acis system?

[critical-audio]

anyone know anything about the acis system, did a quick search but didn't find anything. i remember reading something about a little PnP on it but my buddy has an s-er altima and their system is called the vias. he keeps bugging me saying to delete it and just put a plate on the side of the plenum. link shows some info

http://www.nissanclub.com/forums/200...-opinions.html

was curious what peoples thoughts were on this

[Gothmog3VZ]

posting from psp so i'll put link later, but its essentially a flap to alter the length of the intake runners. you just round off the edges of the housing. hard to explain without pics...

[2wickedtoyz]

Originally Posted by critical-audio

anyone know anything about the acis system, did a quick search but didn't find anything. i remember reading something about a little PnP on it but my buddy has an s-er altima and their system is called the vias. he keeps bugging me saying to delete it and just put a plate on the side of the plenum. link shows some info

http://www.nissanclub.com/forums/200...-opinions.html

was curious what peoples thoughts were on this

it's stickied on top of every forum section

Camry FAQ ------> READ FIRST -----> Comprehensive List of Gen 3/4 INFO and DIY

http://www.toyotanation.com/forum/t45066.html

[Jason.MZW20]

Originally Posted by critical-audio

he keeps bugging me saying to delete it and just put a plate on the side of the plenum. link shows some info

Well don't listen to him. ACIS operates on the theory of Helmholtz Resonance.

Originally Posted by Wikipedia

When air is forced into a cavity, the pressure inside increases. When the external force pushing the air into the cavity is removed, the higher-pressure air inside will flow out. However, this surge of air flowing out will tend to over-compensate, due to the inertia of the air in the neck, and the cavity will be left at a pressure slightly lower than the outside, causing air to be drawn back in. This process repeats with the magnitude of the pressure changes decreasing each time.

The pressurization effect only occurs over a short RPM range, which is why the runners are tuned and the ACIS system activates at a certain RPM. You can see the ACIS system working in 3VZ or 1MZ dynos. The curves dip a bit as the pressure in the manifold drops, then immediately pressurizes and gains inertia creating more power. It gives the V6s double torque peaks, where one peak is at around 3500rpm and is about 95% of peak torque, while the next torque peak occurs at 4400rpm with the short runners activated and is 100% of peak torque the engine produces.

The effect would be better with higher lift camshafts, like the 2MZ's cams in the 1MZ. Here's a 1MZ (no VVT-i, manual trans) dyno plot:



After about 3500rpm, the longer runners start to lose steam, then at 3700rpm the ECU activates the shorter runners and the curves build up again.

The 3-stage ACIS system on the early VVT-i 1MZs aimed to remove the middle dip and improve mid-range torque.

[Silent Runner]

Thanks for posting this dyno graph! It really shows what the ACIS system does. for a tiny blip in the hp curve it holds up a big flat and strong torque number. How an engine performs and really pushes a car along is a combination of these characteristics. Old super special factory race cars had induction systems with specialized long or short intake runners, (for high end power or low end torque), this engine/ car does both to max out real daily performance. I would never disable it unless my other engine mods overan its effects. A big high flat torque curve, + a nice steady climbing power (hp) curve. Thats about as good as it gets without variable valve timing and lift.

[critical-audio]

ya wicked i knew i read something somewhere about porting and polishing, but hes saying to totally remove it and put over the side of the plenum to delete that little butterfly valve which wouldn't it make it so all the intake runners got air instead of just the top ones until it opened up? does it alter the length of the runners or does it alter how many runners have air flowing? i mean im sure if toyota engineers put it in there they did for a reason, but im just curious what this would do from a performance stand point, loss in some torque for more top end hp?

[Jason.MZW20]

Originally Posted by critical-audio

ya wicked i knew i read something somewhere about porting and polishing, but hes saying to totally remove it and put over the side of the plenum to delete that little butterfly valve which wouldn't it make it so all the intake runners got air instead of just the top ones until it opened up? does it alter the length of the runners or does it alter how many runners have air flowing? i mean im sure if toyota engineers put it in there they did for a reason, but im just curious what this would do from a performance stand point, loss in some torque for more top end hp?

If you removed just the butterfly valve and didn't block the hole, you'd have the long runners active permanently. As the dyno graph shows, the long runners lose torque after 3500rpm, so you'd lose torque and, subsequently, HP. If you completely blocked off the top portion of the intake manifold by sealing the butterfly valve shut, you'd have the short runners active at all times. Dynos have been done, and you lose low-end torque/HP.

It's best to leave the ACIS system as-is. The TRD supercharger deletes the ACIS system, but in its place you get rotors to compress the air.