Making a muffler

[pdq67]

I am 99.99% sure those scoops inside the straight through mufflers are not helpful to max airflow. I ran glasspacks in the 80's and made more power with turbo style mufflers. Less issues with neighbors too.

WDT glass packs don't have anything protruding into the gas stream.

They are smooth, perforated inner pipe jobbers!

That's why I like them!!

Cherry-Bombs and Smitties as well as Purple Hornies, they have sawed louvers in them that protrude into the middle of them if not mistaken?..

pdq67

[ptuomov]

I am 99.99% sure those scoops inside the straight through mufflers are not helpful to max airflow. I ran glasspacks in the 80's and made more power with turbo style mufflers. Less issues with neighbors too.

WDT glass packs don't have anything protruding into the gas stream. They are smooth, perforated inner pipe jobbers!
That's why I like them!! Cherry-Bombs and Smitties as well as Purple Hornies, they have sawed louvers in them that protrude into the middle of them if not mistaken?..

Don't most contemporary performance mufflers such as Magnaflow race mufflers and Borla XR-1 Sportsman mufflers essentially already incorporate all the features of a glass pack muffler, as they have similar packing material? Except they also have the larger case which functions as an expansion chamber muffler in addition to the glass pack?

[hoffman900]

I am 99.99% sure those scoops inside the straight through mufflers are not helpful to max airflow. I ran glasspacks in the 80's and made more power with turbo style mufflers. Less issues with neighbors too.

WDT glass packs don't have anything protruding into the gas stream. They are smooth, perforated inner pipe jobbers!
That's why I like them!! Cherry-Bombs and Smitties as well as Purple Hornies, they have sawed louvers in them that protrude into the middle of them if not mistaken?..

Don't most contemporary performance mufflers such as Magnaflow race mufflers and Borla XR-1 Sportsman mufflers essentially already incorporate all the features of a glass pack muffler, as they have similar packing material? Except they also have the larger case which functions as an expansion chamber muffler in addition to the glass pack?

Kind of. It's just the ID is the same as the id of a smooth pipe. The Coast Fab/Burns mufflers are the most expensive, but the best.

[MadBill]

Well the purpose of a muffler is reduce acoustic energy output, and those methods have been touched on here in numerous responses, but that acoustic energy is normally converted into heat, and if your alum muffler is effective, it won't be for long, as it starts to drip alum.

Here's an empirical question that is relevant for the dimension calculations. Does exhaust gas heat or cool as it goes thru a muffler? I always assumed that outlet was cooler than inlet, but "assume makes an a$$ out of u and me" as they say.

It cools due to heat transfer into the exhaust pipes and mufflers, proportional to internal turbulence, surface area, airflow over the system's exterior, etc. Just for interest I might see if I still have enough thermo-couple wire to plumb my T/C read out into different parts of the system..

Due to chemical activity, exhaust temperature does rise during its passage through a catalytic converter.

[wyrmrider]

I've used bot bullets and turbos at the end of a tailpipe for additional sound control-- both work at different frequencies
turbo's take more room
good idea above to use pipe like the Corvette side pipe dented tubes
a turbo should quiet things down
what- no catalyst?

[ptuomov]

what- no catalyst?

Theoretically able to run either dual Magnaflow 3.5" I/O 5" core cats or, more likely 3.5" I/O "test pipes" when running on race gas and actually needing the flow capacity of 3.5" exhaust. Cats vs. test pipes can be swapped relatively easily with v-band clamps, provided that someone didn't forget to put that anti-seize on...

[ptuomov]

The Coast Fab/Burns mufflers are the most expensive, but the best.

The best because of the light weight or the best because of back pressure vs. case volume vs. muffling performance? I don't really care about the weight that much here, but I do care about getting a low back pressure and good muffling performance from the given space.

[j-c-c]

Well the purpose of a muffler is reduce acoustic energy output, and those methods have been touched on here in numerous responses, but that acoustic energy is normally converted into heat, and if your alum muffler is effective, it won't be for long, as it starts to drip alum.

Here's an empirical question that is relevant for the dimension calculations. Does exhaust gas heat or cool as it goes thru a muffler? I always assumed that outlet was cooler than inlet, but "assume makes an a$$ out of u and me" as they say.

