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Dyno Corrections: What are they and when do we want to use them?

The question often arises when someone quotes power: were those numbers corrected? It is a valid question, and depending on what you are trying to do or investigate may or may not be important. There are a couple of things to discuss. The first is the different types of corrections out there. The second, when do you want to correct?

This discussion is meant to give you an idea of why we do corrections and when we apply them, not to actually discuss the specifics of the different standards. A lot of this comes down to definitions and terminology. For example, most of the standards that are presently used are defined by the Society of Automotive Engineers (SAE). When something is corrected to those standards it is often said that this run was “SAE Corrected.” Now, one of the problems with this is that SAE has a few different standards which are frequently used in the industry. So, if I say that this is SAE corrected how do you know which one? One of the main differences between the various specs is what they consider to be a “normal environment.” After all, that is all that these formulae do. They correct the numbers coming out of the dyno for the environment. There are many factors that go into these calculations. Among them are temperature, humidity, pressure, and altitude. The J607 specification uses a temperature of 60 F as “normal” compared to J1349 (or J1985) which used 77 F. This means that if you use both systems with the same set of data you will get higher results for HP/TRQ with the J607. That means you cannot compare corrected data from the two different systems.

This leads to the next point. Many of you have noticed that on cool days it seems like your car runs faster than on hot days. That is because it does. If you had a perfect driver on a perfect course and the only difference in the world was the temperature you would run faster times on the cold day. That is because you are making more power on the cold day. This is why I asked when do you want to correct. You want to correct when you are doing before and after comparisons or when you are comparing different cars. This is because you need an equalized way of telling if there is a difference. If I ran my car at 50 F and you ran yours at 90 F, I will physically be making more power than you. That does not tell me however if we had both of our cars side by side in the same environment who would have better results. Now, if you wanted to know how fast your car was running on a particular day, you would not want to correct. For example, if I were going to race today I might want to know what my “real” output is so that I can be prepared for how the car will perform.

The thing to remember is your “real” results are the uncorrected numbers. That is what your car was actually doing during the dyno run. But, for the purposes of the Dynoperformance d-base for example, we only want corrected numbers because we are looking at before and after situations and trying to compare different cars and we need a way of taking out the environmental variations. If we couldn’t equalize the test environment, then we would never be able to tell if something made a difference.

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