Help me design a muffler for 3.6 varioram

[Duc Hunter]

Ironically I have been taking to them as well. As JMZ says they only make a dual-inlet/Dual-outlet muffler in their X-pipe style. Since Bill V is of the opinion thats not good for our motors......that kind of sucks. "Progress." I hate it when companies take a perfectly good product, and change it for the sake of changing it. Probably did it as they use those resonators, and those X-pipes on lots of different exhausts, so it streamlines production speed and reduced costs. I do love my Fabspeed RSR system on my 3.2, that I put on it in 2015.

They want just under $2,000 for that setup, and they the told me it's only "slightly louder than the old suitcase style muffler."

Muffler looks like this one. This picture has cats up top and resonators on the bottom of the X I believe. A non-cat system would have resonators top and bottom. To my eye, and for my purposes (less noise), it seems like they could have a lot longer resonators, especially on the bottom....for the 964 and 3.2 style outlets. That would make the exhaust more quiet for sure.


They also said the 3.0, 3.2, and 3.6 RSR suitcase mufflers were all the same size and same size inlet and outlet pipes. Interesting.

[David]

I see this Fabspeed setup. Jay, did you ask what the header center to center dimension is on this?

With modified inlet and outlet pipes, this might work.

[targa72e]

I have made a couple mufflers using products from Cone engineering.

https://www.coneeng.com/index.html

I have a similar header set up on my 964 and built my own muffler. I used two of their 4" x 12" muffler bodies welded together and the end caps. Connection is via V-band clamps. I used their merge collector on the headers as well.

.




The inside of the muffler is a x design. All the straight sections internal to the mufflers were perforated tube. I used high temp packing made for off road motorcycle mufflers to stuff the case. drawing of internals.




The first one like this I made was for my 996 turbo. I used the 10" wide cases for it.



So you have a range of widths you can make the muffler and the tips.






I think they sound good and are not stupidly loud. They cost hundreds to make instead of thousands to buy.

john

[Duc Hunter]

Originally Posted by David

David, yes they still show that one (suitcase style) in the pictures. When you call though they say they dont make them any more and don't have any. They replaced it with a dual resonator type with a X.

[Bill Verburg]

Originally Posted by Duc Hunter

Ironically I have been taking to them as well. As JMZ says they only make a dual-inlet/Dual-outlet muffler in their X-pipe style. Since Bill V is of the opinion thats not good for our motors......that kind of sucks. "Progress." I hate it when companies take a perfectly good product, and change it for the sake of changing it. Probably did it as they use those resonators, and those X-pipes on lots of different exhausts, so it streamlines production speed and reduced costs. I do love my Fabspeed RSR system on my 3.2, that I put on it in 2015.

They want just under $2,000 for that setup, and they the told me it's only "slightly louder than the old suitcase style muffler."

Muffler looks like this one. This picture has cats up top and resonators on the bottom of the X I believe. A non-cat system would have resonators top and bottom. To my eye, and for my purposes (less noise), it seems like they could have a lot longer resonators, especially on the bottom....for the 964 and 3.2 style outlets. That would make the exhaust more quiet for sure.


They also said the 3.0, 3.2, and 3.6 RSR suitcase mufflers were all the same size and same size inlet and outlet pipes. Interesting.

It's not necessarily bad, just that many of the specific designs are poorly done and that is bad

The Fabspeed X pictures is one of the better implementations. In a poorly made system the 2 sides crash head on into ech other, In the Fabspeed they are parallel to each other at the connection.

Think about the gas flow


When the sides are kept separate there is a nice partial vacuum between the pulses of gas


when all cylinders are joined the space & pressure between them is degraded so that they interfere w/ each other to a greater extent.



as long as there are 2 parallel flows this is alleviated, and the faster acoustic signals are better dispersed, this helps suppress the dB levels.

sound suppression is all about giving the gas room to expand and slow w/o impeding flow, the more room there is the better this aim can be accomplished.

another view of 911 6 flow patterns
general picture


993 specific


993RS close up

[David]

Final muffler setup just waiting on the welder to tack it all together.

[Rivet]

Looking forward to a sound report!

I have the older Fabspeed designed full RSR exhaust with the muffler Bill likes but I am on the search for more power (and to smooth out some resonance issues with my power curve) and to refine the tone closer to what my ear likes. One of the idea's I had was very similar to this one, converting the Fabspeed headers to true V bands and a twin straight through design.

Looks great so far!

[3rd_gear_Ted]

Originally Posted by David

Final muffler setup just waiting on the welder to tack it all together.

Tilt the top of the muffler toward car for a better tuck I would suggest
I put a thermal wrap on the inside of the bumper to keep temp down.
Initial bumper surface temp readings w/o wrap was around 160F after a spirited drive

[scarceller]

What does this muffler look like internally? I assume perforated pipe straight across from inlet to outlet? Keeping the 2 banks separate so the left side flows straight through as well as the right side? It's desirable to keep the banks separated in the even fired 911 engine, I'm sure Bill may have pointed this out already.

Originally Posted by David

Final muffler setup just waiting on the welder to tack it all together.

[David]

Originally Posted by scarceller

What does this muffler look like internally? I assume perforated pipe straight across from inlet to outlet? Keeping the 2 banks separate so the left side flows straight through as well as the right side? It's desirable to keep the banks separated in the even fired 911 engine, I'm sure Bill may have pointed this out already.

Each side is straight through so no X in the middle which is surprisingly difficult to find. So left and right bank are completely separate except of course where they share the muffler packing.

