Exhaust Sound Deadening
July-10th-2002, 06:55 AM
#31
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Join Date: Dec 2001
Location: Maine
Posts: 97
My father is going to fabricate an insert for my tailpipe so we can test the exhaust tip.
A year ago we put a dtm stainless muffler on his Acura Vigor and it did the same thing only louder. But if we took the muffler off it was exactly what it should sound like.
So last night we took a plastic bottle and cut the large end off.
If I put the 2" opening of the bottle (top) into the tailpipe, which gives you a 5" opening on the other end of the bottle the sound was better.
If I reversed it, meaning I shoved the bottom of the bottle over the entire tailpipe leaving the 2" opening of the bottle as the exhaust tip it was actually worse. I should have taken some pictures to better explain this.
In conclusion, The exhaust tip could be the culprit. I am still going to try putting a chunk of metal onto the exhaust pipe. I did grab onto the muffler though and the sound did not change.
The saga continues...
A year ago we put a dtm stainless muffler on his Acura Vigor and it did the same thing only louder. But if we took the muffler off it was exactly what it should sound like.
So last night we took a plastic bottle and cut the large end off.
If I put the 2" opening of the bottle (top) into the tailpipe, which gives you a 5" opening on the other end of the bottle the sound was better.
If I reversed it, meaning I shoved the bottom of the bottle over the entire tailpipe leaving the 2" opening of the bottle as the exhaust tip it was actually worse. I should have taken some pictures to better explain this.
In conclusion, The exhaust tip could be the culprit. I am still going to try putting a chunk of metal onto the exhaust pipe. I did grab onto the muffler though and the sound did not change.
The saga continues...
July-10th-2002, 09:10 PM
#32
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Join Date: May 2002
Location: Elizabethtown, Kentucky
Posts: 67
The anticipation grows. The tension builds. My fur would stand on end if I hadn’t singed most of it off during my 4th of July fireworks experiment. 
I investigated the local resources and it looks like I’ll end up using the head off a sledgehammer (4# or 8#? A little more research will tell.) attached to the exhaust pipe with two big-*** adjustable pipe clamps. It’ll have to wait till this weekend before I have the time to try it, but we’ll see.
Keep the all gain without the pain? Watch my exhaust go into catastrophic harmonic resonance and tear itself apart? Knock a new opening in the rear floor panel? Crash and burn my remaining fur off?
Or maybe, just maybe, I’ll lay my ears back and enjoy a sip of that refreshing malt beverage Kentucky is so famous for, content with the non-resonant burble of one sparkling sweet exhaust system…
I investigated the local resources and it looks like I’ll end up using the head off a sledgehammer (4# or 8#? A little more research will tell.) attached to the exhaust pipe with two big-*** adjustable pipe clamps. It’ll have to wait till this weekend before I have the time to try it, but we’ll see.
Keep the all gain without the pain? Watch my exhaust go into catastrophic harmonic resonance and tear itself apart? Knock a new opening in the rear floor panel? Crash and burn my remaining fur off?
Or maybe, just maybe, I’ll lay my ears back and enjoy a sip of that refreshing malt beverage Kentucky is so famous for, content with the non-resonant burble of one sparkling sweet exhaust system…
July-11th-2002, 12:50 AM
#33
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Join Date: Mar 2002
Location: VanCity, B.C.
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man... i can't believe i'm spending work time wondering if it'll work! hahahhaha! hopefully it'll all work out! and if it doesn't you guys can always get more fur from us fur-trading canadians!!! 
I AM CANADIAN!!! 
I AM CANADIAN!!!
July-11th-2002, 09:33 PM
#34
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Location: Elizabethtown, Kentucky
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One other thing I remember about the Nissan exhaust was that people would comment about the tailpipe shaking like crazy when I was running at lower RPMs and they were behind the car. (Also, I'd installed a Remus sports exhaust - it replaced the stock rear section.) I'm thinking that was an indication of a lowered resonant frequency (non-audible) and probably a consequence of the dampening weight.
I calculated the approximate mass of the lead weight I remember on the Nissan and it looks like the 4# sledgehammer is pretty much a perfect match. I picked one up this evening and have a little prep work to do before trying it. I figure the best mount will be to drill out the wooden handle and use the hole for strapping it down. I'll put the MazdaSpeed back on tomorrow night or Saturday morning and then start the trials...
Meanwhile, I'm gonna FedEx Overnight some of that Canadian fur. Just in case. 
