What is the quietest 3" straight through muffler I can get?
#23
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!)
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!)
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...
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.
#29
"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".
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".
#30
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.
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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