The Tundra’s Acoustically Controlled Induction System

Like the rose, a variable length intake manifold by any other name would still increase horsepower and torque. Toyota’s name for this technological rose, and the system used in all three Tundra engine options, is Acoustically Controlled Induction System. In the simplest terms, the ACIS supplies a blast of air, like a tiny supercharger, into the combustion chamber under specific driving conditions. How sweet.

Here’s a cutaway of the 5.7 V8. Note the tag for ACIS in the upper right hand corner.

ACIS goes a long way in providing consistent reservoirs of power and torque capable of rocket-like launches all across the power band. Anybody old enough to drive has experienced the same kind of “I had no horse” feeling experienced by Big Brown’s jockey in the Belmont Stakes. If Big Brown had been equipped with an equine version of ACIS, we’d have had a Triple Crown winner.

The Tundra’s ACIS is a two-stage system – other Toyota models, like the Lexus, have three-stage versions. At a certain engine speed, the airflow through the intake manifold naturally increases as a result of physical forces in the induction process. However, the rush of air from ACIS only occurs at one engine speed. The Tundra system uses a single intake valve to vary the length of the intake tract. The effect is similar to the technology used in late 90s Mustangs that used dual intake runners of different lengths, one of which was only open at lower RPMs. By using two runners, the intake manifold in the Mustang was essentially two different manifolds in one, with two different performance curves (both of which were optimized for a certain engine speed).

The Tundra’s ACIS system is a little better in that the ECM controls the position of the intake valve based on signals from the throttle angle and engine RPM. Because the computer can control when to open and close the “extra” intake runner, there is more control. When the extra runner is opened, a pulse of high intake pressure is immediately available. The pulse pulls a large volume of air/fuel mixture into the combustion chamber.

Another timely advantage of ACIS is an improvement in fuel economy. By tuning the air velocity, the Tundra’s ECM can optimize fuel-air mixing and improve the overall efficiency of the combustion chamber.

The ACIS is just the latest adaptation of the T-VIS (Toyota Variable Induction System) that kicks in at a set rpm while the latest version opens progressively, maintaining a constant powerband. Nearly ten years ago, one of the forerunners of the technology delivered added power to the ’96-’98 Mustang Cobra. Designed with two intake runners per cylinder, the system included a butterfly valve mounted between the intake and the heads. The longer runner delivered air to the cylinder up to 3200 rpms; at higher revs, the valve opened allowing an influx of air through both runners. Variations on this general theme, all with their own names and acronyms, now increase performance in a long list of engines including the Alfa Romeo, BMW, Mercedes, Ferrari and Porsche as well as the US’s Big Three.

Now, the next time you hear ACIS, you’ll know they’re talking about the intake manifold!

Related article: Stay Away From Throttle Body Spacers. With ACIS and comparable systems seen more and more, an old-fashioned spacer is a low-tech add-on that’s completely unnecessary. Steer clear.