Making a muffler

[ptuomov]

I found this old document very useful in explaining how these different muffler/resonator combinations work:

https://crgis.ndc.nasa.gov/crgis/images ... fflers.pdf

Thank you for this link. I know you already have a plan in hand for your project but if you don't mind I'd like your opinion on an extension of my tubes within tube idea. In the naca report they characterize expansion chamber mufflers based on the ratio between chamber diameter and inlet tube diameter, with bigger ratios yielding more attenuation. Any idea if this would still hold for multiple inlet tubes in parallel? My idea is to fill a 3" inlet tube with 1/2" ID tubes, with these tubes 3 to 5 diameters long so 1.5-2.5" long, with the ends of the tubes in the plane of the flat endplate that begins the expansion chamber. If that chamber ID is 6" this gives a ratio of 2 without the tubes and 12 with the tubes. Without the tubes the attenuation would be minimal, much less than 10 dB, but with the tubes the attenuation should approach 20 dB. Keeping the expansion chamber short extends the upper cutoff frequency so I think 6" would be best so start the divider wall to the next chamber 6" from the endplate, and make this divider wall from another bundle of 2.5" long 1/2" ID tubes, then follow that with another 6" long chamber to the flat end wall with 3" tubing in the center as the exit. This two chamber muffler should give 30+ dB of attenuation and I think should have minimal backpressure. There will be flow through the 1/2" ID tubes, and also some flow in the gaps between the tubes which will act like smaller diameter tubes for even more attenuation. The divider wall should have minimal restriction since it has 4x the open area, so the primary restriction will be the entrance bundle of tubes. If this proved too much a larger ID tube could be used here (3/4"?), and maybe a third chamber added. This could also be done using an oval shaped chamber which would probably give more attenuation. I know a drawing would be good, but think of this as a 2 or 3 chamber muffler 14 in Fig 11 with the chamber length as in muffler 5 in Fig 9. I admit this is basically intellectual curiosity on my part, but one thing they stress in the paper is that resonators don't work well with high flows and sound pressure levels so my idea might be a possibility to replace your Borla first stage mufflers before your custom resonator. Thoughts, boos, catcalls ?

I think that it's not the ratio of diameters that matters. It's the ratio of areas. The case end plate area to the inlet pipe area (=outlet pipe area) or m. So if you have 50mm diameter inlet pipe and 150mm diameter case, you have m=9. If you have the same 150mm case diameter and two 35mm inlet pipes that both have the same sound coming in, then you again have m=9.

[ijames]

Without knowing much about acoustics, I was taking the fact that a bigger dia tailpipe tip is louder than a smaller one and thinking of this as an expansion chamber where the chamber is some form of "acoustic diameter" around the tip so the reason it gets louder is that the ratio is changing, and then adding the Borla marine muffler tip with the bundle of small tubes inside the tip that people said did make it quieter than a plain tip that size, and hoping . I guess I either need to build a test fixture or go find an acoustics guy to ask.

[ptuomov]

Without knowing much about acoustics, I was taking the fact that a bigger dia tailpipe tip is louder than a smaller one and thinking of this as an expansion chamber where the chamber is some form of "acoustic diameter" around the tip so the reason it gets louder is that the ratio is changing, and then adding the Borla marine muffler tip with the bundle of small tubes inside the tip that people said did make it quieter than a plain tip that size, and hoping . I guess I either need to build a test fixture or go find an acoustics guy to ask.

Inserting a large number of smaller perforated pipes inside the main pipe may help, especially if it's within a muffler that has an expanded perforated core pipe and absorptive packing. This is roughly what those Borla multicore mufflers do:

IMG_0004.JPG

Since Borla does it, it probably helps a little. They are neither idiots or frauds there.

It will however not change the basic expansion chamber math that the area ratio determines the magnitude of the attenuation and length the frequencies. It's very hard to make a small muffler quiet.

[ptuomov]

John Kuhn is mocking up the tailpipe extension from the rear muffler. I think it looks good, and the angle is functional.

IMG_0012.JPG

IMG_0011.JPG

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[ptuomov]

Here's the wastegate dump pipe cone transition (the smaller pipe).

WastegateDumpPipeTransition.jpg

The wastegate dump pipe will act as a quarter wave resonator when the wastegate is closed. For it to be as effective as possible, the diameter should be large. The pipe steps up to 2" very soon after the wastegate which is the largest size that will fit. The flow is not critical in this pipe as 1.75" is already flowing just fine all the exhaust gas that the pipe needs to flow, hence the steep transition. In contrast, for the main downpipe from the turbine where high flow is the priority, the transition is very gentle. You can barely see the cone angle in the big pipe.

