FAQ: The Exhaust Thread

albertj wrote:

I decided to "silence" my exhaust, a friend will help me pull this off on New Years' Eve. "Film at eleven."

Albertj

So here is the "film."

Installed a GM exhaust, the GM RPO for the '04 Park Avenue Ultra. p/n 25749911. One welded assembly with a cat, resonator, 2 mufflers, all pipes, in T409 stainless (exc the polished tips, I can not tell if they are chrome plated or T304 - probably plated 409's my guess. It is 12 feet long.

It fits pretty much right off the truck, just needed to modify the heat shield for the rear oxygen sensor wiring 'cause the bung is fore of the old OE location by a couple inches. If you get one of these you can put on a new bung and plug the old, or extend the wire cover (easily done with sheet metal and pop rivets). And you should extend the front heat shield over the cat (they moved it forward I suppose to make it light off better) with sheet metal; I epoxied the new extension to the OE heat shield. For $50 you might get the PAU heat shield and install it with the muffler, though.

The 25749911 hangs from the exact stock Riv locations (thanks Jason) and came with new rubber hangers. The rear muffler cans are somewhat bigger than the OE Riv cans but still fit the stock locations, and the tailpipes come out to chrome round anglecut and rolled tips just under the outer corners of the bottom of the rear bumper cover. Unlike the OE Riv tips, these stick out a little from under the lip of the bumper cover.

I kind of miss the custom exhaust's growl and rumble already - but not that much. It went to a great home on a buddy's '96 Riv, which is way better than just hanging it in the man-cave. However, on the shakedown drive I noticed the flat spot in acceleration I had with the OE mufflers did not come back (yay!). And it's running great. I suppose that due to age and use the old cat may have been partly blocked, but I really don't know - when I looked at it/thru it I could see thru to the other side okay - but in the "honeycomb" substrate it could be the case that it had blocked over time toward the outer edges of the oval cross-section, and I did not open the can to check if I could see through along the edges. It's not uncommon to have peripheral blockage in a cat over time, I am told, because the cats run hotter in the center than at the edges, and they may soot up over time in the cooler regions. In the center due to extreme heat the soot would always burn off unless you misfuel or some such and poison the catalyst.

So I am thinking that (a) the flat spot maybe was my imagination (b) replacing the plugs and ignition module (for maintenance) maybe actually did the trick - plugs had been in a bit more than 100K miles and were worn (c) the new exhaust is different; the muffler cans are bigger than the Riv's were (d) something else is going on.

And it is really, really quiet. I guess in part because of the sound deadening I did for the custom muffler and in part because this exhaust seems quieter than the OE Riv's due to those bigger muffler cans. Now the loudest sound in the car when rolling is the tires (my snows whine). After it's on a while I'll get the sound meter and measure dB at idle and cruise. The custom pipes registered 80-some dB at cruise before and I think 69dB at cruise after adding eDead and a mass loaded vinyl barrier in the trunk and under rear seat. My post earlier this thread says what the measurements were. As for new measurements We Shall See. I'll take the sound meter out on a cruise soon.

Albertj

Wow, very cool. How about a vid of the sound albert?

Rickw wrote:

albertj wrote:

However, on the shakedown drive I noticed the flat spot in acceleration I had with the OE mufflers did not come back (yay!), I guess in part because of the sound deadening I did for the custom muffler and in part because this exhaust seems quieter than the OE Riv's due to those bigger muffler cans.
Albertj

How could a flat spot in acceleration be eliminated by sound deadening?
I can understand the performance of the engine being affected by the exhaust system itself but not by sound deadening materials that were added to the chassis.

I assume that was a big typo on my part.

This week I am working on a business plan, and one thing I noticed that was happening today is that my palm and/or thumbs brush the touch pad on the keyboard (I have a *small* laptop) and sometimes ends up cutting text. I noticed it earlier today as I was writing. I usually spot it to fix it but sometimes not, and I have turned the trackpad off for the time being. I open up a RivPerformance window and will write a little of a post at a time during short breaks in working, and I suspect what you saw basically was a typo or I just did not complete the thought before I hit 'send.' .

As for your point - that's a great point and true of course. Flat spot is not affected by sound deadening. I think the problem in the post is that I wanted to mention that the loudest sound in the cabin at cruise now is the whine from the tires, I guess in part due to the sound deadening and in part due to whatever's in the bugger muffler cans.

So - I'll go back and fix the post...

With the old exhaust, I had a 'flat spot' in acceleration. Sound deadening had nothing to do with gettiing rid of it -- the new SS exhaust seemed to. Back to the point -- I was expecting the flat spot to come back with the new OE exhaust, and it did not. And it's running great.

