1 2
67LS1
67LS1 New Reader
6/6/21 9:04 p.m.

I got my Super Turbo Mufflers and am going to install them as soon as I get another project off the lift.

But I just read a couple of different articles that also mentioned that X pipes tend to sound more raspy and H pipes tend to lower the tone. I got from the articles that this was pretty common knowledge. 
I'd never heard this and am wondering if any of you have.
If I'm going to make a change now would be the time.

 

malibuguy
malibuguy HalfDork
6/8/21 9:11 a.m.

In reply to 67LS1 :

its true...but there is small differences...an "open" Xpipe like the cheap stamped ones do not quite have the higher pitched tone as say a merge style Xpipe.

As I would say to customers Xpipes help make the car sound a little more exotic and good merge one makes it sound like your revving higher then you actually are.

Here is an example of a tighter X I did on a Silverado many years ago.  He wanted emphasis on midrange torque.  The beauty of Xpipes is you can really shape the power curve to suit the customers needs.

pres589 (djronnebaum)
pres589 (djronnebaum) UltimaDork
6/8/21 11:14 a.m.

I think it's really hard to make generalized statements about this kind of thing.  There's probably not a lot of OHC V6 engines out there paired with an H-pipe based exhaust system so finding examples to review is going to be tough.  

67LS1
67LS1 Reader
12/3/21 8:26 p.m.

Update:

I replaced the QFlll's with the Dynomax Super Turbos (20" case). I did not change out the X pipe and I'm still running 2.5" tailpipes all the way to the bumper.

It's better but it still "drones" at part throttle/slight load. I put "drones" in quotation marks because I'm not 100% sure it's drone but it's super annoying. It's a low "bawww" sound. 

I've got maybe 1k miles on it since the change and the more I drive it the more it feels like the noise is coming from under my feet, so way forward of the mufflers. Like right after the cats. BTW, the outlet of the cats are directly into a 45 and then approx. 25" of straight pipe be fire 45ing towards the X. 

Would resonators right after the cats help any?

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
12/3/21 9:23 p.m.

In reply to 67LS1 :

Yes, a lot.

malibuguy
malibuguy HalfDork
12/5/21 6:20 p.m.

Depends on the resonator.

Most things advertised as "resonators" are essentially small mufflers and do not typically do much for drone as they typically are effective at frequencies much higher then your typical drones...which normally fall in the 90-130hz range.  Most of the small mufflers or glasspacks if you will act more as a low-pass filter.  Reducing or eliminating higher frequencies while letting the low frequencies pass thru essentially unaltered.

What I find is most exhaust systems tend to have 2 drone frequencies...one that will resonate with firing frequency of the driveline and then a system resonance that is independent of that.

Knowing how typically SuperTurbos behave in most cars you probably have a firing resonance that will easily be addressed with a 1/4 wave resonator or a helmholtz resonator.

1/4 wave resonators are the easiest to fit most times.  However I find helmholtz resonators to be more effective.

67LS1
67LS1 Reader
12/27/21 10:12 a.m.

Bringing this back because I just found an old pic I have a question about.

When I was doing my swap I was told the second canisters on the exhaust down pipes were secondary cats and unnecessary. So I cut them off and added lengths of straight pipe to connect from just below the 2nd O2 sensors to the Pypes exhaust system.

Looking back now, did I just cut off and dispose of the stock Camaro resonators? Is this the root of my horrendous sound issue? Am I an idiot?

Please don't answer the last question...

 

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
12/27/21 10:57 a.m.

They are secondary converters, but the cross section area changes may have contributed to drone reduction by removing exhaust energy, maybe.

 

Without knowing the math involved, I wonder if you could use a crossover pipe  blocked off in the middle to act as a stub for each side.

Mr. Peabody
Mr. Peabody UltimaDork
12/27/21 11:31 a.m.

The secondary cats would have definitely made your exhaust quieter and reduce the drone you're now experiencing.

 

 

 

67LS1
67LS1 Reader
12/27/21 5:43 p.m.

I just feel like a resonator will attenuate a (slightly) wider spectrum of drone than a 1/4 wave or Helmholtz resonator. Especially if I had to rely on a simple cell phone analyser and my math skills. So I guess I'm going to add a couple Vibrant resonators right after the cats. I have about 13" from the vertical part of the down pipe to the crossmember so I think they'll fit. I'm hoping the Ultra Quiet (#1141) will clear the transmission otherwise I'll go with the bottle shaped ones (#1792).

