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Thread: Don't buy/build an intake, just remove the resonator/snorkel tube

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    Senior Member GrnBn's Avatar
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    Don't buy/build an intake, just remove the resonator/snorkel tube

    I recently changed my engine air filter and spark plugs, and while doing so you must necessarily remove the air intake box to access the Coil-On-Plugs and the plugs themselves. This is all incredibly straight-forward stuff, and so I'm not here to give a write-up on doing that unless people are really keen on getting one. What I am here to talk about is the Mirage air intake assembly. I want to confirm what some other users have said regarding removal of the intake resonator/snorkel tube, and also to suggest some alternative ideas about what is going on with these removed.


    The main airbox(where your filter sits) has two attached pieces hanging off the left side which are loosely integrated together. These are a box-like resonator compartment -that actually sticks back into the filter chamber- and the oval-shaped snorkel-looking tube that connects to both the resonator box and the main air intake chamber. To my topical point, anyone trying to get a more sporty intake sound and/or mild performance gains should remove these pieces from their intake assembly. After removing these components from my own car, I think this is an easy first step for people who want to get a bit more out of their Mirage without wasting money on dubious pipes and filters.

    I notice there are several things happening when you remove these two pieces. First and foremost among them is that your engine is getting more air, more easily, than it previously did. This is most noticeable in the higher RPMs, when the MIVEC system engages the more aggressive cam profile. There is also substantially more intake/engine noise when this occurs, but it is surprisingly deep sounding and for those after a more sporty driving experience you will not be disappointed. The car pulls more easily to high RPMs, and sounds less strained in doing so.

    The flip side of this increased breathing capacity, however, is that your intuitive feel of the throttle pedal is no longer correct, and must be re-learned if you don't want to drive your fuel economy numbers down into the 30s or perhaps even high 20s. The car breathes better -albeit more loudly- without these components, and if you're not attentive you'll be over-throttling it everywhere. In fact, this is what I think others have described as a sensation of lost torque at low RPMs. I think that, rather than there being any appreciable torque dip, what others are describing is their car bogging under an overly rich air/fuel mixture and gearing combination. When I want to get good fuel economy I drive gently and coast when I'm able, and I still regularly get mid-40s MPG even without the two pieces mentioned above.

    I encourage anyone with a 10mm socket and some curiosity to try removing these pieces for themselves. The car will run just as good as it did with them attached, and you may find you like the MIVEC noises.



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    Moderator Eggman's Avatar
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    Quote Originally Posted by GrnBn View Post
    To my topical point, anyone trying to get a more sporty intake sound and/or mild performance gains should remove these pieces from their intake assembly. After removing these components from my own car, I think this is an easy first step for people who want to get a bit more out of their Mirage without wasting money on dubious pipes and filters.

    I notice there are several things happening when you remove these two pieces. First and foremost among them is that your engine is getting more air, more easily, than it previously did. This is most noticeable in the higher RPMs, when the MIVEC system engages the more aggressive cam profile. There is also substantially more intake/engine noise when this occurs, but it is surprisingly deep sounding and for those after a more sporty driving experience you will not be disappointed. The car pulls more easily to high RPMs, and sounds less strained in doing so.

    The flip side of this increased breathing capacity, however, is that your intuitive feel of the throttle pedal is no longer correct, and must be re-learned if you don't want to drive your fuel economy numbers down into the 30s or perhaps even high 20s. The car breathes better -albeit more loudly- without these components, and if you're not attentive you'll be over-throttling it everywhere. In fact, this is what I think others have described as a sensation of lost torque at low RPMs. I think that, rather than there being any appreciable torque dip, what others are describing is their car bogging under an overly rich air/fuel mixture and gearing combination. When I want to get good fuel economy I drive gently and coast when I'm able, and I still regularly get mid-40s MPG even without the two pieces mentioned above.

    I encourage anyone with a 10mm socket and some curiosity to try removing these pieces for themselves. The car will run just as good as it did with them attached, and you may find you like the MIVEC noises.
    Well, you make some good points particularly about sound but just to be clear the resonator does have a functional effect. It has been discussed on other intake modification threads here:

    DRIFT Xaust air intake system on Mitsubishi Mirage
    Warm Air Intake - Intercooler as an intake heater
    DIY: Warm Air Intake – Air box tube to exhaust manifold

    I ran without my resonator and can vouch that I perceived no increase in performance. Regarding running 'better' - without dyno measurements, it's only a guess. It was noisier.



    Here's some further reading on intake resonators.

    Reference.com: What Is an Air Intake Resonator?
    Quote Originally Posted by Reference.com: What Is an Air Intake Resonator?
    The air intake resonator is simply an expansion chamber, a wide spot within a car's intake pipe. Resonators come in two types: in-line resonators, which are open chambers fitted in the intake tube, and side branch resonators, which are chambers that sit next to the intake tube and are connected to it via a small channel or duct.