I suppose that due to age and use the old cat may have been partly blocked, but I really don't know - when I looked at it/thru it I could see thru to the other side okay - but in the "honeycomb" substrate it could be the case that it had blocked over time toward the outer edges of the oval cross-section, and I did not open the can to check if I could see through along the edges. It's not uncommon to have peripheral blockage in a cat over time, I am told, because the cats run hotter in the center than at the edges, and they may soot up over time in the cooler regions. In the center due to extreme heat the soot would always burn off unless you misfuel or some such and poison the catalyst.

So I am thinking that (a) the flat spot maybe was my imagination (b) replacing the plugs and ignition module (for maintenance) maybe actually did the trick - plugs had been in a bit more than 100K miles and were worn (c) the new exhaust is different; the muffler cans are bigger than the Riv's were (d) something else is going on. The something else: to the OEs, Arvin (and the mufflers on the new exhaust are Arvins) has supplied this 'dual mode' technology since 2002 they say:

http://www.arvinmeritor.com/products/car/pdfs/toyota_dual_%20mode_muffler_ext.pdf

I do not know which GM mufflers use this technology. On the one hand they do not have the out-of-the-shell loop as pictured. On the other hand the cans seem bigger than the OE Riv ones, and one could easily get that loop inside a bigger can -- and I can't see how it would cost any more to make. On the third hand, GM is not known for spending 'extra' money, so the cans likely ahve conventional guts. It will be some months before I can find out. I'm not cutting a can open...

Anyway - for what it's worth the marks stamped on the mufflers are:

GM
G7-5179-R
ARVIN B
AM 2818

and

GM
G7-5179-L
ARVIN C
AM 0639

Resonator is

GM
C6 5961
AW
1 183 9

Hope this helps

Albertj

deekster_caddy wrote:

Wow, very cool. How about a vid of the sound albert?

Not sure it's worth it. They are quieter than the 'burbling' OE ones.

If they really flow as well as they seem to, would make a great 'sleeper' exhaust.

Albertj

Has anyone out there ever removed the resonator and left the factory mufflers or remove the mufflers and replace them with straight pipes w/nice tips??Wondering how this would sound without having to try it myself before I do my full custom exhaust because no exhaust companies see the value in offering us some systems.

my guess is the resonator is a 'helmholtz' type silencer (after all it is made by Arvin on the OE system) intended to push the sound of the exhaust below the audible range (basically converting it to heat via resonance)

reason for this guess is I did some more sound measurements.

First a reminder:

A-weighted measurements means, roughly speaking, measuring the sound pressure levels primarily (in the middle to high octaves) from 500 to 8000 hz. People can hear from around 20 Hz to 20,000 Hz but a s a practical matter due to physiology and environmental damage (loud music, occupational noise, or what have you) most people don't hear all that well outside of the 500 to 8000 hz range.
So you could say that A-weighting discounts the lower and higher frequencies that the average person cannot hear well. One use of this weighting is to reckon the audio performance of telecommunications (2way radios, phones, and such) equipment.

C-weighting measures the bottom (~16 Hz) and top (~16,000) octaves discounted 10dB and does not discount sound pressure levels in the octaves between. C-weighting gives you a better reckoning of sound levels in musical performance (of stereos, music halls, and the like).

With the PAU exhaust I got;

PARKED, ENGINE OFF

55-60 dB-A (decibels, A-weighted)
55-70 dB-C (decibels, C-weighted)
I figured a baseline would not hurt. The question kind of is, how much and how intense is the background noise verusus the noise generated by engine/drivetrain/tires/wind rush. I did not measure octave by octave to find out where (what frequency) that noise was. I was parked in a rural area off a 2-lane secondary road. 55 dB would be the plain old background (there is an interstate about a mile away, that and wind thru nearby trees account for the 55 dB), and 60 or 70 dB is where the meter peaked due to passing cars nearby)

START/COLD IDLE

63 dBA
74 dBC
The point is that the engine and drivetrain, in my Riv, make noise at idle that are, in the cabin, louder than ambient where I live. I was in a rural area. It would not surprise me to find that in some urban environments or near a busy street/highway, one could not hear the Riv idling because ambient noise drowns out the idling motor's sound.

HIGHWAY CRUISING

63-66 dBA
78-83 dBC

What I really measured here was cruising at 65 on asphalt, on concrete and accelerating to 70 taking A and C-weighted measurements, then just putting the ranges down. The way this was done is there is a patch of highway near me that crosses several bridges, were all built and opened about the same time (a city bypass interstate link). So in the space of a couple miles I could see the measurements, slow back down, push the weighting button to change from A to C on the meter, then measure again - exit at a flyover and run back the other direction on similar surfaces to verify.

