The best way to determine the right amount of extra timing is to test. As we explained above, relative humidity percentages are not an accurate measurement of the amount of water vapor in the air. It’s kind of like nature’s water injection since there is more water vapor in the air ingested by the engine, the chance of detonation decreases.Īn old racing rule of thumb states you can add one degree of timing for every 10 percent increase in humidity, with a maximum of four degrees of extra timing. There are three inexpensive tuning tools and one driving tool you can use to compensate for changes in weather conditions:Īs dew point and air temperature get closer together (there is more moisture in the air), you can increase ignition timing. You can find a detailed explanation on the relationship between dew point and humidity at. Good sources for local dew point information are airports close to the track or National Weather Service radio and online reports.ĭew point provides a much better gauge of moisture content in the air than the relative humidity percentage in your local weather report. If air temperature and dew point match, you will see liquid water in the form of dew, fog, or rain. The difference between air temperature and dew point indicates how close the air is to saturation.
The dewpoint is always lower than or equal to the air temperature. It is the temperature at which air can no longer hold all of the water vapor, forcing some of it to condense into liquid water. The true amount of water vapor in the air varies with temperature, even if the relative humidity percentages stay constant.ĭew point is a better way to accurately measure water vapor in the air. Water vapor in the air is better known as humidity. While useful for tuning, dyno results don’t reflect real-world conditions where temperature and humidity are always changing. When an engine is tested on a dyno, the results are corrected to “dry” air, which means air with no water vapor. But first, some schooling on what weather does to your engine. We’ll show you four tricks of the trade to compensate for weather conditions. Now that stout motor feels like it lost 90 horsepower.Ĭan you recover some of that lost power? Yes you can, and without having to spend a lot of time and money. The barometer reads 29.20 inches of mercury and the relative humidity is a mere 74 percent. The thermometer now reads 96 degrees and track surface temperatures are well into the triple digits. The engine runs perfectly on a cool spring day when temperatures and humidity are close to the ideal dyno corrected figures (60 degrees F, 29.92 inches of barometric pressure, zero-percent humidity).
Here’s a scenario to ponder: You hand picked the best components for an engine build, had those bits meticulously machined and assembled, and ended up with a stout engine that made 850 horsepower on the dyno.
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