What is the quietest 3" straight through muffler I can get? - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-17-2008, 05:14 PM   #21
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So the dynomax race muffler for the resonator. correct???

Do you think the 23 1/2 in will fit. Or do I need to get the 16 1/2 in.

Thanks.
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Old 09-17-2008, 05:52 PM   #22
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Mine is bigger than all of you Peewees. 5x8x22" x 2.5" dia. 39 y.o. with very good hearing (audiophile type), but I do have a 200 cell Maremont metal cat. It's quieter than any aftermarket system I've heard yet.

Jason, where did you buy your muffler?

Thanks
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Old 09-17-2008, 06:44 PM   #23
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I'm intrigued. Can you explain this 12" rule? Where you got it from?


Quiet as my car is, I considered this system:

http://autospeed.com/cms/article.html?&A=0883

A butterfly valve after the muffler, that is very partially closed in vacuum, and opens under boost. The partially closed valve will only add 1-2psi of backpressure during cruise, and significantly reduces noise (IIRC > 8 dB in their testing!)
Those numbers are out of a book called "The Scientific Design of Exhaust and Intake Systems". That book was published in the 60's I think. Had lots of good info in it.

For example, glasspacks reduce the intensity of the sound. Say X=length and I=intensity of the sound. (Note Intensity and dB's are related, but not linearly). The rate at which it reduces sound is something like I*X^1.6. That is, as the glasspacks length gets longer, its affects become more and more evident.

So with that in mind, I did this...
Name:  Exhaust12.jpg
Views: 59
Size:  95.2 KB

That's 75" of actual glasspack. Two 24" core ones and a 27" core one. I cut the extra 3" off each end so that it's more like one large one instead of 3 small ones. That way if a sound wave is say 5' long, my system catches the entire thing, where if the sound wave is 3', I'll catch it twice. But when you have gaps between them, then part of the wave always escapes.

The 12" rule is just the number they came up with through testing. You want 12" of straight pipe before it exits. No bends. More length is better, but 12" was the point of diminishing returns.
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Old 09-17-2008, 06:50 PM   #24
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that exhaust must weigh a ****-ton
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Old 09-17-2008, 07:00 PM   #25
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that exhaust must weigh a ****-ton
lol. Yeah it's about as heavy as the old exhaust system was. I don't care though, it sounds good. DEEEEEEP, if you can imagine. Plus I'm still NA, so for 3" NA it isn't bad. It will be even quieter when I get the turbo on.
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Old 09-17-2008, 07:25 PM   #26
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Originally Posted by JasonC SBB View Post
Mine is bigger than all of you Peewees. 5x8x22" x 2.5" dia. 39 y.o. with very good hearing (audiophile type), but I do have a 200 cell Maremont metal cat. It's quieter than any aftermarket system I've heard yet.
mine's the 5x11x22... who you callin peewee, peewee?

PS You can get all these at Summit Racing.

Todd: I used the 12" bullet.
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Old 09-17-2008, 08:24 PM   #27
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Hmm. Do you think the 18" would be any noticable differance on power. Or not enough to worry about. I doubt it would even drop any. What do you think.

I may order a resonator tonight.
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Old 09-17-2008, 09:18 PM   #28
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18inch what? bullet? i doubt there's a 2% difference between resonator and no resonator.... less from 12 to 18
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Old 09-18-2008, 01:34 AM   #29
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"The Scientific Design of Exhaust and Intake Systems"

I know OF that book; I saw it at a local used book shop for some big bux.

So 12" of straight pipe AFTER the muffler helps make it quieter?

Did it say anything about resonated tips?

Hey peewee, mine's quieter than yours because girth is 2.5" and yours is 3".
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Old 09-18-2008, 01:42 AM   #30
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Yeah, MSU library here has that book. I was gonna buy a copy and it's like 100 bucks used. So I think I checked it out like 6 times last year instead. Yes, 12" helps. They had a reason for it, but I don't remember it. Book said tips are a 100% waste. They do nothing but add resistance and turbulence.

But I would like to get a copy of it one day. Has Sooooo much information in it. It's all you would need to design intake manifold and headers. I was designing a set of headers for a V8 guy on m.net and used that book to determine the specs.
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