Engine Compartment Ventilation - Mercury MerCruiser Product Applications Manual

Air Intake System

Engine Compartment Ventilation

Adequate ventilation is required to properly evacuate the fumes from the engine
compartment and for proper engine operation. Insufficient ventilation will result in less than
optimum engine performance. This is of particular concern on boats with tight engine
compartments and those that use insulation to reduce engine noise. These techniques
restrict the flow of air and can trap heat, which significantly increases the susceptibility to
vapor locking.
IMPORTANT: This section does not cover the design of the ventilation system as it pertains
to ventilation of fumes from the engine compartment. The requirements for ventilation of
fumes varies considerably between boat designs and from country to country. Therefore,
the boat manufacturers are responsible for ensuring their application is in compliance with
the appropriate industry standards and regulations (Coast Guard, ABYC, NMMA, SAE
RCD, EU, ISO and others.)
1. The ventilation system must provide compliance with the specifications for maximum
pressure differential, fuel inlet temperature, and temperature at top of engine
compartment as defined under the engine compartment and fuel system pressure and
temperature test following.
2. The minimum air vent cross-sectional area shown in the following table can be used
as a starting point for sizing the system. Keep in mind that the air inlet requirements
can vary significantly from one boat design to the next, and that only performing the
following test ensures compliance with the ventilation requirements.
Ski Models
5.7L
350 MAG MPI
Black Scorpion
MX6.2L
MX 6.2 Black Scorpion
Inboard Models
5.7L
350 MAG MPI and 350
MAG MPI Horizon
MX6.2L
8.1S Horizon
8.1S HO
3. Ventilation openings must be increased if the boat is to be equipped with a generator
set.
4. On boats where more than one engine model is to be offered, size the ventilation
system for the largest horsepower offering.
5. Air vent cross-sectional specifications are for engine combustion air only and do not
consider the ventilation of fumes.
Page 4A-2
Ventilation System Specifications
Engine Air Requirements at
WOT
Model
3
m /sec. (ft
0.226 (486)
0.239 (506)
0.268 (567)
0.220 (466)
0.229 (486)
0.258 (545)
0.332 (660)
0.325 (689)
Minimum Air Vent
Cross-Sectional Area
Requirements (per Engine)
3
/min.)
2
cm
316 (49)
329 (51)
367 (57)
303 (47)
316 (49)
355 (55)
426 (66)
445 (69)
Engine Physical
Volume
L (ft
2
(in )
150 (5.3)
150 (5.3)
170 (6.0)
90-863758060 AUGUST 2006
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