1995 Johnson/Evinrude Outboards 40 thru 55 2-Cylinder Service Manual, Page 32Get this manual
Rated Power
Hot Weatherl High Altitude
Weather, Altitude, and Engine Performance
The horsepower ratings of all engines are those that would be obtained under standard conditionsHowever, changes in weather and altitude will affect the performance of any outboardSome factors that will decrease the output of an engine are: Low barometric pressure High temperature High humidity High altitude