Humidity.

[Steve Webb]

Just a thought that came to me today, its well known that air temp and density has an effect on the way the engine performs and the amount of power it makes, but does humidity have a similar effect?
Logic dictates that the extra water in high humidity air will act as a (very weak) form of water injection.
Anyone else have any thoughts on this, or links to actual tests of the theory?

[the wombat]

Just taken a look on the interweb thingy, and the consensus seems that high humidity can reduce power as the water displaces the oxygen in the charge.

Water injection helps cool the charge making it denser, but also help reduce knock so that timing can be advanced further.

Not something I have a lot of knowledge in, but the interweb seems to have some good info.

Dense cold dry air seems to be the optimum.

[mpampis_]

There is something else. Water is cooling the air too in the cylinders. Colder air means same amount of air with less volume so in higher boost there you can put more air- fuel mixture in the cylinder so more power

[Steve Webb]

One thing that I forgot was that as air gets colder its ability to hold water decreases, so you will never have cold humid air.
So I guess the its more a case of a hot humid day would be better than a hot dry day, but nowhere near as good as a cold day.

I suppose one problem with high humidity would be condensation within the inlet tract.

[mpampis_]

Best performances I saw in my car at 6-7 C. Turboweather