Manifold vacuum
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Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere.
Autovac fuel lifters. On both buses the red Autovac tank can be seen above and behind the left front wheel.
Inlet manifold
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An inlet manifold or intake manifold is the part of an internal combustion engine that supplies the fuel/air mixture to the cylinders. The word manifold comes from the Old English word manigfeald and refers to the multiplying of one (pipe) into many.
Carburetors used as intake runners
Comparison of a stock intake manifold for a Volkswagen 1.8T engine (top) to a custom-built one used in competition (bottom). In the custom-built manifold, the runners to the intake ports on the cylinder head are much wider and more gently tapered. This difference improves the volumetric efficiency of the engine's fuel/air intake.
Lower intake manifold on a 1999 Mazda Miata engine, showing components of a variable length intake system.