The bottom of the transmission pan in this photo is ABOVE the front K member so I'm not happy that whatever resonator I add will hang lower.

Any value in changing out all of the stock style hangers (4) to the newer style with the rubber donuts?

alfadriver
alfadriver MegaDork
12/27/21 7:27 p.m.

Late to this party- but to those who are experienced in exhaust sound in new engines compared to old- is the droning because of two exhaust valve sound ever so slightly off vs. one big one?  I may be interpreting the sound wrong, but it sure seems that I hear a drone like sound more often on modern 4V engines than older 2V engines.  

Not that it helps much...  

Did you try the single exhaust?

67LS1
67LS1 Reader
12/28/21 3:03 a.m.
alfadriver said:

Late to this party- but to those who are experienced in exhaust sound in new engines compared to old- is the droning because of two exhaust valve sound ever so slightly off vs. one big one?  I may be interpreting the sound wrong, but it sure seems that I hear a drone like sound more often on modern 4V engines than older 2V engines.  

Not that it helps much...  

Did you try the single exhaust?

Yeah, I get it. I'm not 1000% sure if it's drone or rasp or some weird engine related harmonic but it's annoying as hell.

The only single exhaust attempt I've tried was block off one leg at the tail pipe. So the X pipe, second muffler, etc, we're all still there. 

alfadriver
alfadriver MegaDork
12/28/21 9:36 a.m.

So the next attempt is to put a resonator where the second catalysts were?  

It will be interesting to hear what the results are....

Mr. Peabody
Mr. Peabody UltimaDork
12/28/21 9:45 a.m.

It will be better. How much will depend on the quality of the resonator

malibuguy
malibuguy HalfDork
12/29/21 6:36 p.m.

your hangers are fine as along as there is proper isolation, most hangers are fine.  However the more compliant the better ultimately.

the 2ndary cats will definetly make a difference but its not world changing, they would of slowed & softened the note slightly.  cannot comment if they would of changed drone characteristics, usually they do not.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
12/29/21 10:29 p.m.

 thought I had replied to this the last time around, but I guess I didn't.

Your exhaust tubing is like a Tuba.  The sound pulses from the engine are your lips in the mouthpiece.  By manipulating the valves, you change the natural resonance frequency of the tubing into one set of overtone series.  The muffler is like a cotton ball somewhere inside the tuba.  The sound waves approach the cotton ball and get attenuated because of the state change.  Sound doesn't do change well.  If you put the cotton ball directly in the middle of the total length of the tubing (a Tuba is about 16'), it will have the least affect on attenuating sound because the 8' before the cotton ball is the same length as the 8' after.  The sound that does make it through the cotton will continue to be supported by the fact that there is another 8' of tubing that is tuned to the same note that is on the other side of the cotton.  Sliding the cotton ball out to say 10' will cause an imbalance, and fewer frequencies that are supported by the resulting unequal length of the tubing on either side of the cotton.  This is why mufflers aren't usually in the middle between the tailpipe and engine.  They're usually further back.

This drone you get is caused by what is called a standing wave frequency.  You've probably all experienced it in the shower or a closet or in a bathroom.  There is one set of frequencies that when you hit it, it sounds like the walls just closed in on your ears.  Loud and boomy.  That frequency is directly dependent on the distance from your ears and the walls.  It happens when the wavelength of the frequency matches the distance.  Try it sometime.  Find the frequency that resonates and then move your head closer to one wall.  The boomy-ness reduces because you're not in the center where the standing waves are colliding and giving your ears more gain.

