Water Testing New Engines; Boat And Engine Performance; Boat Bottom - MerCruiser GM4 Service Manual

If engine exceeds the specified RPM, an increase in
pitch and/or diameter is required.
If engine is below rated RPM, a decrease in pitch and/
or diameter is required.
Normally, a change of approximately 300 to 500 RPM
will be achieved for each single pitch change of a pro-
peller.
! CAUTION
If a propeller is installed that does not allow en-
gine RPM to reach the specified full-throttle RPM
range, the engine will "labor" and will not pro-
duce full power. Operation under this condition
will cause excessive fuel consumption, engine
overheating and possible piston damage (due to
detonation). On the other hand, installation of a
propeller, that allows engine to run above the
specified RPM limit, will cause excessive wear on
internal engine parts which will lead to premature
engine failure.

Water Testing New Engines

Use care during the first 20 hours of operation on new
MerCruiser engines or possible engine failure may
occur. If a new engine has to be water-tested at full
throttle before the break-in period is complete, follow
this procedure.
1. Run boat up on plane.
2. Advance engine RPM (in 200 RPM increments)
until engine reaches its maximum rated RPM.
IMPORTANT: Do not run at maximum RPM for
more than 2 minutes.
Index
1A - 4 - GENERAL INFORMATION
Boat and Engine
Performance

Boat Bottom

For maximum speed, a boat bottom should be as flat
as possible in a fore-aft direction (longitudinally) for
approximately the last 5 ft. (1.5 m).
a - Critical Bottom Area
For best speed and minimum spray, the corner be-
tween the bottom and the transom should be
sharp.
a - Flat
b - Sharp Corner
72002
72003
90-816462 2-695