TM 5-3805-258-24-1A I R I N L E T A N D E X H A U S T S Y S T EMT E S T I N G A N D A D J U S T I NGAIR INLET AND EXHAUST SYSTEMRESTRICTION OF AIR INLETAND EXHAUSTThere will be a reduction of horsepower and effi-ciency of the engine if there is a restriction in the airinlet or exhaust system.Air flow through the air cleaner must not have arestriction of more than 762 mm (30 in.) of waterdifference in pressure.Back pressure from the exhaust (pressure differ-ence measurement between exhaust outlet elbow andatmosphere) must not be more than 686 mm (27 in.)of water.MEASUREMENT OF PRESSUREIN INLET MANIFOLDBy checking the pressure in the inlet manifold theefficiency of an engine can be checked by making acomparison with the information given in the FUELSETTING INFORMATION. This test is usedwhen there is a decrease of horsepower from theengine, yet there is no real sign of a problem with theengine.The correct pressure for the inlet manifold is givenin the FUEL SETTING INFORMATION. Deve-lopment of this information is done with these condi-tions: 746.7 mm (29.4 in.) of mercury barometricpressure, 29°C (85°F) outside air temperature and35 API rated fuel. Any change from these conditionscan 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 lowerhorsepower and inlet manifold pressure measure-ment, than given in that FUEL SETTING INFOR-MATION. Outside air that has a lower temperatureand higher barometric pressure will cause a higherhorsepowerandinletmanifoldpressuremeasurement.A difference in fuel rating will also change horse-power and the pressure in the inlet manifold. If thefuel is rated above 35 API, pressure in the inletmanifold can be less than given in the FUEL SET-TING INFORMATION. If the fuel is rated below35 API, the pressure in the inlet manifold can bemore than given in the FUEL SETTING INFOR-MATION. BE SURE THAT THE AIR INLETAND 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 checkthe pressure in the inlet manifold.L O C A T I O N T O C H E C K I N L E T M A N I F O L D P R E S S U REA. Fitting.Remove fitting (A) on inlet air pipe to measureinlet manifold pressure.This tool group has a gauge to read pressure inthe inlet manifold. Special Instruction Form No.SEHS7851 is with the tool group and gives in-formation on the use of the group.6 V 3 1 5 0 E N G I N E P R E S S U R E G R O U P1 . D i f f e r e n t i a l p r e s s u r e g a u g e s . 2 . Z e r o a d j u s t m e ntscrew. 3. Pressure gauge 0 to 1100 kPa (0 to 160 psi). 4.Pressure tap. 5. Pressure gauge 0 to 415 kPa (0 to 60 psi).MEASUREMENT OF EXHAUSTTEMPERATURESUse the 1P3060 Pyrometer Group to check ex-haust temperature. Special Instruction Form No.SMHS7179 is with the tool group and gives instruc-tions for the test procedure.4-26.1/4-26.2 (blank)
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