Changing acis activation point??

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drunknmunky
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Changing acis activation point??

Post by drunknmunky »

As per title really, I'm wondering if it's possible to change the revs when the acis system kicks in, to much lower, like about 3 k ish? Thinking because it sounds beautiful when it's open, but I don't want to drive everywhere at 6 grand! And are there any disadvantage to doing it??
Thanks in advance people
shinny
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Re: Changing acis activation point??

Post by shinny »

Probably doable in a number of ways using aftermarket electronics... but there's no point, performance wise. People have done the analysis and it's already at the optimal point. Moving it either way results in less area under the graph.

This is different to Honda, who put the S2000's VTEC switchover deliberately late to give you that VTEC kick... which means Honda deliberately made the car slower to make it feel faster!
Last edited by shinny on Fri Nov 03, 2017 12:15 pm, edited 1 time in total.
drunknmunky
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Re: Changing acis activation point??

Post by drunknmunky »

Ok thanks pal, was thinking of just liberating intake decibels, but don't want to make it slower at all for sure.
I've already fitted a k&n cone to the original rubber pipework (just replaced air box with cone) but doesn't really give that intake roar I like so much.
shinny
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Re: Changing acis activation point??

Post by shinny »

drunknmunky wrote:Ok thanks pal, was thinking of just liberating intake decibels, but don't want to make it slower at all for sure.
I've already fitted a k&n cone to the original rubber pipework (just replaced air box with cone) but doesn't really give that intake roar I like so much.


You'll do better with noise if you take off the rubber pipework and resonator boxes and replace them with an alloy pipe.

See my howto video here:

Image
https://www.youtube.com/watch?v=LSv3XOiOFLo
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Driftlimits Performance
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Re: Changing acis activation point??

Post by Driftlimits Performance »

Resonator boxes on an NA do more than just reduce sound. I wouldn’t go tearing them off in a such a hurry.
jason256
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Re: Changing acis activation point??

Post by jason256 »

The sound is the whole engine coming into its tuned frequency, prematurely opening the ACIS wont make this noise happen at a lower RPM, it will just make you lose lower end power.
shinny
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Re: Changing acis activation point??

Post by shinny »

Driftlimits Performance wrote:Resonator boxes on an NA do more than just reduce sound. I wouldn’t go tearing them off in a such a hurry.


Go on...
pbmr2
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Re: Changing acis activation point??

Post by pbmr2 »

The resonators help the torque
drunknmunky
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Re: Changing acis activation point??

Post by drunknmunky »

Driftlimits Performance wrote:Resonator boxes on an NA do more than just reduce sound. I wouldn’t go tearing them off in a such a hurry.


I'm not questioning the answer, will believe people more knowledgeable than myself, but I'd be very interested in the physics behind this?? I like to know the how's and whys of what's best for the motor is all. Anyone got any links to post up for some bedtime reading??
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Driftlimits Performance
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Re: Changing acis activation point??

Post by Driftlimits Performance »

We do plan on doing some testing with our new NA airboxes with and without the resonators, and resonators of varying design.

Often fitting a straight pipe will increase mid range flat spots.

Search Helmholz resonator, it's much a likeness and do some reading. The theory makes sense but would like to see it in practice on a dyno.

Obviously you're not doing any harm without them, however for the perfect setup I believe there should be something on an NA.
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Re: Changing acis activation point??

Post by Driftlimits Performance »

Ok, here's something I pulled from Google....

Most hot-rodders and car enthusiasts think of intake resonators as simple mufflers in the intake tube, devices designed to siphon all the awesomeness out of a car's sound track to appease soccer moms and senior citizens. That makes it a prime candidate for the "chuck-it" school of auto modification. After all, it's basically just a plastic tumor growing off of a tube that should by definition be as smooth and blemish free as possible. While sound control is indeed part of the resonator's job, the sound control itself is really more of a side effect of its primary purpose.

Pressure Wave Harmonics

Air flowing into your cylinder head's intake port doesn't move in a straight line while the valve is open, then politely stop in its tracks to await another valve opening. When the valve closes, the moving column of air slams into it, then compresses and bounces back like a spring. This pressure wave travels backward at the speed of sound until the intake runner opens up or it hits something, and then it bounces back toward the cylinder. This is the "first harmonic." The pressure wave actually bounces back and forth two or three more times before the intake valve opens again.

Intake Tube Pulses

The resonator in your intake is technically known as a Helmholz resonator, an acoustic device used to control pressure wave harmonics. Air bouncing back out of your engine and into the intake tube doesn't do it in a single pulse the way it would in a single intake runner; the multiple pistons put out pressure waves at their own intervals, and some of those are going to try to bounce back in while others are going out. The result is a "clog" or high pressure area in your intake tube that ultimately limits airflow through almost the entire rpm spectrum.

The Resonator

Adding an expansion chamber to the intake tube forces air coming back out of the engine to slow down to fill the cavity, thus expending a great deal of its energy and slowing the pressure wave reversion. This slowdown allows fresh air to flow toward the engine without fighting pressure reversion waves the entire way, thus aiding in cylinder filling. Since these pressure waves are essentially sound, giving them a place to expend their energy before exiting the air filter box ends up dampening the intake noise and quieting the engine. Thus, the resonator helps to make the engine paradoxically quieter and more powerful.

shinny
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Re: Changing acis activation point??

Post by shinny »

Very interesting (and roughly the answer I was expecting). Still, I love the noise of the simple alloy pipe :whistle:
drunknmunky
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Re: Changing acis activation point??

Post by drunknmunky »

Thanks for that buddy, having read it it makes perfect sense now :-D now we just gotta figure out a way to liberate the decibels and get keep the power too then :-))
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