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Actually, SAE uses a correction factor so all numbers off the same dyno, but under varying atmospheric conditions are comparable. SAE takes into consideration ambient air temp, humidity, elevation, etc. so to say there is a certain change in the numbers universally is not correct. If you would tune at exactly the conditions that the SAE baseline is set, the correction factor could theoritically could be zero.
More to Dalton's point. Ideally, every dyno pull would be done under identical atmospheric conditions. This is seldom the case, so a power correction factor (CF) is applied to a measured power reading to compensate for changes in barometric pressure, temperature, and humidity. Theoretically, the power CF helps make it possible to compare dyno runs performed at different locations and under different atmospheric conditions, but it is not 100% accurate. The most common correction factors used are STD (Standard), SAE (Society of Automotive Engineers), and DIN (Deutsche Industrie Norm). SAE uses less favorable atmospheric conditions than STD or DIN, and it is the most frequently used for rear wheel testing, however STD is becoming more the standard. Lower correction factors also tend to be more accurate. It is important to remember however that a CF is only intended to compensate for small atmospheric differences and doesnt correct for other factors, such as engine and oil temperatures.
I woud agree with Phoenix that 2.6%-2.7% is a reasonable factor for you to use to convery your data from STD to SAE.
at any given day depends on air conditions humidity and hot or cold the sae numbers can be the same as std or uncorrected. look at my signature uncorrected and sae numbers.
also the correction factor should be as close to 1.0 as possible depending on conditions and altitude the higher you go the more of a cf will show but you are actually making less power but sae will compensate as if it was at sea level but the bike is making less power.
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