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Old 01-06-2012, 08:19 PM   #1
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Default My 3" custom spring loaded flapper valve

JasonC SBB had this thread about removing his spring loaded flapper from a Dynomax VT muffler. It was a great idea and I was going to do the same because my Outback Wagon has a slightly annoying drone. But the ~$90 price tag for the muffler is borderline silly for a slight drone, even though I could probably use the discarded muffler section as a resonator for some future project... So anyway I made one with $15 worth of raw material from McMaster and about $300 worth of my time.

I don't know if it works yet. It probably won't. If it rattles I will make a nice soft stop for the flapper. I will update once I hold it up to my exhaust pipe and make the wife rev it up.

More pictures here:

Flap flap flap

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My 3" custom spring loaded flapper valve-flapper8.jpg  
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Old 01-06-2012, 08:38 PM   #2
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Nice!

Can you mass produce and sell it? Oh wait better check what they've patented. (mm, Patent pending it seems)

Note:

1) that the lever arm must be such that the torque required to hold it open is greatly reduced than that to begin swinging it open. (It almost over-centers). Torque to hold it open is actually almost zero.

2) the Dynomax design has a notch in the small side of the flap for the gas to flow when closed. The notches should not be on the large side so that gas pressure will torque it open

3) the dynomax flapper has some kind of steel wool attached on the edge of the flapper that hits the pipe to prevent clattering noises.
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Old 01-07-2012, 10:38 AM   #3
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Cool, I want to hear a before and after.
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Old 01-07-2012, 12:39 PM   #4
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Quote:
Originally Posted by JasonC SBB View Post
Nice!

Can you mass produce and sell it? Oh wait better check what they've patented. (mm, Patent pending it seems)
Anyone can patent anything these days. If I sold some, I doubt dynomax would go after me. If they did, I'm sure a flapper in an exhaust was done before dynomax's VT. I haven't read their patent, but I'm sure it's the mate of the flapper inside a muffler. This would just be a flap inside a pipe, for intakes. What you do with it is up to you. Errrrrr summin like that. Or I'll sell it without the $1.50 spring.

Quote:
Note:

1) that the lever arm must be such that the torque required to hold it open is greatly reduced than that to begin swinging it open. (It almost over-centers). Torque to hold it open is actually almost zero.
Yar, I figured as much. A side view of where the spring post is with respect to the shaft post would help. The spring post is just tacked there so I can move it around. And there's 4 other springs with different K's in that overall length from McM if I need to change the spring rate.

Quote:
2) the Dynomax design has a notch in the small side of the flap for the gas to flow when closed. The notches should not be on the large side so that gas pressure will torque it open
Interesting. I'll consider that.

Quote:
3) the dynomax flapper has some kind of steel wool attached on the edge of the flapper that hits the pipe to prevent clattering noises.
I saw that. I was going to JBweld some high temp header gasket material to the ID of the pipe as a 'soft' stop but figured i'd try it as is first & do it if it's annoying.

AND thank you for the idea, again.

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Cool, I want to hear a before and after.
Same here. I'll work on that.
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Old 09-15-2015, 12:53 PM   #5
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reviving this.
I need one for my wrx.
asap..........I think

anyone mess with these more or do any more testing?
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Old 09-15-2015, 12:55 PM   #6
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I haven't. I forgot about it actually.
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Old 09-15-2015, 01:16 PM   #7
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like, forgot to even install it?
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Old 09-15-2015, 01:27 PM   #8
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I duct taped it to my exhaust pipe and it was obvious I needed a tighter spring. But at idle, with it slapping around, it was a lot quieter in and out of the car.

It's been sitting on my garage shelf since.
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Old 09-15-2015, 01:41 PM   #9
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urrrrrrrrrrrrrrrrrggggggghhhhhhhhhhhh

I need one real bad.

found one on fleabay. not sure cause it doesn't really state spring pressure or anything. But it's $40, which is good IMO.

Basically I'm trying to figure out a way to tone down the low end pulses on the WRX.
It has a KillerB "holy" header, which flows amazing.
It has a blouch 10cm hotside which flows amazing.
It has a 3", very free flowing exhaust setup which flows amazing.
At WOT and at high rpm, it sounds amazing.

.....but,

At low rpm, I'm talking 1500-2100, I have some serious exhaust pulses/noise that is annoying, that goes away just past 2100rpm.
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Old 09-15-2015, 02:09 PM   #10
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Ahh I See. Is the exhaust tip pointing downwards at all? Does the tip extend out past the edge of the bumper?

Fixing those two issues made me not have to install my flapper mcflapflap.

EDIT: I'm interested in seeing your dyno changes if you weld this into your exhaust though.
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Old 09-15-2015, 02:15 PM   #11
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It's a Cobb quad-tip slant tip exhaust. The tips are only a tiny bit slanted, and no it's not pointing down. Yes they go just a tiny bit past the bumper. It's a really quality piece that actually sounds really quiet on any other setup but mine (my setup right now is, IMHO, perfectly maxed out, 10/10 flowing about as good as it can)


I too am hoping it doesn't hinder the flow too much

What I'm even more interested in is a 2-bolt 3" electronic cutout so I can place it directly into the stream and be able to open it on commant rather than waiting for pressure to do it, but it doesn't seem like that's a thing
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Old 09-15-2015, 02:37 PM   #12
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<p>Somewhat interested in this.. Would be nice to have my car quieter around town, but still the option to be fully open, without having&nbsp;to put in or take out a silencer.&nbsp;<br /><br />Curious, though it will not apply to me, what impact these will have on your turbo spool.<br /><br />In4 guinea pig.</p>
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Old 09-15-2015, 02:46 PM   #13
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see the link to Jasons thread in OP where he did exactly that.
looked real good, minimal effect

no guinea pig on miata, it's already been done.
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Old 09-15-2015, 05:57 PM   #14
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Old 09-15-2015, 06:13 PM   #15
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WUTT!!

that's like, almost everything I could ever want. The question is: how will it hold up? (looks a bit weak)

thanks for that link
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Old 09-15-2015, 06:16 PM   #16
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I never ran it, lol. I know Apexi makes one (not electric), and a buddy ran it on his 300zx and never had any issues.
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Old 09-15-2015, 06:18 PM   #17
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the non-electric part is actually not a problem at all.
I've seen way too many of those electric ones fail after brief use to really trust them.

I'm 99.99% convinced I'm gonna try that one. It requires no cutting/welding, just bolt in and go. hmmmmmmmmmm
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Old 09-15-2015, 06:21 PM   #18
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Let us know how it goes! Here is the apexi one if you're curious, almost identical.

Exhaust Control Valve, Flange-Type (80mm.)
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Old 09-21-2015, 01:06 PM   #19
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My 3&quot; custom spring loaded flapper valve-80-exhaust_ecv_957c0ab8803ae3563397be01aee7fe00d6d9aec3.jpg  
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Old 09-08-2016, 11:11 AM   #20
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Vlad how shitty did that end up being? I've had a strong urge to add a cutout to my exhaust lately.
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