Thanks Mark,

This pretty much confirms what I have been thinking. It also confirms that Gustave Eiffel was a lot more clever that we thought

He has come up with a simple engine dyno that has a built-in power correction for density altitude. With paper, pencil and slide rule!

When I started this project, I didn't anticipate this move to higher grounds and wanted to use the test club predominantly as a relative measure for the improvements. Now I don't need to go back to a standard engine and start all over again

The humidity impact on power is pretty linear to the H2O vapour pressure (displaced O2) and is at our worst about 3-4% (25-30deg C and 100%). Here is a bit of an overview of different standards for ICE power correction factors:

Most use very similar formulae with only some minor changes in the influence factor for temperature and the reference air pressure and temp. None of them consider humidity as the influence is relativley small in the normal range of atmospheric conditions.

**DIN70020 Method**
This method for power correction, recommended by DIN70020 standard (DIN, 1986), does not account for changes in air humidity. If changes in the atmospheric conditions are small with respect to a standard condition, then the engine overall efficiency, fuel specific heat and air/fuel ratio can all be considered constants. Taking the engine volumetric efficiency varying proportionally to the square root of the temperature, the following correlation is written:

The DIN70020 method indicates the reference atmospheric condition of

*p0* = 1.01325 bar and

*T0* = 293 K.

**SAE J 1349 Method**
The SAE J 1349 standard (SAE, 1995) recommends the following atmospheric power correction factor (

*CF2*) for spark ignition engines:

The SAE J 1349 method indicates as a reference ambient condition for measuring the engine power in dynamometer tests

* p0* = 0.990 bar,

*T0* = 302.4 K, and

*p0*n = 0.013 bar. This correction factor is recommended to be applied in the range from 0.950 to 1.010 bar, and from 288.5 to 316.3 K.

**JIS D 1001 Method**
The JIS D 1001 standard (JIS, 1993) recommends the following correction factor (

*CF3*):

The reference atmospheric condition for Eq. (3) is of

*p0 *= 1013.25 mbar and

*T0* = 293 K.

**ISO 1585 Method**
This method is given by ISO 1585 standard (ISO, 1992), and is also adopted by the Brazilian Society of Technical Standards (ABNT, 1996). The suggested power correction factor (

*CF4*) is:

The reference ambient condition is

*p0* = 1.000 bar,

*T0* = 298K and

*p*n

*0* = 0.010 bar. The correction factor is recommended for utilisation in the range from 0.800 to 1.000 bar, and from 288 to 308K.