Coles Notes
In short, STD, is the oldest scale. Has been around forever, corrects to 60F yields roughly 4% higher numbers on the Dyno.
In short, SAE, is the Newest scale(1990), Claimed as the "Honest man's Scale" correct to a more realistic 77F. Not the best scale for Arm Chair Bragging Rights but gives the best real world results.
The smoothing is just that, gets rid of the peaks and valleys (up to a point) to give you a more accurate (average) reading. I like seeing smoothing 5, some people like 1 as it usually gives an inflated peak number that the power band can't substain.
In most cases, to many look for just the Big Dyno numbers. Important to note, Without seeing Your before Mod hp #'s and then the After Mod hp #'s it's very hard to judge the Mod value of your gains. Always ask for the before and after sheets if your paying, look for same scale.
Hundreds of articles out there on this. Hoped this save you some time. Cheers see quick read below.
STD Correction
STD, or standard correction, represents one of the oldest correction factors used by the Society of Automotive Engineers (SAE). STD is also known as J607 and it uses standard conditions of 60-degrees F, 29.92inHg and 0-percent humidity. For you engine dyno enthusiasts, these factors should look familiar, as STD (J607) is one of the most popular correction factors available and used almost exclusively by NASCAR teams to compare results from chassis dyno testing to results from the engine dyno. STD is also one of the most stable correction factors, in that it has not been changed for many years and the ideal factors remain consistent.
SAE Correction
SAE J1349 is the current gold standard of dyno testing and represents the newest widely accepted industry standard correction factor. Reengineered in 1990 (yeah, a long time ago), the SAE correction factor standardizes temperature to 77-degrees F, 29.23inHg and dry, 0-percent humid air. We exclusively use SAE correction when testing parts and cars here at GMHTP and your dyno operator probably does too. SAE, unlike uncorrected or STD, also uses a mechanical efficiency (friction) modifier in the correction factor, which assumes an 85-percent mechanical efficiency or a 15-percent differential in engine power due to frictional loss, which is fairly accurate in a standard all-motor application. Now, if you're thinking this means it reads 15-percent higher, that is not the case at all. In fact, SAE, due to the higher and more realistic standard temperature and absolute pressure factors will normally read 4-percent lower than a dyno graph printed in STD. It is important to note that there are other correction factors, but STD and SAE are the two most popular and commonly used (especially in the States).
Real Wheel Horsepower
Understanding correction factors and the math involved can be a fun mental exercise, but the real point here is to understand how dyno graphs can be compared and what to do if you're comparing two graphs from similar cars tested in different environments. First and foremost, you need access to the original weather station data (Temp, Atmospheric Pressure, Humidity). Without this basic info, comparisons are impossible, so make sure you have it. Luckily, on any Dynojet, these numbers are sampled and recorded for every run and are always saved with each runfile, so if you don't have them handy, a quick call to your local dyno shop is all you need to get the weather station data. Secondly, you need to be able to see what correction factor was applied to your graph at the time it was printed. On any Dynojet graph, for example, you should see this information printed on the top right hand corner, where it will say something like "SAE, Smoothing 2." If you don't see these numbers on a graph you find on the Internet, start getting suspicious, you may be looking at an altered graph or, at the very least, something run with a strange correction factor to make the numbers look higher than they really are.