It cools due to heat transfer into the exhaust pipes and mufflers, proportional to internal turbulence, surface area, airflow over the system's exterior, etc. Just for interest I might see if I still have enough thermo-couple wire to plumb my T/C read out into different parts of the system..

....

That would be assuming the acoustic energy conversion to heat is less then the heat transfer to the surroundings. To the original question of hotter vs cooler, I don't know, but there are a lot of variables between applications, ambient air flow, engine output at the momenta of heat measurement etc. I'm sure if we dig far enough it has been studied and documented..

[hoffman900]

The Coast Fab/Burns mufflers are the most expensive, but the best.

The best because of the light weight or the best because of back pressure vs. case volume vs. muffling performance? I don't really care about the weight that much here, but I do care about getting a low back pressure and good muffling performance from the given space.

The Magnaflows and Borla perform as well, but they're light and rebuild able, so that's a huge plus for many.

[ptuomov]

Thanks for the long post.

Some things we learned and ran up against......

* Allow end of collectors to extend 2" to 3" into termination chambers. Same for exit pipe at opposite end.

* Ideally, you want each termination chamber to have volume equal to twice the displacement discharged into it. More doesn't hurt and even if you cannot get more than 75%, its worth the effort.

* Entire interiour volume of termination chamber (less volume taken up by entry and exit pipe stubs extending into chamber at either end) counts towards necessary volume.

* Muffler(s) should be located downstream of chambers (can be directly behind chambers or anywhere between ends of chambers and ends of exhaust system.

* Chambers can have round, oval, square or rectangular cross section. And a square cross section of same size as a round cross section will obviously have greater interiour volume for same length. However...... In actual practice, we found straight sided (square or rectangular) chambers of same wall thickness are more likely to flex, work harden and be affected by metal fatigue over time than round or oval cross sections.

* Final configuration...... We pulled round termination chambers and hand drilled beaucoup 3/16" diameter holes in them (360 degrees on 3/4" spacing to within 1" of each end). This took a while and was no fun at all. When done, we made new end caps (like large flat washers) to accommodate larger outer shell 7" in diameter, slid one over front stub and welded it in place, leaving original cap and the tubing we had drilled in place. Slid outer shell over tubing that we drilled and welded outer shell to front end cap. Then went to a machine shop where they had lots of stainless steel shavings they had saved for us and packed them into the annular space between tubing we drilled and new outer shell using a piece of 3/4" square bar stock a couple of feet longer than our new outer shell. Once we had it packed tight in each, we slid the washer shaped rear end cap piece over stub and welded it in place. The end result was that we made our termination chambers double as straight through steel packs in addition to the DynoMax Super Turbo mufflers we already had just ahead of rear bumper. These DynoMax mufflers were sized for flow and gave us the 2.2 cfm per HP recommended by David Vizard for zero sum loss muffled exhaust system. It was still pretty throaty when you got on it but was quiet enough not to drive you nuts on long trips and not loud enough to draw unwanted attention from police.

* Crossover (balance) pipes connecting left and right bank...... We found no advantage between 'X' type and 'H' type so long as 'H' type was same size as collectors. Crossover pipe can be placed anywhere after primaries enter collectors and it can even be placed between termination chambers if you wish. We placed ours about 6" behind front of termination chambers. Later added a 2nd crossover joining left and right side tailpipes behind chambers in area just before top of bend going over rear axle. Each crossover pipe seemed to help lower noise level a bit and smoothed out exhaust note some, as well.

* One thing we found on chassis dyno regarding full length muffled exhaust was that if your pipe size is sufficient for power generated but you cannot get flow you need through mufflers any other way...... By using tube size increasers/reducers (like a bell reducer), if you install free flowing mufflers having one size larger internal flowpath than pipe system size...... They will flow same as if you ran straights (no mufflers). But they will be louder than mufflers same size as pipe system.

It seems to me that the extending the pipe inside the expansion chamber changes the frequency response in a major way. The simple expansion chamber gives a transmission loss that even I can kind of understand intuitively.

