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Variable Length Intake Manifold (VLIM) is an centralized combustion engine manifold technology. Four common implementations exist. First, two discrete intake runners with different length are employed, and a butterfly valve can close the compendious path. Second the intake runners can be bent around a banal plenum, and a sliding valve separates them from the plenum with a variable length. Straight high-speed runners can receive plugs, which contain small long runner extensions.

As the exhaust gases equalize between the combustion chamber and the atmosphere, the difference in pressure decreases and the exhaust velocity decreases. This forms the medium-pressure chassis component of the exhaust pulse. The remaining exhaust gas forms the low-pressure tail component. This tail component may initially match ambient atmospheric pressure, but the momentum of the high- and medium- pressure components reduces the pressure in the combustion chamber to a lower-than-atmospheric level. The effect is known as scavenging. Length, cross-sectional area, and shaping of the exhaust Exhaust Systems ports and pipeworks influences the grade of scavenging effect, and the engine speed ambit over which scavenging occurs.