..okay,i've built a few custom exhausts so far,and a couple have had problems that i can't seem to get rid of.

both exhausts i've built for my hatchback have had a problem with a rattle at certain RPMs.
the first was a 2.25" setup for the old D16.it consisted of an 18" long resonator back to a Dynomax turbo muffler.it was one piece with no flanges,and connected to the header with a stock style flange.
the second is 2.5" for the B20.it consists of a stock flange at the header connection with a 2" to 2.5" flare,a 12" Dynomax resonator test pipe,20" Dynomax resonator in the stock location,V-band flange at the stock axle-back location.at first i had a Magnaflow oval muffler,but it was too loud.i then switched to a twin-loop style muffler.

with the old exhaust,at about 1500 RPMs as you accelerated(at any throttle position)there was a rattle kind of sound for about a 100RPM interval.
with the new setup,the same thing happens at both 1400RPMs and again around 2000RPMS(with both mufflers i've had on there).
i'm using factory rubber hangers at all the factory locations,and none of the piping is anywhere close to hitting anything.i've also since added engine mount inserts,to eliminate the possibility of engine movement contributing to it.all welds are nice and solid,no leaks,and braces have been added where needed.all three of the setups sound very good,other than this problem.

i can't figure out my problem.i thought maybe the resonator or muffler on my old setup was falling apart internally,and that prompted me to build the new exhaust.i'm experienceing the same problem,but at different RPMs.it happens only at these points,and at ANY other RPM the sound is perfect.
is there a chance that the combination of piping length and diameter has some kind of resonance that i could possibly "tune" out?or,am i reading way too much into it?i've noticed some newer vehicles have a rubber mounted attachment on the exhaust that looks to me to be nothing other than a damper.is it possible that this is a fix for the same kind of problem?if anybody here has ever ridden in a 94+ Integra with a stock exhaust,you may have noticed that their OEM exhausts are practically silent,but they all seem to have a loud resonance/rattle at a certain RPM.i'm thinking this is the same kind of problem?

do ya'll think that running stiffer rubber hangers would allow the exhaust to move less and maybe suppress the rattle?or,would softer hangers maybe "absorb" the vibration?

i'm at a loss here on how to fix this,and it makes me mad that something so simple and stupid is such a big problem for me.this is my daily driver,and i have to listen to the stupid noise every time i take off from a light-i feel like i look and sound as dumb as the riceboy who has a fartcan sounding like a weedeater

any insight appreciated.
THANKS
Chris


Modified by TeamNextGenChris at 10:14 PM 10/2/2005

 

In my own experience an exhaust is the simplest yet hardest thing to get to work right on a car. If it doesn't leak from somewhere, it rattles. If it doesn't rattle, it makes unpleasant sounds at certain rpms.

From what you describe, your problem could be caused by the lack of a flexible joint at the axle-back. The use of Dynomax resonators which use fiberglass as sound absorbtion material (IIRC) must also not be helping.

Also, anything short of a stock muffler will sound ricey on a Honda. It's just a sad truth we have to deal with. If your looking to build a fart free free-flowing exhaust then that's your problem right there ; there is no such thing.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jamez &raquo;</TD></TR><TR><TD CLASS="quote">In my own experience an exhaust is the simplest yet hardest thing to get to work right on a car. If it doesn't leak from somewhere, it rattles. If it doesn't rattle, it makes unpleasant sounds at certain rpms.

From what you describe, your problem could be caused by the lack of a flexible joint at the axle-back. The use of Dynomax resonators which use fiberglass as sound absorbtion material (IIRC) must also not be helping.

Also, anything short of a stock muffler will sound ricey on a Honda. It's just a sad truth we have to deal with. If your looking to build a fart free free-flowing exhaust then that's your problem right there ; there is no such thing.</TD></TR></TABLE>
i haven't even thought about the axle joint.but,on the other hand,plenty of aftermarket exhaust replace that joint with a solid 2 or 3 bolt flange.
i'd also considered the resonator,although i don't think it's the cause of the noise,unless maybe the perforated core is loose and rattling.i'd considered using a higher quality resonator to maybe quiet it down even more(the overall volume,not the rattle).
i agree about the exhaust tone of a Honda-that's why i'm trying to build a super quiet straight thru exhaust.what i have now i'd say is comparable to the new 350Z's stock exhaust tone-it's almost like stock Honda in sound level,with a tone that's very clean and not bassy or raspy.

so,do you have any input on an exhaust having a resonant frequency that's at an audible frequency?

chris

 

The problem with glass packed resonators is they burn out very quick. Then there isn't anything left to absorb resonances and you get that annoying raspy note.

On my personal exhaust I first tried an ITR axle-back mated to a GSR mid-pipe. I had removed the resonator all together in a misguided weight saving attempt thinking with a stock muffler it couldn't be so loud. It sounded horrible so I had to put one back in. The only thing I could find at the time was a Cherry Bomb. At first it sounded all right but it soon burned out. Still not so bad because I had a stock cat in there but once I put a higher-flowing Magnaflow unit then it went all out raspy again at the engine speeds you mentionned.

So the moral of my story is you need a good quality resonator that won't burn out on you AND a cat or suitable replacement resonator. Not only one or the other.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jamez &raquo;</TD></TR><TR><TD CLASS="quote">The problem with glass packed resonators is they burn out very quick. Then there isn't anything left to absorb resonances and you get that annoying raspy note.

On my personal exhaust I first tried an ITR axle-back mated to a GSR mid-pipe. I had removed the resonator all together in a misguided weight saving attempt thinking with a stock muffler it couldn't be so loud. It sounded horrible so I had to put one back in. The only thing I could find at the time was a Cherry Bomb. At first it sounded all right but it soon burned out. Still not so bad because I had a stock cat in there but once I put a higher-flowing Magnaflow unit then it went all out raspy again at the engine speeds you mentionned.

