Effects of Elevation and Weather on Performance
The following conditions lower engine performance and cannot be
compensated by the engine fuel or electronic management systems:
• Above sea level elevations
• High temperature
• Low barometric pressure
• High humidity
These conditions above reduce air density to the engine, which in turn lowers
the following:
• Horsepower and torque throughout the RPM range
• Peak RPM
• Cranking compression
EXAMPLE: An engine running at an elevation of 8,000 feet will have over a
30% power loss while a loss of engine power on a hot and humid day could be
as much as 14%. These losses apply to normally aspirated and supercharged
engines.
Compensating for power robbing conditions:
• Switch to lower pitch propellers.
Some boat performance can be improved by dropping to lower pitch propellers,
but engine performance will still remain lower. To optimize engine performance,
prop the engine to allow it to operate at or near the top end of the
recommended maximum RPM range at wide‑open throttle with a normal boat
load.
Other advantages to propeller changes:
• Reduces the possibility of detonation
• Enhances overall reliability and durability of the engine
OPERATION
eng 61
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