Inlet Manifold - Variable Length Intake Manifold

Variable Length Intake Manifold (VLIM) is an internal 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 short path. Second the intake runners can be bent around a common 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. The plenum of a 6- or 8-cylinder engine can be parted into halves, with the even firing cylinders in one half and the odd firing cylinders in the other part. Both sub-plenums and the air intake are connected to an Y (sort of main plenum). The air oscillates between both sub-plenums, with a large pressure oscillation there, but a constant pressure at the main plenum. Each runner from a sub plenum to the main plenum can be changed in length. For V engines this can be implemented by parting a single large plenum at high engine speed by means of sliding valves into it when speed is reduced.

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:

• Venturi effect - At low rpm, the speed of the airflow is increased by directing the air through a path with limited capacity (cross-sectional area). The larger path opens when the load increases so that a greater amount of air can enter the chamber. In dual overhead cam (DOHC) designs, the air paths are often connected to separate intake valves so the shorter path can be excluded by deactivating 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 range which is directly influenced by intake length. A variable intake can create two or more pressurized "hot spots." When the intake air speed is higher, the dynamic pressure pushing the air (and/or mixture) inside the engine is increased. The dynamic pressure is proportional to the square of the inlet air speed, so by making the passage narrower or longer the speed/dynamic pressure is increased.

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 DISA and DIVA systems
• Dodge - 2.0 A588 - ECH (2001–2005) used in the 2001–2005 model year Dodge Neon R/T
• Ferrari - 360 Modena, 550 Maranello
• Ford VIS (Variable-resonance Intake System) - on their 2.9-liter 24V Cosworth (BOB) based on the Ford Cologne V6 engine in the later model Ford Scorpio.
• 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.
• Ford - The 2.0L Split Port engine in the Ford Escort and Mercury Tracer feature an Intake Manifold Runner Control variable geometry intake manifold.
• General Motors - 3.9L LZ8/LZ9 V6, 3.2L LA3 V6, and the 4.3L LF4 V6 in some second generation S10s and Sonomas
• GM Daewoo - DOHC versions of E-TEC II engines
• Holden - Alloytec
• Honda - Integra, Legend, NSX, Prelude
• Hyundai - XG V6
• Isuzu - Isuzu Rodeo Used in the second generation V6, 3.2L (6VD1) Rodeos.
• Jaguar - AJ-V6
• Lancia VIS
• Mazda VICS (Variable Inertia Charging System) is used on the Mazda FE-DOHC engine and Mazda B engine family of straight-4s, 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 - Proton Gen-2 CPS and Proton Waja CPS; Proton Campro IAFM - 2008 Proton Saga 1.3
• Renault - Clio 2.0RS
• Subaru Legacy 1989–1994 JDM EJ20 2.0-liter naturally aspirated DOHC 16-valve flat-4
• Subaru SVX 1992–1997 EG33 3.3-liter naturally aspirated DOHC 24-valve flat-6
• Subaru Legacy and Subaru Impreza1999–2001 JDM EJ20 2.0-liter naturally aspirated DOHC 16-valve flat-4
• Toyota T-VIS - (Toyota Variable Induction System) used in the early versions of the 3S-GE, 7M-GE, and 4A-GE engines, and ACIS - (Acoustic Control Induction System).
• 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.