    A common misconception among many auto enthusiasts and hot-rodders is that the air intake resonator is there for the sole purpose of muffling the sound of the engine on an older car. While dampening the sound of the engine is one of the purposes of the air intake resonator, it is not the primary purpose. The primary purpose of the air intake resonator is to inhibit pressure wave harmonics, which causes air pressure in the engine and restricts the amount of airflow through the RPM spectrum. In effect, the air intake resonator, via its expansion chamber, slows down the air emerging from the engine. This reduces the engine intake noise and increases the amount of horsepower available.

    Brighthubengineering.com: How Intake Resonators improve Volumetric Efficiency

    Quote Originally Posted by Brighthubengineering.com: How Intake Resonators improve Volumetric Efficiency
    The intake manifolds of modern naturally aspirated IC engines are integrated with resonators. The purpose of the Helmholtz resonator is to improve the volumetric efficiency of the engine and also to help with engine sound attenuation. This is possible due to the special features of the Helmholtz resonator designs.

    ItStillRuns.com: What Does an Air Intake Resonator Do? by Richard Rowe

    Quote Originally Posted by ItStillRuns.com: What Does an Air Intake Resonator Do? by Richard Rowe
    The Common Misconception
    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.
    Unless I misunderstand, changing one part of the whole might not bring about the improvements expected. As with many modifications: change one thing, affect ten others. In order to allow more air in - ostensibly for 'better breathability' - I understand it is important to address the entire path of airflow in and exhaust flow out.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.6 mpg (Imp)


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    Maybe I'm wrong but I thought the air/fuel mixture was regulated by a feedback loop from the oxygen sensors?

    And if you decide to run without the resonator in place, be sure to replace that little bolt with the 10mm hex head or oil will splash out of that hole.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.6 mpg (Imp)


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    I'm assuming it's this piece (highlighted)? I have done that 'mod' before but I didn't see/feel any improvements with acceleration. If anything, it was just the intake getting louder. But that's about it. It 'felt' like I lost more low-end power; stop and go acceleration was just took a 'bit' more gas to make it go. I didn't see any improvements with gas mileage though. Free mod for sure though.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 43.3 mpg (US) ... 18.4 km/L ... 5.4 L/100 km ... 52.0 mpg (Imp)


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    Yes, that's the assembly. One part is the intake snorkel and the other is the resonator.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.6 mpg (Imp)


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    Senior Member GrnBn's Avatar
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    Quote Originally Posted by Eggman View Post
    Maybe I'm wrong but I thought the air/fuel mixture was regulated by a feedback loop from the oxygen sensors?
    I was under the impression most cars go to their "open loop" fuel tables whenever you're going WOT, but I could be wrong as I'm not technically trained in any capacity.



    Quote Originally Posted by Eggman View Post
    And if you decide to run without the resonator in place, be sure to replace that little bolt with the 10mm hex head or oil will splash out of that hole.
    I don't think mine goes all the way through the valve cover, but I also didn't leave it open to test that theory. No oil on the bolt itself, ever, though.

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    Administrator Daox's Avatar
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    Typical engines stay in closed loop under WOT a lot. They may drop out around peak torque. Turbocharged engines probably go into open loop a lot easier than naturally aspirated.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing
    Current project: Developing a rear sway bar alternative

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 41.7 mpg (US) ... 17.7 km/L ... 5.6 L/100 km ... 50.0 mpg (Imp)


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    Senior Member GrnBn's Avatar
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    I certainly am not trying to say you'll see any sort of meaningful performance gains from removing the intake snorkel and resonator. IIRC, there aren't any dyno charts saying that the aftermarket intakes offer gains either, so I think we're all chasing a sound at this point. Like I said initially, the car now has a more aggressive intake noise, and for people who desire this they can avoid spending lots of money to make it so. I do think the car breathes more easily, but I'll grant that this doesn't necessarily mean you're getting better performance. If there is any substantive benefit to removing the snorkel and resonator, I would claim it is only at the highest end of the RPM band, say perhaps 4.5k-6k, where the increased air flow makes for marginally better acceleration.


    I've not noticed any reduction of power at low-mid RPMs, or any decrease in my average fuel economy (still ~40s, and it can go higher if I slow down). The biggest difference is how much noise is produced under WOT, with the second most noticeable aspect being the lessening of resistance when engine-braking. I put the pieces back on, just to test everyone's theories regarding the role of the resonator, and the car definitely feels like there is more resistance on the intake air flow. The engine-braking picks back up, but the intake noise is much less. If you want whooshy intake sounds, take these parts off. If you're convinced Mitsubishi put some serious engineering hours into designing the intake pathway, don't mess their design and enjoy your car as it is.



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