[David]

A another Stainless Bros muffler pic for the records:

[scarceller]

Few followup questions:
What does this setup sound like?
How loud is it and any drone?
Is this the muffler you used?
https://www.stainlessbros.com/25-dualdual-ss304-dual-thin-oval-muffler-17-oal--polished.html
Also says the muffler is packed with fiberglass packing.

I'm looking to design a straight through setup like this and can't decided if I use single muffler like this one or 2 completely separate independent mufflers like 2 of these.
https://www.flowmastermufflers.com/products/exhaust/mufflers/laminar_flow_mufflers/super_hp-2_series/parts/12418409

The 911 engine is an even fired engine and does not benefit from mixing exhaust flow between banks.

Originally Posted by David

Each side is straight through so no X in the middle which is surprisingly difficult to find. So left and right bank are completely separate except of course where they share the muffler packing.

[RarlyL8]

We've been building mufflers like this for years. Parallel flame tunes, one per bank, separated but in the same case. It's basically a bullet muffler for each bank but with better packaging.



Currently we package the same design in our standard round shell. This is the internal pathway of the M&K MKM26 dual out muffler.

[Rivet]

Originally Posted by David

A another Stainless Bros muffler pic for the records:

I am very curious on what the tone is on this one. That option has been on my radar but have not used it yet.

[mikedsilva]

Originally Posted by Rivet

I am very curious on what the tone is on this one. That option has been on my radar but have not used it yet.

I had very mixed experience using these oval mufflers with the 2 perforated tubes running parallel.
Even though they are not 'joined' I found that at certain rpm, there would be a resonance. The gas paths are still colliding as they travel in opposite directions and spill out through the perforations into the muffler body.

Since using two completely separate straight throughs (like what Rarly mentioned aboe) ive had no issues at all.

[scarceller]

Exactly my concern with using a single can with straight through design. The banks still mix slightly.

Seems like this mixing has undesirable effect on sound and resonance.

Not sure if completely separate mufflers will do better but I assume so. I plan to build a individual banks with 2 of these mufflers.
https://www.flowmastermufflers.com/products/exhaust/mufflers/laminar_flow_mufflers/super_hp-2_series/parts/12418409

The other concern is bigger is not always better, using 2.5" pipe after the headers I think is to large. I suspect the pipe and muffler needs to be 2" or 2.25" I think I'll be using 2.25" pipe and mufflers.

Originally Posted by mikedsilva

I had very mixed experience using these oval mufflers with the 2 perforated tubes running parallel.
Even though they are not 'joined' I found that at certain rpm, there would be a resonance. The gas paths are still colliding as they travel in opposite directions and spill out through the perforations into the muffler body.

Since using two completely separate straight throughs (like what Rarly mentioned aboe) ive had no issues at all.

[Bill Verburg]

Originally Posted by scarceller

Exactly my concern with using a single can with straight through design. The banks still mix slightly.

Seems like this mixing has undesirable effect on sound and resonance.

Not sure if completely separate mufflers will do better but I assume so. I plan to build a individual banks with 2 of these mufflers.
https://www.flowmastermufflers.com/products/exhaust/mufflers/laminar_flow_mufflers/super_hp-2_series/parts/12418409

The other concern is bigger is not always better, using 2.5" pipe after the headers I think is to large. I suspect the pipe and muffler needs to be 2" or 2.25" I think I'll be using 2.25" pipe and mufflers.

mixing the expanded gas is a very different situation from mixing the main flow gases

Here's an older design Fabspeed that has filters out all resonance and most high frequency noise, the flow mixes after it enters the expansion chamber and so has no effect on flow efficiency



the offensive resonance depends on load but will always be present @ ~2k w/ headers tuned for max efficiency @ ~6.5 - 7k, Just as there is a peak for max resonant assisted flow there is a peak for max destructive flow .

a Helmholtz chamber is very good at filtering a specific frequency, other tuning aids are using an extended in let to the expansion chamber

the only issue w/ the 2 parallel but counter flow muffler model is that there is no internal expansion chamber to tune w/

also the larger the case the more room for expansion and absorption.

if the sides were to be merged it should look like this




Dinan also uses a well thought out absorption/Helmholtz design





and the DAnsk sport



this burns design is also nice but loud

[mikedsilva]

Originally Posted by scarceller

The other concern is bigger is not always better, using 2.5" pipe after the headers I think is to large. I suspect the pipe and muffler needs to be 2" or 2.25" I think I'll be using 2.25" pipe and mufflers.

I'm only a tinkerer at home, so limited experience but I did try different size pipes after the collector.
On a high comp 3.0 with itbs and georges euro headers (by gt racing) I fitted a GT3 muffler.
At first I tried 2 inch pipes from the collector to just the 'quiet' ports on the muffler and blanked off the larger ports.
The torque down low was huge! It felt like a modern turbo car. Amazing! But felt a little breathless above 5000.

Then I tried 2.5 from the collector to the large ports on the muffler and blanked off the quiet ports. It was loud AF, and lost ALL torque down low but it went hard at the top end. No good for me as no fun down low.

Went with 2.25 inch pipes from the collector into the quiet port. Seemed to work well everywhere. Not quite as punchy down low but it was not hindered up top. Seemed a good compromise.
Again, this was on a 3.0 with itbs.

[jmz]

Jury is out on the sound. It sounds very different than any flat 6 I’ve owned.

[David]

Sound video: https://youtube.com/shorts/SIXqZBIhBSU?si=kh9YzA4gQvEOPdUk