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Old 06-13-2019, 03:03 PM   #1
Andresinibus
 
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Muffler part name? Function?

I went under my car today and right by the differential I found this two weird pieces on each muffler look like valves but nothing attached to them I tryied uploading a pic I hope it shows can some one tell me what they're and what they're for thanks
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Old 06-13-2019, 03:08 PM   #2
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I believe those are the variable exhaust baffles. They mechanically open and close based on back pressure from your engine exhaust (i.e., when your cruising comfortably they tend to make your mufflers quiet but when you go WOT they open up to increase exhaust airflow and sound).
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Old 06-13-2019, 05:19 PM   #3
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they may do that too, but their primary purpose is to smooth out the pulses when in V4 mode.

Without them, V4 mode exhaust pulses are more noticeable and some people get butt hurt over that sound when cruising so they added those valves to make it more uniform with the sound of the v6 cruising.

These are the mechanical versions of the active electronic ones the V8 has for AFM valves.
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Old 06-14-2019, 03:34 PM   #4
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I wired mine open with safety wire and put hose clamps on them to prevent any rattles (they were floppy lose side to side).
I did not really notice any significant difference in sound but did notice a small improvement in mid-rpm response.
I would attribute the improvement to reduced back pressure of course.

But again it was a small change.
Don't expect it to run like a V8 or anything if you wish to try doing that.

Dirt cheap "mod" though, and totally reversible if you change your mind.
People spend lots of money for back pressure reductions.
This is nearly free to try.

The AFM valves on the other hand apparently bypass sections of the mufflers for sound control (or at least that is my understanding of them).
There are videos where someone from Chevrolet talks about them being to achieve that "Camaro" sound for example.

The passive spring loaded plates are ahead of the mufflers so they add back pressure all the time.
Having passive restrictions in the exhaust system offends my engineering sensibilities.
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Old 06-14-2019, 04:20 PM   #5
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the bypass muffler valves you speak of are the npp valves and are not standard on all v6's.

those are by the tailpipes after the muffler. They're electronically controlled. These have nothing to do with afm, just a street legal electric muffler cutout that somehow skirts laws against muffler cutouts.

The valves that are closer to the rear diff are afm valves and they're mechanical on all v6s'. They dont do anything but respond to pressure waves to adjust the sound of the exhaust pulses. They are by their nature an obstruction ...but it's not going to impact performance really, just sound (it's installed and operating on the car when they do all their 0-60 and quarter mile tests that are better than what most people can manage in real life so ...)

Pretty much any aftermarket exhaust solution will have you cutting the afm valves off. They pretty much all also have you losing the npp valves too, but that's a different issue.
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Old 06-14-2019, 06:24 PM   #6
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Sounds like the AFM valves if you have an auto.
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Old 06-14-2019, 11:30 PM   #7
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Quote:
Originally Posted by cellsafemode View Post
The valves that are closer to the rear diff are afm valves and they're mechanical on all v6s'. They dont do anything but respond to pressure waves to adjust the sound of the exhaust pulses. They are by their nature an obstruction ...but it's not going to impact performance really, just sound (it's installed and operating on the car when they do all their 0-60 and quarter mile tests that are better than what most people can manage in real life so ...)
I do agree with your basic premise that they were present when specification testing was performed, and therefore if they are not hurting anything why defeat them?
In my case however I discovered the passive flap valves while chasing some annoying buzzing/resonance noises in the exhaust.
I had my wife rev the engine while watching them and saw (and heard) how they operated.
Once they were wired open and hose clamped, the annoying resonance noises disappeared.
Sadly, exhaust "flap" noises are not at all limited to the motorized versions.

BTW, my speed racer days wound down when I sold my 911 some years ago.
I don't really care about 0-60 and quarter mile numbers for my car, and it will never see a race track for as long as I own it.
But I do still care about handling, efficiency, responsiveness and NVH ride comfort.

It's just my thing......
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