Inlet manifold

An inlet manifold or intake manifold is the part of an <a href="/facts/Internal_combustion_engine/Ju4BXzj0">internal combustion engine</a> that supplies the <a href="/facts/Fuel/H8DIRL1j">fuel</a>/<a href="/facts/Air/hQ95Jznz">air</a> mixture to the <a href="/facts/Cylinder_(engine)/XlMRcfFl">cylinders</a>. The word <a href="/facts/Manifold_(engineering)/401KqWAN">manifold</a> comes from the Old English word manigfeald (from the Anglo-Saxon manig [many] and feald [repeatedly]) and refers to the multiplying of one (pipe) into many. 
In contrast, an <a href="/facts/Exhaust_manifold/SuHCw2pN">exhaust manifold</a> collects the <a href="/facts/Exhaust_gas/kLpq1eUX">exhaust gases</a> from multiple cylinders into a smaller number of pipes – often down to one pipe.
The primary function of the intake manifold is to evenly distribute the combustion mixture (or just air in a direct injection engine) to each intake port in the cylinder head(s). Even distribution is important to optimize the efficiency and performance of the engine. It may also serve as a mount for the carburetor, throttle body, fuel injectors and other components of the engine.
Due to the downward movement of the <a href="/facts/Piston/z7pN46u7">pistons</a> and the restriction caused by the throttle valve, in a reciprocating <a href="/facts/Spark_ignition/NATGwWSj">spark ignition</a> <a href="/facts/Piston_engine/ItLAxmW3">piston engine</a>, a partial <a href="/facts/Vacuum/BTk3goyV">vacuum</a> (lower than <a href="/facts/Atmospheric_pressure/wJLMSaVG">atmospheric pressure</a>) exists in the intake manifold. This <a href="/facts/Manifold_vacuum/pWQSD40u">manifold vacuum</a> can be substantial, and can be used as a source of <a href="/facts/Automobile_ancillary_power/ahEFPlDG">automobile ancillary power</a> to drive auxiliary systems: power assisted <a href="/facts/Brake/p8751fV6">brakes</a>, emission control devices, <a href="/facts/Cruise_control/qy0sUfjM">cruise control</a>, <a href="/facts/Ignition_system/7Rqqltpr">ignition</a> advance, <a href="/facts/Windshield_wiper/D6bsWc4l">windshield wipers</a>, <a href="/facts/Power_window/ImuPTqAR">power windows</a>, ventilation system valves, etc.
This vacuum can also be used to draw any piston blow-by gases from the engine's <a href="/facts/Crankcase/5Gb3fTHQ">crankcase</a>. This is known as a positive <a href="/facts/Crankcase_ventilation_system/rSRmUnW2">crankcase ventilation system</a>, in which the gases are burned with the fuel/air mixture.
The intake manifold has historically been manufactured from <a href="/facts/Aluminium/7wmR8jYE">aluminium</a> or cast iron, but use of composite plastic materials is gaining popularity (e.g. most Chrysler 4-cylinders, <a href="/facts/Ford_Zetec_engine/r34yMtf2">Ford Zetec</a> 2.0, Duratec 2.0 and 2.3, and GM's <a href="/facts/GM_Ecotec_engine/rLu5bVmW">Ecotec</a> series).

Inlet manifold open-in-new

Inlet manifold