I calculated the approximate mass of the lead weight I remember on the Nissan and it looks like the 4# sledgehammer is pretty much a perfect match. I picked one up this evening and have a little prep work to do before trying it. I figure the best mount will be to drill out the wooden handle and use the hole for strapping it down. I'll put the MazdaSpeed back on tomorrow night or Saturday morning and then start the trials...
Meanwhile, I'm gonna FedEx Overnight some of that Canadian fur. Just in case.
Last edited by BigBadWulf; July-11th-2002 at 09:45 PM.
July-12th-2002, 08:20 PM
#35
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Location: Elizabethtown, Kentucky
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The Results:
Took the afternoon off in the name of Science and Research and I’ve got good news and bad news. The good news is the weight does in fact reduce sound levels! Of course this is pretty subjective, but there was a noticeable difference with the “hammerhead” attached. It knocked down (pun intended) the rough edge of sound below 3K RPM by about 10% - smoothed it out, but left a tone with some character. Now the bad news: 3-4K RPM and the cabin still lights-up acoustically, though not quite as bad – probably a 5% reduction in sound levels.
I made test runs with and without the weight attached, and at various speeds up to 80 MPH. Also, I tried 3 mounting locations – as pictured, on the side and on the bottom, all of these at different distances from the muffler. The mounting location didn’t seem to make that much difference, though I think it had a subtle influence on fundamental frequencies.
Bottom line: The MazdaSpeed sound isn’t as “raw” with a weight attached, but it’s still on the loud side. (And I understand how difficult it is to describe the tone of this system – MazdaSchizophrenic might work: Steady throttle, not much noise. Step off the gas, or WOT, and all hell breaks loose.) It depends on your individual threshold of tolerance for the sound levels. It could make enough of a difference that you can live with the exhaust on a daily and extended basis, and then again…
Cheers & have a Great Weekend!
BBW Test Lab
Took the afternoon off in the name of Science and Research and I’ve got good news and bad news. The good news is the weight does in fact reduce sound levels! Of course this is pretty subjective, but there was a noticeable difference with the “hammerhead” attached. It knocked down (pun intended) the rough edge of sound below 3K RPM by about 10% - smoothed it out, but left a tone with some character. Now the bad news: 3-4K RPM and the cabin still lights-up acoustically, though not quite as bad – probably a 5% reduction in sound levels.
I made test runs with and without the weight attached, and at various speeds up to 80 MPH. Also, I tried 3 mounting locations – as pictured, on the side and on the bottom, all of these at different distances from the muffler. The mounting location didn’t seem to make that much difference, though I think it had a subtle influence on fundamental frequencies.
Bottom line: The MazdaSpeed sound isn’t as “raw” with a weight attached, but it’s still on the loud side. (And I understand how difficult it is to describe the tone of this system – MazdaSchizophrenic might work: Steady throttle, not much noise. Step off the gas, or WOT, and all hell breaks loose.) It depends on your individual threshold of tolerance for the sound levels. It could make enough of a difference that you can live with the exhaust on a daily and extended basis, and then again…
Cheers & have a Great Weekend!
BBW Test Lab
July-12th-2002, 09:08 PM
#36
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Join Date: Mar 2002
Location: VanCity, B.C.
Posts: 211
thanks for the post dude!!!
hmm... actually now i'm really curious... cuz if a weight *sorta* worked, then I've got a WHOLE SLEW of ideas popping into my head now... but i'll wait til i get more cash and pick up my own mazdaspeed to experiment... cuz i don't want you guys muck up your systems or waste money due to my hap-hazard physics knowledge! hahahhaha!
hmm... actually now i'm really curious... cuz if a weight *sorta* worked, then I've got a WHOLE SLEW of ideas popping into my head now... but i'll wait til i get more cash and pick up my own mazdaspeed to experiment... cuz i don't want you guys muck up your systems or waste money due to my hap-hazard physics knowledge! hahahhaha!
July-12th-2002, 09:09 PM
#37
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Join Date: Jul 2002
Posts: 18
http://www.umanitoba.ca/faculties/ar...4/resonanc.htm
http://www.umanitoba.ca/faculties/ar...c4/acoust1.htm
http://www.howstuffworks.com/muffler3.htm
Hello guys Im new here. i love read yours posts.
I have the same trouble, my mazdaspeed is verry loud at around 3500rpm maybe the links above may help someone.
