Muffler - The function of a Muffler or a Silencer in Vehicle is to cool the exhaust gases by expansion through it and to reduce the noise of outgoing gases.The exhaust gases must be discharged into the atmosphere with minimum restriction.The restriction in flow of exhaust gases causes back pressure.Back pressure on piston head during exhaust stroke due to restriction of flow of exhaust gases.It is generally 0.7 - 0.9 Kg/cm2 at maximum rpm.The back pressure at low value by proper designing of exhaust system.High back pressure results in higher bhp loss at particular speed, Dilution of fresh charge with exhaust gases, Increased fuel consumption.Back pressure can be reduced by proper design which may become bulky and costly.The exhaust manifold are made of cast iron or steel.Bend should be such made as to give minimum restriction.Muffler design have internal baffles which restrict the flow of gases and cause back pressure.It reduce noise effectively with more rise in back pressure.

The last specified function is the function of the car muffler.It is necessary because the gas coming from the combustion in the pistons of the engine would generate an extremely loud noise if it were sent directly in the ambient surrounding through the exhaust valves.