[pdq67]

OK, I'm back!

I have a 2.5" x 18" long and a 2.5" x 12" long way old school JCW turbo mufflers on my car down each side now that exit like stock. ('67SS/RS Camaro car here)... The long one under my front seat and the short one where the stock resonator fits.. This was behind my, "Strong Arm", 406 and I kept it for my 496!!

I want to change to the WDT, smooth perforated inner pipe glass packs by say installing a long and a short pair of them split going in and then gathered together going out down both sides, then to transverse glass packs right behind my rear end?? Exiting like stock.

Dave V., where are you at??

pdq67

[ptuomov]

OK, I'm back!

I have a 2.5" x 18" long and a 2.5" x 12" long way old school JCW turbo mufflers on my car down each side now that exit like stock. ('67SS/RS Camaro car here)... The long one under my front seat and the short one where the stock resonator fits.. This was behind my, "Strong Arm", 406 and I kept it for my 496!!

I want to change to the WDT, smooth perforated inner pipe glass packs by say installing a long and a short pair of them split going in and then gathered together going out down both sides, then to transverse glass packs right behind my rear end?? Exiting like stock. pdq67

Do you have photos? How much power does the car make?

I am not sure whether you're seeking opinions or what, but if you are, I'm interested in hearing what your objective is with these changes?

[n2xlr8n]

Great thread, BTW.

I'm in the middle of designing exhaust for my Ford Ranger 2.3 turbo.

So far I have a very gentle radius 3" DP from my 12cm housing to 3" exhaust to a 16" long round ultraflow. Not yet sure how I'm going to get rid of the low freq without hurting power.

Feel free to comment.

Thanks for the info.

[ptuomov]

Great thread, BTW. I'm in the middle of designing exhaust for my Ford Ranger 2.3 turbo. So far I have a very gentle radius 3" DP from my 12cm housing to 3" exhaust to a 16" long round ultraflow. Not yet sure how I'm going to get rid of the low freq without hurting power. Feel free to comment. Thanks for the info.

The most certain way to get rid of the low frequencies is to use a longest possible muffler or resonator upstream of the rear muffler. If a long muffler doesn't fit, then the next choice would be a muffler with a built-in Helmholtz resonator chamber. Another option is to run a very large divorced wastegate dump pipe and determine the length before the merge to the main exhaust based on quarter-wave resonator math. How much power is this thing expected to make? Do you have photos of your setup and the space available?

[n2xlr8n]

Great thread, BTW. I'm in the middle of designing exhaust for my Ford Ranger 2.3 turbo. So far I have a very gentle radius 3" DP from my 12cm housing to 3" exhaust to a 16" long round ultraflow. Not yet sure how I'm going to get rid of the low freq without hurting power. Feel free to comment. Thanks for the info.

The most certain way to get rid of the low frequencies is to use a longest possible muffler or resonator upstream of the rear muffler. If a long muffler doesn't fit, then the next choice would be a muffler with a built-in Helmholtz resonator chamber. How much power is this thing expected to make? Do you have photos of your setup and the space available?

Boport stg 3 iron D port turbo head, 2.1 cam (specs unpublished, but I have them), 9:1, MS3x with D585 LS coils. Mighty Mouse C4 with brake, PTC 10" 4500 with 3.73s (not enough, but it won't make more than a dozen track passes).

Honestly, if it doesn't make ~475 whp on E85, I'm officially retired from building cars...or putting a LS in it.

Plenty of photos, but not online yet- I'll post links tonight.

Tons of space under there, but not towards the rear suspension and cell - I didn't do a good job of planning for tail pipes.

[ptuomov]

A general question to people with muffler making experience:

I want a two-layer packing for the muffler. There will be a conical perforated sleeve that joins 2x3.5" to 1x4.5" tubes. This conical perforated sleeve will be surrounded by packing. I want the inner layer from high-temperature stainless steel woven mesh or something like that will not blow out no matter what. This is probably the easiest to cut from a sheet to a shape that wraps easily around the sleeve. Then, outside that layer, I want a layer that fills the rest of the muffler case. For this outer layer, I want the maximum corrosion resistance and maximum sound absorption. Some kind of ceramic or rock wool packing might work well. There will be a small drain hole at the bottom of the end plate let the acid water leak out when the muffler cools. The weight is not a concern here, can be heavy (and maybe should be heavy to absorb sound better).