SimpleExpansionChamber.png

Expanding the pipe inside the expansion chamber seems to retain some of the weak spots of the shorter chamber, but there's now an extra frequency that gets muffled really well:

LongerChamberWithExtendedInlet.png

Somehow pipe extension into the expansion chamber that is 1/3 of the total chamber length resulting in 2/3 of free chamber length before outlet really kills that one frequency extremely well.

I'm not sure if we should think about the volume of the chamber or think about the length and the diameter separately. I'm currently thinking that the length detemines what frequencies the expansion chamber muffles and the diameter how much it muffles them. More specifically, I think that h=(m-1/m)^2 where m is the inlet area (in this case the same as outlet area) divided by the chamber cross-sectional area is the measure that seems to drive the magnitude of muffling. So bigger pipe needs a bigger can (shocker there).

One question is that if you have a 3" pipe and run that to a perforated core with 5" diameter and then put that inside a 7" pipe with fiberglass or stainless shavings packing, does the sound wave see that more as a 5" diameter expansion chamber or as a 7" diameter expansion chamber?

[j-c-c]

"Somehow pipe extension into the expansion chamber that is 1/3 of the total chamber length resulting in 2/3 of free chamber length before outlet really kills that one frequency extremely well. "

I believe part of the basis for this is similar to the placing of a stereo speaker, speaker output dramatically rises as a speaker is moved closer to surface/wall. ceiling, corner, etc The extension mentioned above, effectively "decouples" the sound wave from the nearby surface, it is as we have already toyed with, distance/frequency dependent.

Another assumption worth noting in this discussion, it it usually stated with our engines, 1/3 of consumed energy becomes work/hp, 1/3 waste heat, radiant, radiator, etc and 1/3 acoustic energy.

[ptuomov]

"Somehow pipe extension into the expansion chamber that is 1/3 of the total chamber length resulting in 2/3 of free chamber length before outlet really kills that one frequency extremely well. "

I believe the basis for this is similar to the placing of a stereo speaker, speaker output dramatically rises as a speaker is moved closer to surface/wall. ceiling, corner, etc The extension mentioned above, effectively "decouples" the sound wave from the nearby surface, it is as we have already toyed with, distance/frequency dependent.

Here's one verbal explanation of it that I found somewhat illuminating:

https://www.acoustics.asn.au/conference ... ers/34.pdf

"Similar to a standard expansions chamber is the extended inlet and outlet expansion chamber, where the inlet and outlet tubes are extended into the expansions chamber... The benefit of such a design is that part of the chamber between the extended pipe and the sidewall acts as a side branch resonator therefore improving the transmission loss. The greater the protusion into the muffler the greater the transmission loss however the inlet and outlet tubes should maintain a separation space of at least 1.5 times the diameter of the chamber to enure the decay of evanescent modes."

That's very clear except the words "enure" and "evanescent" which I had to google!

[pcnsd]

Thanks for the long post.

Some things we learned and ran up against......

* Allow end of collectors to extend 2" to 3" into termination chambers. Same for exit pipe at opposite end.

* Ideally, you want each termination chamber to have volume equal to twice the displacement discharged into it. More doesn't hurt and even if you cannot get more than 75%, its worth the effort.

* Entire interiour volume of termination chamber (less volume taken up by entry and exit pipe stubs extending into chamber at either end) counts towards necessary volume.

* Muffler(s) should be located downstream of chambers (can be directly behind chambers or anywhere between ends of chambers and ends of exhaust system.

* Chambers can have round, oval, square or rectangular cross section. And a square cross section of same size as a round cross section will obviously have greater interiour volume for same length. However...... In actual practice, we found straight sided (square or rectangular) chambers of same wall thickness are more likely to flex, work harden and be affected by metal fatigue over time than round or oval cross sections.