So the moral of my story is you need a good quality resonator that won't burn out on you AND a cat or suitable replacement resonator. Not only one or the other.</TD></TR></TABLE>
i appreciate the advice on the resonator-i think my current one is going south as the exhaust has gotten slightly louder.what brand(s) have you tried and had good luck with?i also currently have a Dynomax resonator in place of the cat.
also,the problem i'm having isn't a raspiness,it's actually a rattle/vibration.
Chris

 

you dont happen to have the stock header do you? I know there have been problems with some of honda's stock headers coming unwelded inside and rattling around.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 2old_honda &raquo;</TD></TR><TR><TD CLASS="quote">you dont happen to have the stock header do you? I know there have been problems with some of honda's stock headers coming unwelded inside and rattling around.</TD></TR></TABLE>
it did it with the D16 with both a header and stock manifold,and with the B20 with a stock manifold and two different headers...so,that rules that out
Chris

 

I have the same kind of thing going on. At first I thought it could be heard from outside the car also. I had someone drive my car and I couldn't hear it when they drove past me standing on the street. I think alot of the reason I am noticing it is that I can't hear my exhaust inside the car at low rpm's so it makes all the other little noises stand out. I think with the flexibility of the stock system you don't get the noise, and usually when you upgrade you get a louder exhaust note and it masks the noise. For ref my setup is 3" w/vbands from turbo back, 3" cat, and a 2.75" RSR oval.

 

Do you have a flex section? Was there ever one on there before? If there is no flex section the motor may be moving a little more in that RPM range and making the exhaust rattle against something.

The exhausts I have built have been for DSM's which came with a flex section from the factory after the downpipe before the cat. We always put a new flex section in and had no problems with any rattling.

I have a 95 dc2 but I havent even looked at the exhaust yet.

 

it has the factory spring loaded ball type flange in the stock location.
there's no way it's rattling against anything-it's not even close.
Chris

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TeamNextGenChris &raquo;</TD></TR><TR><TD CLASS="quote">
also,the problem i'm having isn't a raspiness,it's actually a rattle/vibration.
Chris</TD></TR></TABLE>

Is it a kind of high pitched metallic clashing sound?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jamez &raquo;</TD></TR><TR><TD CLASS="quote">

Is it a kind of high pitched metallic clashing sound?</TD></TR></TABLE>
kind of.it's not like the "brap" you get with a header.it sounds like a high frequency rattle-like two pieces of metal vibrating against each other at a fast rate.
Chris

 

yeah, I know what you mean then. That's like the next stage of raspiness and you often hear it on cars without a cat and/or resonator. I just checked up on Dynomax's site to confirm they are glass packed and also saw that the "Bullet Muffler" is advertised as "Moderate sound control — RACE USE ONLY!"

If that's what you are using instead of a cat I would look no further and get a real cat converter in there. Then if it's still raspy I would look into a Magnaflow resonator/round muffler, they have stainless steel mesh as a packing material and then whatever the hell "high temperature accoustical suppression material" means.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jamez &raquo;</TD></TR><TR><TD CLASS="quote">yeah, I know what you mean then. That's like the next stage of raspiness and you often hear it on cars without a cat and/or resonator. I just checked up on Dynomax's site to confirm they are glass packed and also saw that the "Bullet Muffler" is advertised as "Moderate sound control — RACE USE ONLY!"

If that's what you are using instead of a cat I would look no further and get a real cat converter in there. Then if it's still raspy I would look into a Magnaflow resonator/round muffler, they have stainless steel mesh as a packing material and then whatever the hell "high temperature acoustical suppression material" means.</TD></TR></TABLE>
i have one of the Bullet mufflers as my test pipe and as the resonator.on a few occasions i've used added them to exhausts that were too loud,and they make a noticeable difference.they seem to last pretty well before blowing out too.
i think i'm going to replace the main resonator with a Magnaflow unit,just to try to quiet it down a little more.BTW-that "high temperature acoustical suppression material" that Magnaflow uses is just fiberglass packing.the perforated core is wrapped in stainless mesh,then the body of the muffler is filled with fiberglass.BUT,it does look to be better built than your average Cherry Bomb type glasspack.
i did some testing today,and i think i found the culprit.amongst other things that didn't eliminate the rattle,i removed the strap that mounts to the engine above the oil pan,and to the header collector.that seems to have cured it!it had no pressure on it-meaning it wasn't pulling up or pushing down on the header.also,it wasn't even remotely close to anything it could rattle against.all the bolts were tight too.i don't know-weird.
i DO know that i don't want to leave that brace off,as it relieves a lot of the stress off the header mounting bolts.when i install the new resonator,i think i'm also going to chop off the stock size collector on my header and go to a 2.5" collector.at that time i'll also add some kind for attachment for that brace.

THANKS for everybody's help!
Chris


Modified by TeamNextGenChris at 8:24 PM 10/4/2005

 

Did you look at your heat shields? I know one on my car developed a small crack..... its started to rattle at certain rpms. It was the one under the car by the gas tank.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TrueNorthStar &raquo;</TD></TR><TR><TD CLASS="quote">Did you look at your heat shields? I know one on my car developed a small crack..... its started to rattle at certain rpms. It was the one under the car by the gas tank.</TD></TR></TABLE>
don't have any anymore
thanks for the suggestion though.
Chris

 

anything hitting? i know when i got mine exhaust welded up i didnt have a flex pipe in there and it broke a bracket for the header. then at certain rpm's it'd rattle like mad.