Drone from standing waves can usually be solved (or changed) by moving the mufflers fore and aft so that what would be a standing wave frequency for the leading section of pipe would not be a standing wave frequency after the muffler.  Without doing some serious calculations,  you run the risk of just changing where the drone is in the RPM band, but worth a shot.  Turn-down tips can make drone worse.  If you set up a reflected sound under the trunk, when you reach the frequency that becomes a standing wave between the ground and the trunk pan, the trunk pan just vibes sympathetically with the sound.  This can be fixed by not doing turndowns, or by altering the resonance frequency of the trunk pan (which is exactly what Dynamat does)

General rules:  Larger tubing = louder and lower rumble.  More bends = quieter but more restrictive.  Smaller tubing = Quieter and higher frequency (think of an old beetle with the Pea Shooter exhaust).  Baffled mufflers (like a Flowmaster) without packing material can alter the sound waves and be effective, but they are fixed distances and angles while the engine is throwing all kinds of frequencies at them.  A packed muffler tends to be better and knocking down the high frequencies and keeping the lows.  Larger muffler volume = more overall attenuation

I think a resonator would help a good bit.  They're kind of like an oversized muffler.  Think of them kinda like the aerator on your kitchen faucet.  Right at the end, they take a stab at grabbing and foiling some of the frequencies.  The point is to put them as close to dead last in the system with the least amount of tailpipe after them.

67LS1
67LS1 Reader
12/30/21 4:00 a.m.

Aarrgghhhh....I was planning on putting them just after the cats, where the secondary cats were. The thought being that it really feels like the drone/harshness is right under my feet.

There's a lot of pretty straight piping forward of the mufflers on this car.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
12/30/21 10:06 p.m.

The origin of the drone is almost never where the drone actually is.  Like in my example of singing in the shower/bathroom, the source of the drone is wherever the standing wave hits your ears.  It's like hearing thunder when you're inside your house.  You can't say, "that came from the south east."  Or when you're listening to four Tubas in a band concert.  You can't tell which ones are playing the Bb and which ones are playing the F.  You just hear the whole mix of all the frequencies.

Unfortunately for you, you don't have the millions of dollars that OEMs used to R&D their exhaust, so it's trial and error.  You might eliminate the drone by putting them immediately after the cats.

Other things you can try that don't involve lots of work:

  • Take a chunk of heavy steel angle and a couple hose clamps.  Strap it on the tubing somewhere.  Did the drone change?  If it did, you might just be getting vibratory noise.  The tubing itself might be buzzing like a guitar string.  Changing the weight (adding the steel) changes it's natural vibe frequency to something else.  If you find a magic spot where the steel is making the drone go away, just add another rubber isolation mount at that point.
  • Take a piece of something soft; a mattress topper, an anti-fatigue rubber floor mat, a memory foam bath mat and put it in the cargo areas - rear seat well, trunk floor, etc.  Set something heavy on it... a couple cylinder heads, a battery, or some flooring tiles.  Drone go away?  You might just be getting sympathetic vibes causing the body panels on the car to vibrate at certain frequencies.  Dynamat, undercoating, or some other way of damping and changing the sympathetic frequencies at which they vibrate can help.  My 96 Impala SS with a Dynomax cat-back had a pretty good drone at around 2300... unless I had the trunk full on the way back to college, then the drone went away.  I cut out some 1/2" MDF and glued it to the trunk pan and covered it with carpet.  Problem solved.

Keep this in mind, though... You are simply trying to change things.  There is no real predictable thing here.  Acoustics are berkeleying wild.  All of these are simply ways of finding what is causing the drone and then just changing the physical properties one way or the other.  You might fix it, you might make it worse, you might just move the drone to another RPM.

Above all, you can't really take advice about what worked in someone else's car any more than you can compare what worked in Carnegie Hall and hope it works in your living room.  Most of the time at the shop, we just kept trying different mufflers until the problem went away.  Of course, we were a higher-end custom shop, so we had plenty of random mufflers lying around.  Of course we had pretty well-known recipes; Cammed LS gets a Magnaflow unless it has headers, then it gets a Dynomax, that kind of thing.... but 425 Nailhead in a 51 Merc with a custom interior and a chopped, sectioned, and channeled body?  There really isn't an internet forum full of knowledge for that.

Just try stuff.  The couple things on the list above will at least eliminate the simple stuff first before you go nuts with exhaust changes only to find out it was vibes from the trunk pan all along. 

67LS1
67LS1 Reader
12/31/21 4:31 a.m.

I'm 99.9% sure it isn't body metal. The car has Dynomat pretty much everywhere. I'll try clamping some metal to different sections of pipe.

1 2
Our Preferred Partners
TvARNgEZ4Aaqt7i2p2IYaAF0VKdrrl09TirqOE9XOhC7qGqTI5Ovy0zWYiiyxmMz