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Thread: Capped Helmholtz chamber (Drone Eliminator)

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    Addicted Member BigRed585Lbs's Avatar
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    Exclamation Capped Helmholtz chamber (Drone Eliminator)

    Mod time. Capped Helmholtz chamber app. 29'' long. Die, drone, die!





    http://www.g8board.com/forums/showthread.php?t=16077
    Last edited by BigRed585Lbs; 05-05-2010 at 03:41 PM.

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    VIP Member avintegrator's Avatar
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    BigRed, I've been reading the thread over at the other place and i'm thinking about doing the same thing. I have the same exhaust and while i love the sound there are times that i think why the hell does it have to get so loud. Normally i end up in the highway in 5th because the drone is annoying when my wife is in the car. Now all i have to do is find a good place here in town that won't charge me an arm and a leg to do this. Maybe your mod and some dynamat?

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    Addicted Member BigRed585Lbs's Avatar
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    This mod deals with the 8-cylinder drone, knocking it out completely, and decreasing the 4-cylinder drone when the AFM/DOD kicks in, to an acceptable level. No lie, 80-year old's sitting in the backseat do not find it objectionable. That tells me it works.

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    Beyond Help Slizzo's Avatar
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    So this completely eliminated drone? And you said it's capped off on that end just hanging out there turned back towards the front of the car?


    Hmmm.... Maybe I should have my local exhaust shop do this for me...
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    Addicted Member BigRed585Lbs's Avatar
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    There are two drone freqs to deal with on a G8 GT with AFM/DOD operational.

    For example if, in 8-cylinder operation the drone freq was 115 Hz, in 4-cylinder operation it would be HALF that, or about 57 Hz. Helmholtz chamber length would need to be 28.7" to cancel out the 115 Hz freq (that's what I used). To deal with the 57 Hz drone, the chamber would have to be 58.93" long, or TWICE as long as the 115 Hz chamber length.

    The capped off end is tack-welded to the main pipe of the axleback to prevent more vibration, or sound.

    The theory behind this is explained on the other forum.
    Last edited by BigRed585Lbs; 09-21-2009 at 04:50 AM.

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    VIP Member GXPaycheck's Avatar
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    What do you use as a muffler with this setup?
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    Addicted Member BigRed585Lbs's Avatar
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    Looks like the original thread has been "modified" by the Administration into this so they must want to filter out the B/S and get down to the real nitty-gritty!!

    Parts used: Dynomax #42426 stainless steel j-bend 2" diameter, available from Jeg's or Summit, your choice. Cost about $22 ea. 2 required. Cut/fish-mouth the long leg to match the main pipe of the axleback. You also need two 2" diameter stainless steel fender washers (got mine at Lowe's) to cap off the end of the short leg of the j-pipe AFTER you weld up the hole in the center of the washer.

    Cut a hole to size in the axleback and weld the capped j-pipe on to this hole. Tack the j-pipe whereever it touches the axleback to prevent vibration.

    With a file or die grinder, clean up any protrusions to the inside of the axleback tube you may find, as well as the flange if the mating face of the flange is not flush. Makes tip adjustment easier. Any questions? There'll be a pop-test at the end of this class.
    Last edited by BigRed585Lbs; 09-21-2009 at 08:15 AM.

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    Addicted Member BigRed585Lbs's Avatar
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    How many mufflers do you need? Pontiac saw fit to supply us with FIVE. We're getting rid of two of them to make this car sound like it has a V-8 in it.

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    Addicted Member BigRed585Lbs's Avatar
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    More pix:



    Hope this stimulates y'all. On the other forum, you'll see where others have applied this to axlebacks with mufflers, too, although this was primarily aimed at PM-FL and SLP Loudmouth axleback drone problems. There's some inovative pipe welding going on now in the community, although not very much inovation in the exhaust manufacturing industry.

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    Looks ugly as sin but since it works I'm not going to complain. I'll keep my quite G8 right now.
    Don't be jealous because my G8 is Orange...

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