TM 5-3895-383-24
Air Inlet And Exhaust System
Restriction Of Air Inlet And Exhaust
There will be a reduction of horsepower and efficiency 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
(negative
pressure
difference
measurement
between
atmospheric air and air that has gone through air cleaner) of
more than 635 mm (25 in) of water.
Back pressure from the exhaust (pressure difference
measurement
between
exhaust
at
outlet
elbow
and
atmospheric air) must not be more than 1016 mm (40 in) of
water.
Maximum Exhaust Back Pressure Specifications.
Standard Muffler...............................686 mm (27 in) of water
Water Cooled Exhaust..................1016 mm (40 in) of water
Measurement Of Pressure In Inlet
Manifold
Tools Needed
1U5470
Engine Pressure Group
1
8J7844
Adapter (3/4-16 to 1/4 NPTF)
1
3K0360
O-ring Seal
1
4M5317
Reducing Bushing (1/4 NPTF to 1/8 NPTF)
1
The efficiency of an engine can be checked by making a
comparison of the pressure in the inlet manifold with the
specifications
given
in
the
TMI
(Technical
Marketing
Information) Governor Bench Performance Data. 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.
Development of this information is done with these conditions:
1.
737 mm (29 in) of mercury barometric pressure (dry).
2.
29C (85F) outside air temperature.
3.
35 API rated fuel.
Any change from these conditions can change the pressure in
the inlet manifold. Outside air that has higher temperature and
lower barometric pressure than given above will cause a lower
horsepower and a lower inlet manifold pressure measurement
than given in the TMI. Outside air that has a lower
temperature and a higher barometric pressure will cause
higher horsepower and a higher inlet manifold pressure
measurement.
A difference in fuel API rating will also change horsepower and
the pressure in the inlet manifold. If the fuel is rated above 35
API, pressure in the inlet manifold can be less than given in the
TMI. If the fuel is rated below 35 API, the pressure in the inlet
manifold can be more than given in the TMI. Fuel API rating
can be easily checked using the 1P7408 Thermo-Hydrometer.
Instructions are given in Special instruction GMGO0977-02.
BE SURE THAT THE AIR INLET OR EXHAUST DOES NOT
HAVE A RESTRICTION WHEN MAKING A CHECK OF
PRESSURE IN THE INLET MANIFOLD.
1U5470 Engine Pressure Group
To check the inlet manifold pressure, remove one of the plugs
(1) on top of inlet manifold. Connect the adapter, seal,
reducing bushing, and 1U5470 Engine Pressure Group to this
opening.
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