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 system supplies a blast of air, like a tiny supercharger, into the combustion chamber under specific driving conditions. How sweet.

Tundra 5.7 engine cutaway photo

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, this rush of air 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 runners of different lengths. The truck’s ECM controls the position of the intake valve based on signals from the throttle angle and engine RPM. In effect, the ECM selections from the two lengths to tune the intake manifold. A pulse of high intake pressure is immediately available when the intake valve opens. The pulse pulls a large volume of air/fuel mixture into the combustion chamber. Another timely advantage is an improvement in fuel economy.

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.

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