Editing Inlet manifold (section)

==Variable-length intake manifold==
{{main article|Variable-length intake manifold}}
[[Image:Lower-intake-manifold.jpg|thumb|right|Lower intake manifold on a 1999 Mazda Miata [[Mazda B engine#BP-4W|engine]], showing components of a variable length intake system.]]
A '''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 (physics)|power]] and [[torque]], as well as provide better [[fuel efficiency]].

There are two main effects of variable intake geometry:
* '''Venturi effect''': At low [[Revolutions per minute|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 [[Poppet valve|intake valves]] so the shorter path can be excluded by deactivating the intake valve itself.
* '''Pressurization''': A [[engine tuning|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''').
{{anchor |Vehicles using variable intake geometry|Vehicles}}
{{hidden begin
|title      = Vehicles using variable intake geometry
|titlestyle = background:#99FF99; text-align:left;
|bodystyle  = text-align:left;
}}
* [[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&nbsp;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]]: [[Ferrari 360 Modena|360 Modena]], [[Ferrari 550 Maranello|550 Maranello]]
* [[Ford Motor Company|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 Motor Corporation|Yamaha]] V6 in the [[Ford Taurus|Taurus SHO]]
*Ford: The [[Ford Modular engine|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 [[Ford CVH engine#2.0|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 [[GM High Value Engine|LZ8/LZ9]] V6, 3.2L [[GM 54-Degree V6 engine|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]]: [[Honda Integra|Integra]], [[Honda Legend|Legend]], [[Honda NSX|NSX]], [[Honda Prelude|Prelude]]
* [[Hyundai Motor Company|Hyundai]]: [[Hyundai XG|XG]] V6
* [[Isuzu]]: [[Isuzu Rodeo]], used in the second generation V6, 3.2L (6VD1) Rodeos
* [[Jaguar (car)|Jaguar]]: [[Jaguar AJ-V6 engine|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-4]]s, 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 [[Ford Duratec engine|Duratec]].
* [[Mercedes-Benz]]
* [[MG Motor|MG]]: [[MG ZS 180]] [[MG ZT]] 160, 180 and 190
* [[Mitsubishi]]: '''Cyclone''' is used on the 2.0L I4 [[Mitsubishi 4G63 engine|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 [[GM 54-Degree V6 engine|3.2&nbsp;L 54° V6]] engine
* [[Peugeot]]: 2.2&nbsp;L I4, 3.0&nbsp;L V6
* [[Porsche]]: '''VarioRam''' – [[Porsche 964|964]], [[Porsche 993|993]], [[Porsche 996|996]], [[Porsche Boxster|Boxster]]
* [[Proton (carmaker)|Proton]]: '''[[Campro engine#Campro CPS and VIM engine|Campro CPS and VIM]]''' – [[Proton Gen-2|Proton Gen-2 CPS]] and [[Proton Waja|Proton Waja CPS]]; Proton '''[[Campro engine#Campro IAFM engine|Campro IAFM]]''' – 2008 [[Proton Saga]] 1.3
* [[Renault]]: [[Renault Clio|Clio 2.0RS]]
* [[Rover (marque)|Rover]]: [[Rover 623]], [[Rover 825]], [[Rover 75]] v6,  [[Rover 45]] v6
* [[Subaru Legacy (first generation)#Engines|Subaru Legacy]] 1989–1994 [[Japanese Domestic Market|JDM]] EJ20 2.0-liter naturally aspirated DOHC 16-valve flat-4
* [[Subaru SVX#Engines|Subaru SVX]] 1992–1997 EG33 3.3-liter naturally aspirated DOHC 24-valve flat-6
* [[Subaru Legacy (third generation)#Engines|Subaru Legacy]] and [[Subaru Impreza#Engines|Subaru Impreza]] 1999–2001 [[Japanese Domestic Market|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 [[Toyota S engine#3S-GE|3S-GE]], [[Toyota M engine#7M-GE|7M-GE]], and [[Toyota 4A-GE|4A-GE]] engines, and '''[[Acoustic Control Induction System|ACIS]]''' (acoustic control induction system)
* [[Volkswagen]]: 1.6&nbsp;L I4, [[VR6]], [[W8 engine|W8]]
* [[Volvo]]: '''VVIS''' ('''Volvo variable induction system''') – [[Volvo Modular engine|Volvo B5254S and B5204S engines]] as found on the [[Volvo 850]] vehicles. Longer inlet ducts used between 1500 and 4100 rpm at 80% load or higher.<ref name=volvoclub>[http://www.volvoclub.org.uk/tech/850GLT-EngineTechInfo.pdf Volvoclub UK: 850GLT Engine Info]</ref>
{{hidden end}}