Acoustic Control Induction System

[Siriusly.Andrew]

It sounds super high tech, but the description Lexus has on the website is as follows;
"The engine uses high intake pressure pulses to pull an unusually high volume of air/fuel mixture into the combustion chamber, supercharging the engine and increasing torque."

http://www.lexus.com.bh/technology_e...del=All#active

I see this Acoustic Control Induction System on a lot of the Lexus IS series cars.

It makes me wonder how affective it is, and how it really works, as the Lexus IS250/C has a 2.5L V6 that produces 204hp @ 6400rpm, and 185lb-ft of torque @ 4800rpm. That is pretty underwhelming in my opinion.

What exactly is this "Acoustic Control Induction System" actually doing and what benefits does it bring? better economy? Just more torque? If so, how much torque does the engine gain as a product of this induction system?

Also have this, but I'm still not sure exactly what is happening to produce a "supercharged" like induction.

"Rather like an athlete, an engine performs better when it breathes more deeply. One way to increase the amount of air entering the engine is to optimise the length of the intake manifold. At a certain engine speed, the airflow through the intake manifold increases naturally as a result of physical forces at work in the induction process. The effect is a little like that of a supercharger. Normally, this extra rush of air happens at only one particular engine speed.

However, ACIS varies the length of the intake manifold in three stages, so you gain this natural, deep-breathing performance advantage across a broad range of engine revs."

[Midship Runabout]

So is this like a new TVIS system? Its pretty intersting the amount of design that goes into manifold designs, both intake and exhaust.

[Siriusly.Andrew]

I'm not sure yet. I've been looking at the picture for a while and it just looks like they have a "flap" that sits open to let air in normally, but splits it between combustion chamber and an extra length of intake manifold for "storage". Then when it wants that "Pulse" it closes outside intake and the air being stored gets forced into the combustion chamber giving it a charge? I don't know what gives it the "pulse" or force to call it charged intake though. Just seems like a higher volume air dump at certain engine speeds when its needed?

I edited the first post to include a link to the Lexus photo and description.


This is what Wikipedia told meh
"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""

[Snaps]

AFAIR (with regards to the Supra 2JZ-GE anyway) the ACIS is a little butterfly valve in the intake plenum Y-pipe. When it is closed (no air exchange between the two sides of the plenum) the plenum basically becomes 'longer', so the air velocity at low revs increases, creating slightly more torque. When at higher revs, the valve opens to allow either side of the plenum to take air from the other side (i.e. higher air volume), this also increases torque (and therefore power) at higher revs, when the air is already traveling fast and the restriction is in the amount of air the plenum can flow easily.

At least, that's how I understand it, which could be wrong

I would guess the Lexus version on newer cars is just a more advanced version of this which is made to create turbulent airflow at the right places and right times for more power/torque. Even though the given power levels are still pretty poor.... I think it's pretty well known that the (newer) IS series engines are pretty restricted with regards to exhaust and tuning.... But I have no backup for that.

[Midship Runabout]

Ah my phone is being gay and won't let me see the picture. From your discription it just sounds like a variable manifold runners activated by a butterfly valve that resticts air at lower rpm for more velocity and opens both runners up at a certain rpm to maximize flow. Much like the the tvis. Correct? If so its not really a new technology. My 3s motor has it as well as my old 94 SHO. (Both yamaha motors ) maybe dimman or someone with a little better understanding than me can chip in.

Edit: snaps beat me to it.

[70NYD]

Like snaps said. My 323 had that. Mazda called it vics. It just means that the runners can be short for high torque requirement and long for low torque requirements

[Dimman]

ACIS is a bit different than TVIS, but they are sort of similar.

ACIS is dealing with sound pressure waves to increase air into the motor, whereas TVIS is dealing with the inertia/speed of the intake air.

In inertial tuning, like TVIS, the diameter of the intake runner has an effect on the speed entering the combustion chamber (Bernoulli, venturi stuff, same amount of air entering a smaller area has to speed up). So smaller makes for faster intake air. But smaller has a limit to the amount of air that can go through it. So what TVIS does, is use a small runner to speed up the intake air (helps make torque), and opens up a second one at higher rpm, when it would start restricting power.

ACIS uses sound pressure waves for a similar purpose. It can actually create 'boost'. But the issue is how they do this. And it's also a bit mystical to me, so this may not be 100% on the ball, so bear with me.

Basically when the valves are suddenly opening and closing, the different pressure changes are making these 'pop' of pressure waves that move at the speed of sound up or down the intake (an exhaust) tract. Every time they meet a big pressure change, they 'pop' again and reverse direction. So they are bouncing back and forth down the intake or exhaust runners. This includes when one pulse from one cylinder goes up into the plenum, and the reaction pulse can be used by the other runners. So what ACIS is trying to do is time these pulses to 'stack up' and be creating positive pressure (boost) just as an intake valve is opening to cram in more air. However this is very rpm limited (this is what the short-runners=high rpm, long runners=low rpm comes from). How they time them and control them is by the lengths of the distance they travel before they reverse. What ACIS does is alters the length and/or volume that the sound pressure wave goes through, so that it takes more or less time, so that they can get it to optimize for more than one specific rpm range.

It gets even more complicated when valve overlap comes into effect, and the exhaust pressure waves actually fly up into the intake and can be used to enhance this even more. This is partly why super-high HP NA motors are peaky. Whereas the factory tunes these different effects to add torque/power in different areas to make a broad powerband. Performance tuning usually tunes them all for a specific, narrow rpm range that maximizes their effect on power.

Hope this helps. A bit.