GASOLINE ENGINES SKI MODELS
Page 7 of 48
Over the last several years, engine compartments have been designed to be quieter. The
most common material used to deaden the engine sound is some type of insulation material.
Normally, the quieter the engine compartment is, the more insulation material used, which
results in less air space inside. The less air space inside the engine compartment, the hotter
the inside air temperature. Attention must be given to the air temperature that is inside this
engine compartment while the engine is running or after a period of time after the engine
is shut off (heat soak). Refer to the following information on Engine Compartment
Ventilation.
ENGINE COMPARTMENT VENTILATION
General Information
According to Boating standards (NMMA, ABYC, etc.) and Coast Guard regulations the en-
gine compartment ventilation system has multiple tasks. Included are the following:
1. To supply the engine with combustion air.
2. To maintain a low temperature in the engine compartment.
Fresh air should enter the engine compartment as low as possible and the heated air should
be discharged from the highest point.
When sufficient ventilation is not provided, too much heat can build-up inside of engine
compartment and cause vapor locking. The engine will not want to restart after it has been
shut off for a short period of time. If it does restart, the engine will quit when given the throttle
to get the boat up on plane or to pull up a water skier.
For engines utilizing fuels containing alcohol and the newer “reformulated gasolines” (See
OEM Service Bulletin 95-2), proper ventilation is more critical to prevent vapor locking.
If a separate air shaft (or similar) is used to provide engine compartment ventilation or addi-
tional ventilation, care must be taken to prevent seawater and spray from entering it.
Combustion Air Requirements
Engine compartments with natural draft ventilation must have vent openings of sufficient
size and location to accomplish the tasks previously outlined.
IMPORTANT: The size of ventilation openings must be increased if any auxiliary
equipment is located in the engine compartment.
The combustion air requirement (per engine) for the specified engines at Wide Open
Throttle are given in the chart below:
Engine Air Flow Requirements (Per Engine)
Model
Engine Air Requirements at
Wide Open Throttle
Physical
Volume
5.7L
486 ft.
3
/Min.
(0.229 m
3
/sec.)
5.3 ft.
3
(150 L)
350 Mag MPI
506 ft.
3
/Min.
(0.239 m
3
/sec.)
5.3 ft.
3
(150 L)
MX 6.2L MPI
568 ft
3/
Min.
(0.268 m
3
/sec.)
5.3 ft.
3
(150 L)
Black Scorpion
527 ft.
3
/Min.
(0.249 m
3
/sec.)
5.3 ft.
3
(150 L)
In addition, the pressure differential (outside engine compartment versus inside engine
compartment) should not exceed 2 in. (51mm) of water (measured with a manometer) at
Wide Open Throttle.