Conditions That Lower Engine Performance - Mercury HP 500 EFI Bravo XR/XZ/III User Manual

CONDITIONS AFFECTING

Conditions That Lower Engine Performance

The following conditions lower engine performance and cannot be
compensated by the engine fuel or electronic management systems.
1. Above sea level elevations
2. High temperature.
3. Low barometric pressure.
4. High humidity.
These conditions (1 through 4 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 run 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 aspi-
rated and supercharged engines.
Compensating for power robbing conditions:
•
Switch to lower pitch propeller.
•
Change gear ratio.
Some boat performance can be regained 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.
500 EFI Bravo
OPERATION
71