Question: Any specific materials and/or sources you've personally used and that can recommend?

[pcnsd]

A general question to people with muffler making experience:

I want a two-layer packing for the muffler. There will be a conical perforated sleeve that joins 2x3.5" to 1x4.5" tubes. This conical perforated sleeve will be surrounded by packing. I want the inner layer from high-temperature stainless steel woven mesh or something like that will not blow out no matter what. This is probably the easiest to cut from a sheet to a shape that wraps easily around the sleeve. Then, outside that layer, I want a layer that fills the rest of the muffler case. For this outer layer, I want the maximum corrosion resistance and maximum sound absorption. Some kind of ceramic or rock wool packing might work well. There will be a small drain hole at the bottom of the end plate let the acid water leak out when the muffler cools. The weight is not a concern here, can be heavy (and maybe should be heavy to absorb sound better).

Question: Any specific materials and/or sources you've personally used and that can recommend?

Are you going to include a provision that allows packing replacement? I have not built double layered packed mufflers and perhaps the inner layer of SS wool will protect the ceramic packing from damage. I have read somewhere that ceramic and rock wool have superior sound damping qualities. All that said my experience with ceramic packing in motorcycle mufflers is it is woefully short lived. It gets shattered by the percussion of the exhaust and blown out. I prefer long strand fiberglass packed firmly.

[ptuomov]

A general question to people with muffler making experience:

I want a two-layer packing for the muffler. There will be a conical perforated sleeve that joins 2x3.5" to 1x4.5" tubes. This conical perforated sleeve will be surrounded by packing. I want the inner layer from high-temperature stainless steel woven mesh or something like that will not blow out no matter what. This is probably the easiest to cut from a sheet to a shape that wraps easily around the sleeve. Then, outside that layer, I want a layer that fills the rest of the muffler case. For this outer layer, I want the maximum corrosion resistance and maximum sound absorption. Some kind of ceramic or rock wool packing might work well. There will be a small drain hole at the bottom of the end plate let the acid water leak out when the muffler cools. The weight is not a concern here, can be heavy (and maybe should be heavy to absorb sound better).

Question: Any specific materials and/or sources you've personally used and that can recommend?

Are you going to include a provision that allows packing replacement? I have not built double layered packed mufflers and perhaps the inner layer of SS wool will protect the ceramic packing from damage. I have read somewhere that ceramic and rock wool have superior sound damping qualities. All that said my experience with ceramic packing in motorcycle mufflers is it is woefully short lived. It gets shattered by the percussion of the exhaust and blown out. I prefer long strand fiberglass packed firmly.

I don't want to replace the packing. So how about inner steel mesh layer and outer fiberglass layer, with some steel mesh on the bottom for the acid water and the drain hole?

[pdq67]

Per D2k, my 496" BBC engine at 550hp/5500 rpm and 580T/4500 rpm.

Its basically just a, "tow-truck", engine..

pdq67

[ptuomov]

Per D2k, my 496" BBC engine at 550hp/5500 rpm and 580T/4500 rpm. Its basically just a, "tow-truck", engine. pdq67

I'm going to "play" with the caveat that I don't know anything about exhausts or Camaros or Camaro exhausts. Just basically having read some books and having stayed at the Holiday in one night...

I assume you currently have dual 2.5" pipes from front to rear, with at least one cross-over, and then two muffler on each side (makes four total). One muffler set is two 18" long mufflers and another set is 12" long mufflers, both "turbo" style mufflers. That's not silly, but you might want to experiment and try replacing the second pair of mufflers with a packed oval case muffler such as a pair of Magnaflow 11366s or something. You might like the sound better as that might take more of the high frequencies out -- it's a modern day glass pack. Who knows?

For more complete do over, I'd probably think about the following. How about 3" from the exhaust manifolds or headers into a large H or X pipe that fully combines the pulses. From there, I'd continue with dual 3" to large chambered muffler, say Magnaflow XL 13269 (https://www.magnaflow.com/products?partNumber=13269). I'm thinking that chambered muffler probably takes out some of the low frequencies, and your big cylidners probably produce a lot of those. After those mufflers, I'd maybe run 3" for a while but step down to 2.5" right before two packed oval mufflers, such as a pair of Magnaflow Straigth Thru 11366 (https://www.magnaflow.com/products?partNumber=11366). Then 2.5" tail pipes out.

It's worth repeating that I know _nothing_ about this car or engine or anything, so let me just speculate and others can then correct me or just laugh at me...