I have use a 1/4 inch rubber hose rolled inside the muffler tip to prevent it from vibrating and have little good result. Also i have try it with and with out the second cat and see no result.
Have fun.
http://www.umanitoba.ca/faculties/ar...c4/acoust1.htm
http://www.howstuffworks.com/muffler3.htm
Hello guys Im new here. i love read yours posts.
I have the same trouble, my mazdaspeed is verry loud at around 3500rpm maybe the links above may help someone.
I have use a 1/4 inch rubber hose rolled inside the muffler tip to prevent it from vibrating and have little good result. Also i have try it with and with out the second cat and see no result.
Have fun.
Last edited by marc38; July-13th-2002 at 06:15 PM.
July-12th-2002, 10:08 PM
#38
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Location: Elizabethtown, Kentucky
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Chumpman if I wasn't so tired and had a full tank of gas I'd let you borrow my MazdaSpeed for experimentation tomorrow. That's right, the MazdaSpeed is back in the shed till we come up with a better solution. On a scale of 1=stock and 10=MazdaSpeed in loudness, I prefer a 6 or 7 which is about where my Dynomax falls, it just doesn't look as good.
BTW - I also tried a reducer insert (2 1/2" down to 1 7/8" stuck narrow end first) but somewhere down the road that sucker blew out to god knows where. At least there weren't any cars behind me! Just as well - it really didn't make difference.
marc 38 - thanks for the links!
Rubber hose?! I don't know about your tip, but mine gets so damn hot that I can bake my Hot Pockets in there for supper. Also, that's interesting about the 2nd cat not having any effect on sound levels.
That's right, the MazdaSpeed is back in the shed till we come up with a better solution. On a scale of 1=stock and 10=MazdaSpeed in loudness, I prefer a 6 or 7 which is about where my Dynomax falls, it just doesn't look as good.BTW - I also tried a reducer insert (2 1/2" down to 1 7/8" stuck narrow end first) but somewhere down the road that sucker blew out to god knows where. At least there weren't any cars behind me!
Just as well - it really didn't make difference.marc 38 - thanks for the links!
Rubber hose?! I don't know about your tip, but mine gets so damn hot that I can bake my Hot Pockets in there for supper. Also, that's interesting about the 2nd cat not having any effect on sound levels.
July-13th-2002, 08:32 AM
#39
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Location: Elizabethtown, Kentucky
Posts: 67
I was thinking about exhaust flow and why the DynoMax I’m running has acceptable sound levels. Part of this is probably the design of the muffler – it’s not a straight through. Another issue may be flow. I’m using a Super Turbo model number 17730, which flows 260 CFM. DynoMax published a great formula for determining the exhaust flow requirements for an engine:
2.2 x horsepower = exhaust flow CFM
So a stock engine would give you a flow of 2.2 x 130 HP = 286 CFM
Obviously the system I’ve got is a bit restrictive, but I’m confident it’s flowing better than the stock muffler. A guesstimate of flow for the MazdaSpeed is somewhere between 500 and 1000 CFM – way more than necessary for our horsepower. Another issue of exhaust flow is that its dependent on engine RPM. The higher your revs, the greater the flow.
And we can’t forget about exhaust pipe diameter. (There’s been a healthy discussion about that already.) I’ve not been able to find any good info about the flow ratings of pipe. The engineers I’ve talked to go glazed eyed and start generating pages of data and charts, however, the only thing I’ve gotten from all this is a headache and nothing I can change on my car.
Anyway, I just thought I’d pass along a little more background on the topic.
“Click-Click-ZOOM!”
2.2 x horsepower = exhaust flow CFM
So a stock engine would give you a flow of 2.2 x 130 HP = 286 CFM
Obviously the system I’ve got is a bit restrictive, but I’m confident it’s flowing better than the stock muffler. A guesstimate of flow for the MazdaSpeed is somewhere between 500 and 1000 CFM – way more than necessary for our horsepower. Another issue of exhaust flow is that its dependent on engine RPM. The higher your revs, the greater the flow.
And we can’t forget about exhaust pipe diameter. (There’s been a healthy discussion about that already.) I’ve not been able to find any good info about the flow ratings of pipe. The engineers I’ve talked to go glazed eyed and start generating pages of data and charts, however, the only thing I’ve gotten from all this is a headache and nothing I can change on my car.
Anyway, I just thought I’d pass along a little more background on the topic.
