[455firebird1969]

Originally Posted by Elarson

Humidity displaces oxygen. Think of it this way. Every water molecule in the air going into your engine takes the place of a useful oxygen molecule that would have otherwise gone in.

Rain isn't the culprit directly, but a rainy day has high humidity.

Eric

My initial point was rain is not water vapor. (Mike said he did it in the rain). Water vapor affects density altitude (which affects performance), rain does not. Rain is the result of atmospheric conditions. If he had stated he did it in low pressure air or poor conditions, I would not have provided input. My point is cold air cannot hold as much water vapor when compared to warm or hot air. Simply because it is raining, does not necessarily mean you have a high water vapor content. High humidity does not indicate high water vapor content. If the air is cold, things change. Saying a rainy day has high humidity is vague unless you include the tempurature.

The psychometric chart indicates 50 f. air / at 90% humidity holds 49 grains per pound water vapor.
While, 90 f. air / at 70% humidity holds 150 grains per pound of water vapor.

37 f. air with 100% humidity can only hold 33 grains per pound.

Mikes performance is stellar, and I congratulated him, it's not about his achievements.

All I'm trying to do is help those reading this to understand how meteorology works.