Acoustic Control Induction System -- ACIS--
There are a lot of people that haven't a clue what ACIS is or what it does. So, i did some research at work using our Toyota Technical Information System (TIS) and i dug up some technical training for the ACIS system. I then took that published information and created a webpage with text, diagrams and pictures. There is a wealth of information out there, the trouble is finding it. So i will do my best to describe the system, its operation, and the role it plays in performance.
http://www.geocities.com/mwsupra2003/acis.html
the above link has all of the information below. please goto the link for helpful diagrams and pictures. 
---Theory----
Using laws of inertia, thermodynamics and physics the toyota engineers discovered that the opening and closing of the intake valves creates acoustic energy pulses that bounce around inside the intake manifold and chamber. They then developed a system, called ACIS, to control and manipulate those acoustic pulses to create a "supercharging" effect.
By varying the length of the intake runners through the use of valves, the toyota engineers found a way to time the acoustic pulses so they enter the cylinders through the intake valves. This means that after an intake valve closes and creates this acoustic pulse, the pulse bounces off the intake runner and chamber and then is timed to enter at the next intake cycle so the valve is opened with a pressurized acoustic wave being forced into the cylinder.
---Application---
Toyota has many NA engines that utilize the ACIS system. (7m-ge, 2jz-ge, 2jz-fe, 1mz-fe, ect, ect) In our case, the 7mge, there is a butterfly valve (intake air control valve(IAC)) placed in the middle of our intake manifold behind the union of the Y-pipe. This valve is controlled by an ACIS actuator. The Actuator is controlled via vacuum provided by the either the throttle, VSV's or the ECM ( or all three). There is a vacuum storage tank located beneath the intake manifold and that is connected to a port near the Intake air control valve.
---Operation---
I'm not sure on the switchover throttle position for the 7mge, but the activation RPM is 4200. Before that point at WOT, the Air control valve is closed, meaning that the cylinders are getting shared air from just behind the throttle body. This means that the engine is utilizing long intake runners. Under WOT, past 4200 rpms, the air control valve is opened and the cylinders are now getting shared air from the center of the intake manifold, meaning the engine now has shortened intake runners. ( see diagram on site)
On the 2JZ-FE engine, there is an activation rpm of 4,500 and a 30% throttle crossover map. meaning....
low throttle... ( less than 30%)
<4500 rpm = valve open ( short runners )
>4500 rpm = valve close ( long runners )
high throttle... ( more than 30%)
<4500 rpm = valve close ( long runners )
>4500 rpm = valve open (short runners )
This system ( two stage acis) essentially gives you two torque curves. The valve is timed to open on the downfall after the first peak, so the engine has potential to make equal or more power later on throught the power band.
--- Modification ---
Modifying the ACIS system is not recommended because it has been tuned for the specific engine. But the thought does provoke interest. If by changing the activation RPM and/or throttle %, could you tune where you want your torque to peak?
I have the ACIS system on my now turbocharged 7M-GE and remarkebly it has still provided two torque curves between the designated 4200rpm. I plan to do some experimentation with ACIS during my next trip to the dyno. I will perform runs with the valve closed ( long runners), with the valve open ( short) and then multiple runs using different activation RPMS. If this system can yield more power because of its changing attributes, then it may be a desired modification for mid-power performance enthusiasts.
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