the environment.
Unfortunately even SAE correction can be skewed, as some shops place the weather station in odd locations (but that is neither here nor there).
SAE corrected values should be used when comparing dyno runs from different groups, especially different days.
For example, on my base lines sae added power and on my plenum and header runs it took power away. Thus if I were to compare my baseline with my plenum runs as well as my header runs WITHOUT SAE correction I get much better numbers. I have always posted sae numbers, infact Doug and I are the only ones that I know for a fact used SAE on the top 10 N/A list. You should be up there now too. Now the question is which ones are you going to post? If you want to follow the crowd and post non corrected numbers then let me know cause I want to do the same. My 260 number jumps to 269 when I take SAE correction off.
Good numbers by the way!
__________________ 03 350Z Crawford 265 Cams, Plenum, Headers, Cats, Big Bore TB, Fujitsubo Ti Exhaust, TS ECU, JWT Intake, Clutch, Flywheel 05 G35 Sedan - 5AT
I know my Crawford charts didn't really change when I plotted them uncorrected. The baseline power went up and so did the Crawford power, but I didn't test two products, only one. And if I remember, it was about 32 degrees out with the same humidity and barometric pressure.
As Vandy mentioned, the SAE correction factor attemps to adjust the HP to what it would read if tested under standard temperature, pressure, and humidity (I don't know exactly what those standard values are, but they are probably online somewhere).
Because these variable will change throughout the day, you should ALWAYS use the SAE correction factor to compare results, otherwise it could simply be the change in weather that is changing the dyno numbers.
Since you were putting down more power "uncorrected", that means that you were getting more air than you would have received under "standard" conditions. Therefore, after applying the correction factor, some of the power was subtracted in an attempt to account for that.
If you had dyno'd on the top of a mountain in the middle of summer during a heat wave, the corrected number would probably be higher than the uncorrected number, but that would depend on what exactly the standard conditions are.
In any case, it is best to use the corrected numbers so that those variables are factored out as much as possible (of course, the correction is only as accurate as those variables, so if the temp sensor on the dyno is fubar'd, then your correction factor will be as well).
Originally posted by 350zdanny My tuner was telling me that depending on your location, some correction factors are better than others. I wonder if there is any truth to that. I'm sure there is or they wouldn't have them.
SAE is just the "standard" on the internet though. If you're posting, people want it in SAE.
I do not belive for one second "a smoothing constant of 3 is the best" like some have said here. I have taken about 4 statistics courses, and different methods of smoothing are appropriate for different conditions. So your tuner was correct. A smoothing constant of 3 may overcorrect the results. What if I'm at sea level, with standard temperature, pressure, and humidity? Assuming I am, why would I use a smoothing constant of 3? I would be very interested in knowing what statistical process is used to smooth these values. Having taken a time series class, possibly I could offer some input.
phile... The smoothing constant is something totally different than SAE correction. Smoothing constant means how much jitter do you remove from the dyno plot. A dyno measurement is not actually a contiguous line (as you well know due to your stats expertise) but rather a set of points. If smoothing is not done, those points look very jittery but smoothing can affect the HP number by a point or two.
SAE is a formulaic compensation for differences in altitude, humidity, temperature, etc (I don't pretend to know the exact formula). It tries to nullify the impact those factors have on the reported HP number. In a high heat, high humidity, high altitude situation your dyno would be artificially low because your car is competing with nature more than "normal" to push the car.
As a piece of anecdotal evidence, one of my most recent dyno runs was a whopping 15 HP higher uncorrected than the SAE number was!
SAE is normally recalculating your actual dyno results to sea level conditions for altitude (0), temperature to about 77 degrees, barometric pressure to 29.2 in/hg, and humidity to 0%. In the majority of cases, SAE correction will yeild higher numbers unless one of the adjusted variables creates a greater difference than the altitude at which the test is run. For instance, if you are at 800 ft but the humidity is 5% and temperature is 45 deg and barometric pressure is higher than 29, you will probably see a loss from correction even though you are at some altitude. Normally, the correction values will be more optimal for more power and will show higher numbers. What matters is that there is a standard that everyone uses for accurate comparisons.
GUYS, I think he is asking something TOTALLY different.
Notice, WHY is the increase in HP different in perportion (the 1st the cats HP is low/plenum high, while the next dyno shows a pretty even balance between the 2 mods) when comparing the SAE and non-corrected dynos, that is weird