What I noticed was that the C-weighted sound pressure level (SPL) was substantially higher than the A-weighted - leading me to believe that the Riv is engineered to resonate such that a lot of what you would hear as noise gets pushed out of the typical audible range.

Why?

The hint to me here is: the Riv has a HUGE resonator. I suspect that they are using the huge resonator to lower the frequency of the engine noise, then due to the rigidity of the cabin, the cabin does not resonate such that the noise comes back as a harmonic. Think of the resonator as a really long, relatively fat organ pipe. Unmuffled, the 3800 rasps like a cicada on steroids. That resonator shifts the rasp and in addition, the funky-shaped Y-pipe should reflect some sound back on itself to cancel more of it out.

Then you have those huge mufflers. Sized as they are even with those crazy straws they are getting exhaust from they only need to pass somewhat under 200 CFM each - my guess is they should handle more, ~250 CFM, each. They are not really taxed at all and should not present any significant restriction to the exhaust. As far as their construction goes, thinking about it, they are probably like the Maremont Cherry Bomb "Turbo" mufflers - more or less a conventional set-up. I seriously doubt there is any funky plumbing inside although it'd be nice to see becasue they were not light weight.

As far as what Chris Lombard is saying, I suspect the move to get a more muscluar sound from the Riv would be to LEAVE the resonator in place and put old-school Cherry Bomb or the relatively new design Hooker Maximum Flow mufflers in their place. If you put in Cherry Bombs--I suggest that you *not* weld them in, as you know they don't last very long. The resonator as it is gets rid of a sound (that is, gets rid of a tone not the volume per se) you probably don't want (no matter how loud you want the exhaust to be), and based on personal experience I'd leave it the heck alone.

I have to run

Albertj

PS whatever you do leave that @#*$&@(#* Resonator in there. Or put in a bigger one.

Albertj

crlombardi69 wrote:

Has anyone out there ever removed the resonator and left the factory mufflers or remove the mufflers and replace them with straight pipes w/nice tips??Wondering how this would sound without having to try it myself before I do my full custom exhaust because no exhaust companies see the value in offering us some systems.

I've been tempted to do exactly what you're talking about ever since I bought the car. The main reason I haven't, besides labor costs, is that it has been pretty well proven that you can never get a 90-degree V6 to sound that good out the back...


And Albert, quite a deep dissertation!

I know about the 90 deg. Engine sound but I kinda like it but on the other hand I don't want my luxury coupe to sound like a ricer piece of sh__!!

crlombardi69 wrote:

I know about the 90 deg. Engine sound but I kinda like it but on the other hand I don't want my luxury coupe to sound like a ricer piece of sh__!!

Exactly... Here's a green + for you!

crlombardi69 wrote:

I know about the 90 deg. Engine sound but I kinda like it but on the other hand I don't want my luxury coupe to sound like a ricer piece of sh__!!

Short answer:

If you leave the resonator in place you can get a nice muscular sound from a pair of 'performance' mufflers - flowmasters, vortex, what have you. I recommended Hooker Maximum Flow because of construction and flow data - they are stainless guts wrapped in aluminized steel shell, welded construction; they flow darn well and due to the case steel sound pretty mellow - I think if you do a web search you'll find sound clips *and* you'll find the flow data.

Albertj

Eldo wrote:

crlombardi69 wrote:

Has anyone out there ever removed the resonator and left the factory mufflers or remove the mufflers and replace them with straight pipes w/nice tips??Wondering how this would sound without having to try it myself before I do my full custom exhaust because no exhaust companies see the value in offering us some systems.

I've been tempted to do exactly what you're talking about ever since I bought the car. The main reason I haven't, besides labor costs, is that it has been pretty well proven that you can never get a 90-degree V6 to sound that good out the back...


And Albert, quite a deep dissertation!

data talks, BS walks. I hope you found the data informative.

Albertj

https://www.youtube.com/watch?v=SVWrcfp9QAM

Actually this is more like what you'll get:

https://www.youtube.com/watch?v=Qovin2FMfKg&feature=related

Albertj

Ok guys, my exhaust needs replacement. I first noticed a slight noise in the fall and now it a full blown rattle. Sounds like its coming from the catalytic covnerter. I am not sure if I can afford to replace the entire exhaust at the moment. The OEM lasted 14 years and I am planning to keep it all original, but I was wondering what type of material to use? I've been reading the thread and came across the part where you guys are discussing using 409, 304 or -321 metals. So when approaching a shop do I say, " I want a cat made of 304 metal?" What about material thickness? What brand equals OEM performance? Can you guys offer a recommendation?