* Final configuration...... We pulled round termination chambers and hand drilled beaucoup 3/16" diameter holes in them (360 degrees on 3/4" spacing to within 1" of each end). This took a while and was no fun at all. When done, we made new end caps (like large flat washers) to accommodate larger outer shell 7" in diameter, slid one over front stub and welded it in place, leaving original cap and the tubing we had drilled in place. Slid outer shell over tubing that we drilled and welded outer shell to front end cap. Then went to a machine shop where they had lots of stainless steel shavings they had saved for us and packed them into the annular space between tubing we drilled and new outer shell using a piece of 3/4" square bar stock a couple of feet longer than our new outer shell. Once we had it packed tight in each, we slid the washer shaped rear end cap piece over stub and welded it in place. The end result was that we made our termination chambers double as straight through steel packs in addition to the DynoMax Super Turbo mufflers we already had just ahead of rear bumper. These DynoMax mufflers were sized for flow and gave us the 2.2 cfm per HP recommended by David Vizard for zero sum loss muffled exhaust system. It was still pretty throaty when you got on it but was quiet enough not to drive you nuts on long trips and not loud enough to draw unwanted attention from police.

* Crossover (balance) pipes connecting left and right bank...... We found no advantage between 'X' type and 'H' type so long as 'H' type was same size as collectors. Crossover pipe can be placed anywhere after primaries enter collectors and it can even be placed between termination chambers if you wish. We placed ours about 6" behind front of termination chambers. Later added a 2nd crossover joining left and right side tailpipes behind chambers in area just before top of bend going over rear axle. Each crossover pipe seemed to help lower noise level a bit and smoothed out exhaust note some, as well.

* One thing we found on chassis dyno regarding full length muffled exhaust was that if your pipe size is sufficient for power generated but you cannot get flow you need through mufflers any other way...... By using tube size increasers/reducers (like a bell reducer), if you install free flowing mufflers having one size larger internal flowpath than pipe system size...... They will flow same as if you ran straights (no mufflers). But they will be louder than mufflers same size as pipe system.

It seems to me that the extending the pipe inside the expansion chamber changes the frequency response in a major way. The simple expansion chamber gives a transmission loss that even I can kind of understand intuitively.

SimpleExpansionChamber.png

Expanding the pipe inside the expansion chamber seems to retain some of the weak spots of the shorter chamber, but there's now an extra frequency that gets muffled really well:

LongerChamberWithExtendedInlet.png

Somehow pipe extension into the expansion chamber that is 1/3 of the total chamber length resulting in 2/3 of free chamber length before outlet really kills that one frequency extremely well.

I'm not sure if we should think about the volume of the chamber or think about the length and the diameter separately. I'm currently thinking that the length detemines what frequencies the expansion chamber muffles and the diameter how much it muffles them. More specifically, I think that h=(m-1/m)^2 where m is the inlet area (in this case the same as outlet area) divided by the chamber cross-sectional area is the measure that seems to drive the magnitude of muffling. So bigger pipe needs a bigger can (shocker there).

One question is that if you have a 3" pipe and run that to a perforated core with 5" diameter and then put that inside a 7" pipe with fiberglass or stainless shavings packing, does the sound wave see that more as a 5" diameter expansion chamber or as a 7" diameter expansion chamber?

Because sound attenuation is an area of concern for me and also because of my general habit of collecting equations, I have a couple of questions regarding the equations posted.
In the first posted equation H=(M-1/M)^2, I would like to confirm H is the frequency in Hertz. A description of M was given as M= inlet CSA/Expansion area CSA
In the equation quoted above what is 'kl"?

Thanks,
Paul

[ptuomov]

Because sound attenuation is an area of concern for me and also because of my general habit of collecting equations, I have a couple of questions regarding the equations posted.
In the first posted equation H=(M-1/M)^2, I would like to confirm H is the frequency in Hertz. A description of M was given as M= inlet CSA/Expansion area CSA
In the equation quoted above what is 'kl"?

H is not Hertz. It's my simple measure of muffler effectiveness. It multiplies everything inside the 10*log10(1+x) function. It doesn't determine the frequency, instead it determines how much sound pressure reduction there is across the board, scaling the transmission loss function.

l is the length of the muffler case or the expansion chamber. k is a function of frequency, speed of sound.

But don't take my word for any of this, reading this thread should leave nobody any uncertainty about the fact that I don't yet understand any of this.

[pdq67]

Harry,

In all respect, just install the old WDT smooth perforated inner pipe glass packs and go!!

Too loud, then add either two, "y'd", side by side OR another behind each and go.. AND with tailpipes out past the rear bumper!!

I had three glass packs under each side of my old hopped up 409 so know!!

pdq67