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EFI Tuning Fundamentals: Standard Conditions

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Standard Conditions

02.35

00:00 - When we're testing engine performance, atmospheric conditions can have a significant effect on the result.
00:05 For example, let's say we dyno an engine in the middle of winter at sea level, and achieve 1,000 horsepower.
00:11 Now, we take that same engine, on a hot summer's day, and dyno it at high altitude, and now we may only see 900 horsepower.
00:18 The engine's identical, so why has the power changed? While the engine may be consuming a certain volume of air, measured in cubic feet per minute, what we're really interested in, is the amount of oxygen present in that air.
00:31 This is because it's the oxygen molecules that we need to mix with the fuel.
00:36 Atmospheric temperature and pressure, both have an effect on air density, and this in turn affects the number of oxygen molecules that are present.
00:45 As altitude increases, air density, and hence oxygen content, decreases.
00:50 What this means is that if we take an engine and measure the power it produces at the top of a mountain, the result would be lower than if we did the same test at sea level, because there are less oxygen molecules present in the same volume of air.
01:04 Likewise, as we raise the temperature of the air, its density drops, and hence, hot air contains less oxygen molecules.
01:11 This means that if we test our engine in the middle of summer with a high air temperature, the result will be lower than if we tested in the middle of winter with a low air temperature.
01:21 So that we can provide some consistency in our testing, the scientific community has come up with a set of operating parameters, referred to as standard conditions.
01:31 These standard conditions offer a benchmark for air temperature and pressure, so we have a baseline to compare against.
01:38 The standard air pressure at sea level is defined as 101.3 kPa, or 14.7 PSI, while standard air temperature at sea level is defined as 15 degrees centigrade, or 59 degrees Fahrenheit.
01:54 As long as we know the air pressure and the air temperature that an engine's operating at, then we can correct the power output back to what the engine would produce under standard conditions.
02:05 This is the basis of the power correction methods employed by dyno manufacturers.
02:10 This theory also means that we can directly compare power figures from engines tested under vastly different atmospheric conditions.