Variable length intake manifold

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Variable Length Intake Manifold (VLIM) is an automobile engine manifold technology. As the name implies, VLIM can vary the length of the intake tract in order to optimize power and torque, as well as provide better fuel efficiency.

There are two main effects of variable intake geometry:

Swirl - Variable geometry can create a beneficial air swirl pattern in the combustion chamber. The swirls help distribute the fuel and form a homogeneous air-fuel mixture which ignites without engine knocking. At low rpm, the speed of the airflow is increased by directing the air through a longer path with limited capacity, but the shorter and more capable path opens when the load increases so that the greater amount of air can enter the chamber. In DOHC designs, the air paths are often connected to a separate intake valves so the shorter path can be excluded by inactivating the intake valve itself.
Pressurization - A tuned intake path can have a light pressurizing effect similar to a low-pressure supercharger due to Helmholtz resonance. However, this effect occurs only over a narrow engine speed band. A variable intake can create two or more pressurized hot spots, increasing engine output.

Many automobile manufacturers use similar technology with different names. Another common term for this technology is Variable Resonance Induction System (VRIS).

Audi - 2.0 L I4, V6, V8
Alfa Romeo - 2.0 TwinSpark 16v - 155 ps(114 kW)
BMW DIVA
Ferrari - 360 Modena, 550 Maranello
Ford DSI (Dual-Stage Intake) - on their Duratec 2.5 and 3.0 liter V6s, 2.0 liter Zetec four, and it was also found on the Yamaha V6 in the Taurus SHO.
Ford - Variable intake geometry in the modular engined (after 1996) Mustang Cobra.
GM Daewoo - DOHC versions of E-TEC II engines
Honda - Integra, Legend, NSX, Prelude
Hyundai - XG V6
Jaguar - AJ-V6
Mazda VICS (Variable Intake Control System) is used in the Mazda B engine family of straight-4, and VRIS in the Mazda K engine family of V6 engines. An updated version of this technology is employed on the new Mazda Z engine, which is also used by Ford as the Duratec.
Mercedes-Benz
Mitsubishi Cyclone is used on the 2.0L I4 4G63 engine family.
Nissan V6 and V8
Opel TwinPort - modern versions of Ecotec Family 1 and Ecotec Family 0 straight-4 engines; a similar technology is used in 3.2 L 54° V6 engine
Peugeot 2.2 L I4, 3.0 L V6
Porsche VarioRam - 964, 993, 996, Boxster
Renault - Clio 2.0RS
Toyota T-VIS - (Toyota Variable Intake System) used on the 4A-GE family, notably in the MR2
Volkswagen - 1.6 L I4, VR6, W8

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