Effects Of Elevation And Weather On Performance - Mercury Racing 500R Operation And Maintenance Manual

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:
• Boost pressure on supercharged engines
• 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.
The 500R outboard is equipped with a humidity sensor in the intake tract which
will compensate for changes in humidity.
Compensating for power robbing conditions:
• Switch to lower pitch propeller.
• Change gear ratio (if available).
Some boat performance can be improved by dropping to a lower pitch
propeller, but engine performance will still remain lower. In some cases, a gear
ratio reduction may be more beneficial. 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 or gear ratio changes:
• Reduces the possibility of detonation
• Enhances overall reliability and durability of the engine
eng
OPERATION
73