Acoustic Control Induction System, or ACIS, is an implementation of a Variable Length Intake Manifold

Variable Length Intake Manifold

In internal combustion engines, a variable length intake manifold , or variable intake manifold is an automobile internal combustion engine manifold technology...

 system designed by Toyota.

Simply put, the ACIS system uses a single intake air control valve located in the intake to vary the length of the intake tract in order to optimize power and torque, as well as provide better fuel efficiency and reduce intake "roar"..

The engine control unit

Engine control unit

An engine control unit is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running...

 (ECU) controls the position of one or more air control valves based on input signals from throttle angle and engine RPM. The vacuum switching valve (VSV) which controls the vacuum supply to the actuator is normally closed and passes vacuum to the actuator when it is energized by the ECU. By energizing the VSV vacuum is passed to the actuator, closing the air control valve. This effectively lengthens the intake manifold run. By de-energizing the VSV, vacuum to the actuator is blocked and trapped vacuum is bled off of the actuator diaphragm. Toyota ACIS is an On/Off system. The valve (or valves in newer models with multiple valves to create more than 2 lengths) is either fully opened or fully closed.
An example of early single-valve ACIS programming would be the 3.0L 3VZ-FE engine. The ECU actuates the VSV to close the valve when the throttle position is 60% or greater and engine speed is 3,900 RPM or greater.

Applications:

• 3VZ-FE
  Toyota VZ engine
  The Toyota VZ engine family is a series of V6 gasoline piston engines ranging from 2.0L to 3.4L in displacement and both SOHC and DOHC configurations. The family introduced many changes for Toyota, including various EFI, ECU, and engine improvements from generation to generation. The VZ was...
  
  
• 1MZ-FE
  Toyota MZ engine
  The Toyota MZ engine family is a V6 piston engine series. The MZ series has an aluminium engine block and aluminium alloy DOHC cylinder heads. The cylinders are lined with cast iron, and is of a closed deck design . The engine is a 60 degree V6 design...
  
  
• 7M-GE
  Toyota M engine
  Toyota Motor Corporation's M family of engines were a longitudinally mounted straight-6 engine design. They were used from the 1960s through the 1990s. All M family engines were OHC designs. While the M family was born with a chain-driven single camshaft it evolved into a belt drive DOHC system...
  
  
• 2JZ-GE
  Toyota JZ engine
  The Toyota JZ engine family is a series of inline-6 automobile engines. A replacement for the M-series inline-6 engines, the JZ engines were 24-valve DOHC engines. The JZ engine was offered in 2.5 and 3.0 litre versions.-1JZ:...
  
  
• 1GZ-FE
  Toyota GZ engine
  The Toyota GZ engine family consists of a single model, the 1GZ-FE. This engine is used as the powerplant for the Japanese market-only Toyota Century limousine from 1997 onward.- 1GZ-FE :...
  
  
• 5E-FHE
  Toyota E engine
  The Toyota E engine family is a straight-4 piston engine series, using a timing belt rather than a chain. Like many other Toyota engines from the era, the E engine series features a cast iron block, along with an aluminum cylinder head. The members of the E engine family, range from 1.0 L to...
  
  

External links

• Lexus ACIS