A side question: What would the car sound like with a resonator but no mufflers? ( trying to save some bucks.)

if you live in Canada a full stainless is the way to go. dont forget to check the condition of your stock headers if you dont plan to replace also. the stock headers are prone to leaking around the header plates.

BMD wrote:

Ok guys, my exhaust needs replacement. I first noticed a slight noise in the fall and now it a full blown rattle. Sounds like its coming from the catalytic covnerter. I am not sure if I can afford to replace the entire exhaust at the moment. The OEM lasted 14 years and I am planning to keep it all original, but I was wondering what type of material to use? I've been reading the thread and came across the part where you guys are discussing using 409, 304 or -321 metals. So when approaching a shop do I say, " I want a cat made of 304 metal?" What about material thickness? What brand equals OEM performance? Can you guys offer a recommendation?

A side question: What would the car sound like with a resonator but no mufflers? ( trying to save some bucks.)

No mufflers with just a resonator is quite loud. It may be louder than you would like to hear. Now if you get rid of the resonator, and keep the mufflers, that changes the sound without getting crazy loud. Your typical stainless piping that good exhaust shops have will be fine. Getting anything better than that will definitely put a dent in the piggy bank.

BMD wrote:

Ok guys, my exhaust needs replacement. I first noticed a slight noise in the fall and now it a full blown rattle. Sounds like its coming from the catalytic covnerter. I am not sure if I can afford to replace the entire exhaust at the moment. The OEM lasted 14 years and I am planning to keep it all original, but I was wondering what type of material to use? I've been reading the thread and came across the part where you guys are discussing using 409, 304 or -321 metals. So when approaching a shop do I say, " I want a cat made of 304 metal?" What about material thickness? What brand equals OEM performance? Can you guys offer a recommendation?

A side question: What would the car sound like with a resonator but no mufflers? ( trying to save some bucks.)

First off it sounds like your not sure what is causing the noise. So a complete exhaust system is probably not necessary anyway.
Bring it to a shop for an estimate and a list of what it needs first.
The estimate is free, then report back with what it needs and we bounce around a couple of ideas.
Unless they have a fix for it that is reasonably priced and you want it done then go for it.
With our factory systems being Stainless Steel already, it's highly unlikely you need everything replaced.
BTW, the rattle could just be a heat shield that has come loose and tack welding could fix it. Don't know without looking at your exhaust system. Just pointing out it could be something inexpensive to have an Exhaust Shop fix.

Thanks for the info guys. I did get a ballpark figure at a local shop (not up on a hoist) and the price I got for the whole thing was $1600. Preferably, I would like to get it all done in one shot, because the mufflers are not in the best shape and look like they might be next although the pipes look good. But, I can't justify spending that much right now. I am thinking I will do the fron half, from the manifold to the resinator, then do the "Y" pipe mufflers and tips at a later date. I was definately thinking I would put stainless, but are there different quality levels to stainless? and what brands should I stay away from.

$1600?????? That's way over priced dude....I don't know about where you are, but we have shops here that will custom make the whole thing for less than half that.......

Ya thats really expensive!

No kidding! I could get an entirely custom stainless steel system from the headers back with good mufflers for $800.00 and I thought that was high.

Thanks for that info. I felt it was high aswell, the quote I got for just the cat was $300? I don't know what it is, but up here everything is more expensive! Anyway, what about some advice as far as name brand cats, resinators, mufflers? And I'm still wondering, is stainless steel stainless steel? or are there levels of stainless steel quality?

$300 for a cat is ok. That should be the most expensive part.
Example: I paid $65 each for my mufflers, $30 for my O2 simulator (cat delete), and a guy made my exhaust from the downpipe back for $150...this included the pipe.

As far as exhaust pipe goes, stainless is stainless. The only time I would pay attention to the grade is if and when you get custom tips. The GM tips I have are what I consider "true" stainless. I could let them get black and covered in salt all winter.....spray some cleaner on and the shit just runs off and they look like new. However, those type of tips are around $300 by themselves. Not sure of the exact number for the grade...I'd have to check.

So, including the cat with some mild aftermarket mufflers, you should be lookin at around $500 for a new exhaust, give or take $50.

$1600? Man I need to get back into the exhaust business. lol

Seriously, you could build a NICE stainless system for about $600 depending of course on mufflers. My new system will be about that price as I am going with stainless Spintechs and no cat. I've yet to find a muffler with their unique sound.

You could get it even cheaper if you can find a shop capable of mandrel bending stainless instead of crush bending. Then you can buy the sticks yourself and save some coin.

http://www.dynomax.com/mufflers.php?muffler=vt

This looks pretty promising at least in theory. It'll be availalbe soon.
If it's managably priced, I'll try it out.