Air Box Pressure
Proper air box pressure is required to maintain
sufficient air for combustion and scavenging of the
burned gases. Low air box pressure is caused by a high
air inlet restriction, damaged blower rotors, an air leak
from the air box (such as a leaking end plate gasket),
or a clogged blower air inlet screen.
Lack of power or black or grey exhaust smoke are
indications of low air box pressure.
To check the air box pressure, connect a manometer to
an air box drain tube.
Check the readings obtained at various speeds with the
specifications in Table 5.
Air Inlet Restriction
Excessive restriction of the air inlet will affect the flow
of air to the cylinders and result in poor combustion
and lack of power. Consequently, the restriction must
be kept to a minimum considering the size and
capacity of the air cleaner. An obstruction in the air
inlet system or dirty or damaged air cleaners will
result in a high blower inlet restriction.
The air inlet restriction may be checked with a
manometer connected to a fitting in the air intake
ducting located 2" above the air inlet housing. When
*Engines with four valve cylinder heads.
practicability prevents the insertion of a fitting at this
point, the manometer may be connected to the engine
air inlet housing. The restriction at this point should
be checked at a specific engine speed. Then the air
cleaner and ducting should be removed from the air
inlet housing and the engine again operated at the
same speed while noting the manometer reading.
in the exhaust manifold companion flange and
tapping a 1/8" pipe thread.
The difference between the two readings, with and
without the air cleaner and ducting, is the actual
Check the readings obtained at various speeds (no
restriction caused by the air cleaner and ducting.
load) with the specifications in Table 4.
Check the normal air intake vacuum at various speeds
(at no-load) and compare the results with Table 6.