Indmar Marine Engines
4-9
Load, weather, altitude and boat condition all affect
WOT engine operation. If you use your boat for several
different applications such as wakeboarding, barefooting
and cruising, it may be necessary to have 2 or more pro-
pellers which will allow the engine to operate in the WOT
range for each application.
Propping the boat should be done after engine break-in
and the initial 10 hour dealer check. The boat should be
loaded the way it would normally be for each application.
For instance, if you are propping for wakeboarding, fill
the ballast tanks if equipped and add all the people and
gear you would normally expect to carry in the boat.
Take the boat out and after warm-up, run it at wide-open-
throttle and note the maximum RPM. EFI Engines are
equipped with RPM limiters to prevent over-revving.
If the WOT RPM is higher than the maximum RPM in
your engine’s WOT operating range, the boat is under-
propped. Install a higher pitched propeller to reduce
WOT RPMs. An engine that is over-revving may quickly
experience catastrophic damage.
If the WOT RPM is lower than the minimum RPM in your
engine’s WOT operating range, the boat is over-propped.
Install a lower pitched propeller to increase WOT RPMs.
An engine that is under-revving is lugging. Lugging
places tremendous loads on the pistons, crankshaft and
bearings and can cause detonation, piston seizure and
other engine damage.
Elevation and weather also have a very noticeable effect
on the wide-open-throttle power of an engine. Since air
(containing oxygen) gets thinner as elevation increases,
the engine begins to starve for air. Humidity, barometric
pressure and temperature have a noticeable effect on
the density of air since heat and humidity thin the air.
This phenomenon can become particularly apparent
when an engine is propped out on a cool dry day in
spring and later, on a hot, humid day in summer, does
not have the same performance. Although some per-
formance can be regained by dropping to a lower pitch
propeller, the basic condition still exists. The propeller is
too large in diameter for the reduced power output. An
experienced marine dealer can determine how much
diameter to remove from a lower-pitch propeller for spe-
cific high-elevation locations.
Indmar suggests that if you do require a different pro-
peller, consult the dealer you bought the boat from. The
dealer is best equipped to help with the selection of the
correct propeller for your application(s).
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Summary of Contents for 5.7L MPI
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