“Click-Click-ZOOM!”
July-15th-2002, 06:59 AM
#40
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Join Date: Dec 2001
Location: Maine
Posts: 97
Well guys I've got some good news and some bad news...
The good news is that I now have the stock silence in the car and louder exhaust outside of the car.
The bad news is that I had to plug the exhaust down to its OEM size to accomplish this.
What I used is a www.staintune.com exhaust silencer. My bike has a stainless exhaust on it and it came with a stainless plug that I took out of it the day I bought it. This plug fit exactly into the muffler (not the tailpipe but in the muffler).
You cannot see it at all! The exhaust is louder and a tad bit raspier (higher pitched (just a smidge)).
Inside the car you can hear the exhaust but it is almost down to stock silence. It doesn't feel like I just plugged it up (horsepower wise), but my butt-o-meter may have been scewed a bit.
Anyway, I know have the mazda speed exhaust without resonance and that is what we are all trying to get at.
I do need to take it out again for some finishing touches, but I'll try and take some pictures soon.
I don't know if Staintune sells the plugs seperately, but my bike is a '97 VFR750.
The good news is that I now have the stock silence in the car and louder exhaust outside of the car.
The bad news is that I had to plug the exhaust down to its OEM size to accomplish this.
What I used is a www.staintune.com exhaust silencer. My bike has a stainless exhaust on it and it came with a stainless plug that I took out of it the day I bought it. This plug fit exactly into the muffler (not the tailpipe but in the muffler).
You cannot see it at all! The exhaust is louder and a tad bit raspier (higher pitched (just a smidge)).
Inside the car you can hear the exhaust but it is almost down to stock silence. It doesn't feel like I just plugged it up (horsepower wise), but my butt-o-meter may have been scewed a bit.
Anyway, I know have the mazda speed exhaust without resonance and that is what we are all trying to get at.
I do need to take it out again for some finishing touches, but I'll try and take some pictures soon.
I don't know if Staintune sells the plugs seperately, but my bike is a '97 VFR750.
July-15th-2002, 12:19 PM
#41
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Location: Elizabethtown, Kentucky
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Sweet! That sounds exactly like what we're looking for - good for those extended trips and occasional "quiet" time with the option to be as loud as we want to be. Look forward to the pictures!
July-15th-2002, 03:51 PM
#43
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Join Date: Oct 2001
Posts: 484
Originally posted by Sweedenhouse
Will any of this **** work on the Bosal catback as well? I hate my friggin exhaust.
Will any of this **** work on the Bosal catback as well? I hate my friggin exhaust.
July-16th-2002, 06:14 PM
#45
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Sweedenhouse –
douggie already mentioned what I was going to offer - I remember hearing that Bosal has a silencer tip for their exhaust. Also, you might try Mitch at protege5online.com; he’s a pretty good resource. That’s the problem we’ve been up against with the MazdaSpeed - there isn’t a silencer tip available.
marc38 –
Awesome! There was a formula I was using a few posts back for the frequency we’re dealing with and your results confirm the numbers! 115 HZ = 3,450 RPM engine speed (Cycles Per Second of reading x 60 seconds / 2 exhaust pulses per crankshaft revolution = engine RPM) So if your 115 HZ reading were +/- 10 HZ, we’d have a range of 3,150 to 3,750 RPM.
Now what I wonder if this is a resonant frequency related to the length of the P5 exhaust? Knowing sedans have a longer exhaust system, do the ones with the MazdaSpeed axle-back have the same problem around 3,400 RPM? Anyone?
douggie already mentioned what I was going to offer - I remember hearing that Bosal has a silencer tip for their exhaust. Also, you might try Mitch at protege5online.com; he’s a pretty good resource. That’s the problem we’ve been up against with the MazdaSpeed - there isn’t a silencer tip available.
marc38 –
Awesome!
There was a formula I was using a few posts back for the frequency we’re dealing with and your results confirm the numbers! 115 HZ = 3,450 RPM engine speed (Cycles Per Second of reading x 60 seconds / 2 exhaust pulses per crankshaft revolution = engine RPM) So if your 115 HZ reading were +/- 10 HZ, we’d have a range of 3,150 to 3,750 RPM. Now what I wonder if this is a resonant frequency related to the length of the P5 exhaust? Knowing sedans have a longer exhaust system, do the ones with the MazdaSpeed axle-back have the same problem around 3,400 RPM? Anyone?