Variable Length Intake Manifold

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 (i.e., cross-sectional area), but the shorter and larger path opens when the load increases so that a greater amount of air can enter the chamber. In DOHC designs, the air paths are often connected to separate intake valves so the shorter path can be excluded by de-activating 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 - 2.8-liter V6 gas engine (1991-98); 3.6 and 4.2 liter V8 engines, 1987-present

* 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 and it was also found on the Yamaha V6 in the Taurus SHO.

* Ford - The Ford Modular V8 engines sport either the Intake Manifold Runner Control (IMRC) for 4V engines, or the Charge Motion Control Valve (CMCV) for 3V engines.

* General Motors - 3.9L LZ8/LZ9 V6, 3.2L LA3 V6

* GM Daewoo - DOHC versions of E-TEC II engines

* Honda - Integra, Legend, NSX, Prelude

* Hyundai - XG V6

* Jaguar - AJ-V6

* Lancia VIS

* Mazda VICS (Variable Intake Control System) is used in the Mazda B engine family of straight-4, and VRIS (Variable Resistance Induction System) 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 I4, V6, V8

* Opel (or Vauxhall) 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

* Proton - Campro CPS and VIM (still under testing)

* Renault - Clio 2.0RS

* Toyota T-VIS - (Toyota Variable Induction System) used in the early versions of the 3S-GE and 4A-GE families.

* Volkswagen - 1.6 L I4, VR6, W8

* Volvo - VVIS (Volvo Variable Induction System) Volvo_B52_engine as found on the Volvo_850 and S70/V70 vehicles, and their successors. Longer inlet ducts used between 1500 and 4100 RPM at 80% load or higher.