AIR INLET AND EXHAUST SYSTEM
TESTING AND ADJUSTING
TM 5-3805-263-14&P-2
AIR INLET AND EXHAUST SYSTEM
RESTRICTION OF AIR INLET
ANDEXHAUST
There will be a reduction of horsepower and effi-
ciency of the engine if there is a restriction in the air
inlet or exhaust system.
Air flow through the air cleaner must not have a
restriction of more than 762 mm (30 in.) of water
difference in pressure.
Back pressure from the exhaust (pressure differ-
ence measurement between exhaust outlet elbow and
atmosphere) must not be more than 686 mm (27 in.)
of water.
MEASUREMENT OF PRESSURE
IN INLET MANIFOLD
By checking the pressure in the inlet manifold the
efficiency of an engine can be checked by making a
comparison with the information given in the FUEL
SETTING INFORMATION. This test is used
when there is a decrease of horsepower from the
engine, yet there is no real sign of a problem with the
engine.
The correct pressure for the inlet manifold is given
in the FUEL SETTING INFORMATION. Deve-
lopment of this information is done with these condi-
tions: 29.4 in. (746.7 mm) of mercury barometric
pressure, 85° F (29°C) outside air temperature and
35 API rated fuel. Any change from these conditions
can change the pressure in the inlet manifold. Out-
side air that has higher temperature and lower baro-
metric pressure than given above will cause a lower
horsepower and inlet manifold pressure measure-
ment, than given in the FUEL SETTING INFOR-
MATION. Outside air that has a lower temperature
and higher barometric pressure will cause a higher
horsepower
and
inlet
manifold
pressure
measurement.
A difference in fuel rating will also change horse-
power and the pressure in the inlet manifold. If the
fuel is rated above 35 API, pressure in the fuel inlet
manifold can be less than given in the FUEL SET-
TING INFORMATION. If the fuel is rated below
35 API, the pressure in the inlet manifold can be
more than given in the FUEL SETTING INFOR-
MATION. BE SURE THAT THE AIR INLET
AND EXHAUST DO NOT HAVE A RESTRIC-
TION WHEN MAKING A CHECK OF PRES-
SURE IN THE INLET MANIFOLD.
Use the 6V3150 Engine Pressure Group to check
the pressure in the inlet manifold.
This tool group has a gauge to read pressure in the
inlet manifold.
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