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Discussion Starter · #1 · (Edited)
http://www.csgnetwork.com/relhumhpcalc.html


This Relative Horsepower Calculator determines the relative torque and horsepower available at any temperature, barometric pressure, humidity, and altitude. The calculations are derived from public domain information, SAE J1349 Revision, June of 1990. The calculator shows you how much the air conditions on any given day will alter the horsepower of a normally aspirated internal combustion engine. This calculator uses relative humidity which requires some caution because the relative humidity changes radically during the day as the air temperature changes. To use this calculator, just enter the temperature, barometric pressure, humidity and altitude and click on the calculate button. Air density is affected by the temperature and humidity of the air. On a hot day, or at high altitude, or on a moist day, the air is less dense. A reduction in air density reduces the amount of oxygen available for combustion and therefore reduces the engine horsepower and torque. This calculator shows you how much the air conditions on any given day will alter the horsepower of a normally aspirated internal combustion engine. For example, at 85 degrees F, 30.14 Inches Hg (mercury) barometer reading, 40% relative humidity and 5000 feet altitude, the engine only produces about 81.1% of the rated horsepower. The dynamometer correction factor shown above is the reciprocal of the relative horsepower number. The dynamometer correction factor, the actual air pressure and the vapor pressure are included for comparisons to DynoJet chassis dynamometer test data.

There are also a myriad of other calculators available for different fuctions.

Now this is for Normal Aspirated Engines, but will give an idea of how temp/altitude/humidity come into play. I searched for a link for Forced Induction engines, but could not find one, anyone have a calculator for forced induction??
 

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Discussion Starter · #3 ·
SnowMan said:
Nope but FWIW, the NHRA uses 1/2 the NA functions for forced induction cars when correcting for altitude.
Excellant! Thanks for the info.
 
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