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Discussion Starter #1
OK, here's the 'can't believe this guy doesn't know this' question of the day. While installing the boost gauge on my '03 the rubber hose coming from the wastegate actuator is right behind and under the plastic 'box' that attaches to the air intake pipe. This is the box that shows the '6.6 Turbo' on top of it. I had to remove it to tee into the wastegate actuator hose for my boost gauge.
I was wondering exactly what purpose this box serves? It seems that air may flow into it but the air has nowhere to go except back to the main air pipe that attaches to my AFE Stage 2 intake. Seems like I have heard that some guys have remove this altogether.
What's the scoop? Thanks
 

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Silencer
 

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Take it off, cap the hole and I doubt you'll notice any differance, I didn't.
 

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I think its suspose to act like an resovior. Sorta like the old vacume balls on the old cars but this one has clean pressured air for the engine for those sudden mash gas peddel through firewall times. Now rather or not it makes any difference is another story.
 

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I heard it was a "PLENUM" to improve drivability & smooth throttle response.
 

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Discussion Starter #7
Hmmm... interesting and versatile replies. I'll dig deeper and see what I come up with and let you guys know the results. I'll get in touch with GM and see what they say.
Thanks for the replies.
 

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My understanding is that it is a resonator on the turbo inlet to smooth pressure waves reflected back from the compressor impeller hub. Some thought it was a muffler/silencer - but as you've seen, those that have removed it have noticed no change in engine/turbo noise. I believe it's both cosmetic and does provide some engineered minor benefit to turbo flow, or they wouldn't have wasted the plastic and connections.
 

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These type of plenums are also present on non-turbo engines. My '97 Suburban has one also (or had one before I replaced it with a K & N intake)...and it's a 454 cu. in. gas motor. Hence, I think the plenum theory is in play. It would quiet intake noise and smooth throttle response. But it would be intersting to hear from an automotive engineer who's privvy to the engineering logic behind it. If it was purely cosmetic, I wonder why it would hold intake air as opposed to just being a bolt-on cover.
 

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Discussion Starter #12
I emailed GM via the GM website and received a message back saying, 'We don't know, contact your dealer'. I guess my email went to an office where people just answer phones. Anyway I contacted the dealer prior to this email and received a couple of different answers. One answer was that this was very critical and should never be removed. Another answer was that it helps the turbo breathe. Oh well, I give.
 

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I'm with Idle Chatter. The factory doesn't spend a nickel where it doesn't have to, so there is some benefit. I believe it works as a damper to smooth airflow. I ran with and w/o it, and couldn't really tell a difference. I would like to have checked mileage both ways, but since I use lp it would be too hard to measure any difference.
 

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Anybody That Has A Duramax And Has Power Braked It For One Reason Or Another Has Probably Noticed A Huffing Noise After The Throttle Has Been Released, This Is Caused By Air Being Forced Back Out Of The Intake Because The Turbo Is Still Making Boost But Engine Rpm's Are Not High Enough To Recieve The Boost, This Resonator Allows Positive Airflow Into Itself Further Silencing The Huffing Noise. By Its Position On The Air Intake It Could In No Way Silence Turbo Whine, It Is There To Accept Increased Pressures In The Air Intake Assembly Not Only To Silence The Blow Off Noise But Also To Protect The Air Box, And Filter Assembly. If Negative Airflow Pressures Get To Great, Seperation Of The Air Filter Seals, And Or Connections To The Air Intake Assembly Can Be Comprimised. Not An Important Part For Someone That Can Put A Intake Tube Back Together, But For An Average Person That Never Looks Under Their Hood It Could Be An Unwanted Problem, Due To The Chance Of Contaminants (dust, Water, Particulate Matter, Etc.) Entering The Air Intake Stream.
 

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I have to disagree, Sam. Within the range of compressibility of the intake air charge, the resonator is not going to be a very effective "surge volume" as you predict. That is also not the function of a resonator. I have done some more research and it appears that the box is a Helmholtz Resonator. A helmholtz resonator is basically a gas volume attached to a system to absorb/reflect acoustic pressure waves. The location and sizing of the resonator allows it to produce specifically timed reflective waves to "nullify" unwanted waves. Although acoustic, these are *pressure* waves that travel at the speed of sound. I scanned through some pretty deep theoretical papers dealing not only with automobile intakes, but the intakes of very large axial centrifugal industrial gas compressors (very large versions of the compressor wheel in our turbo). It appears that these compressor wheels produce a series of pressure waves in the intake caused by blade tip passage. These waves radiate out of the intake and back down the intake tube, which is acoustically "solid" which can reduce intake/compression efficiency and also produce some damaging vibration in the compressor wheel (hard on the bearing). A properly tuned Helmholtz resonator chamber will absorb and counter reflect the pressure waves, stopping the vibration and improving the performance. That is the reason for the resonance chamber on our intake. It may not reduce any really audible sound range, but will improve air flow into the compressor and dampen some obviously high frequency vibrations (based upon the size and speed of our turbo). Interestingly enough, I also came across the following advert in my search:

Helmholtz Resonator
Helmholtz resonators are air resonance cavity devices. They can be specified to meet various design goals such as engine torque increases or noise attenuation. The Outlaw Helmholtz resonator is specifically tuned to boost the torque at mid-range RPMs.

That answers the reason and is basis for leaving it alone.
 

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Discussion Starter #16
Now those are the types of answers that I was looking for! I'm leaving mine on. I am wondering if by installing the AFE Stage 2 intake will this then cause the Helmholtz Resonator to be tuned differently than with the stock air filter system thus maybe decreasing or increasing the resonator's effectiveness?
 

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Gene, I think the resonator is either a "compromise" tuning to try and cover a broad range of turbo speeds, or is specific to one "problem" turbo speed/frequency. Due to it's location close to the turbo compressor inlet, I think it's designed to do its thing at or near the turbo. It should be able to perform its function even if the upstream piping and airbox are different. Now, whether the AFE has a tap for the resonator, that's another story.
 

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Snuck in on me, Specialagent!
 

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Discussion Starter #20
I already have the AFE stage 2 and it does have the hole for the resonator. I was just wondering if it made a difference. Thanks for all of the replies!!
 
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