I tried one of those.. on the way home from the muffler shop, I found a bit of the packing had blown out..
https://i.imgur.com/HZkRP9R.jpg?1
https://i.imgur.com/BIeRIpu.jpg

So I cut it open to find the join was like this:
http://i.imgur.com/ifwmiYf.jpg
https://i.imgur.com/Qaun2MS.jpg

These mufflers are designed to flow from one side to the other and not be mixed or merged from opposing sides.. save your money and learn from my mistake. I had it welded and repacked but it was still not a great performer.

Here is my video...from Feb 2019
<iframe width="560" height="315" src="https://www.youtube.com/embed/SffQ7vq9YLk" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

Just installed an M&K 1 in 1 out on the 86 911 last week, perfect fit, great quality, fantastic sound. Highly recommend.

I don't think the crossover design is inherently bad, but correct implementation is challenging on a 911. the crossover muffler is designed to have both inlets enter from the same end of the muffler, and both outlets would correspondingly be at the other end. in order for the X to work correctly the flow need to be in the same direction where the exhaust streams intersect. The H6 in the 911 leads to the most convenient configuration of having the two banks of the engine enter a muffler from opposite ends, which will cause flow issues with the crossover muffler design. If one were to route both banks to the same undo of the muffler it would probably work well.

One idea I've had the with Magnaflow arrange it so flow is in on the top two, and flow out on the bottom ports. Then weld in a divider plate in the top section of the X, this prevents back flow between the banks. Then also drill a few larger holes to allow some more of the exhaust pulses to diffuse out of the pipe, and pass through the resonance chamber, this should quiet it down some maybe.




http://forums.pelicanparts.com/uploa...1581053679.png

Hi Andy
I have also tried this muffler.
It worked "ok".. for stock motor I can see no downsides. The sound was deeper, and the quality of the muffler was excellent. For my motor, it felt a little lacking in power up top. William Knight predicted I would be leaving some hp on the table with this one, and the seat-of-the-pants dyno, agreed..I cannot remember if I had this one dynoed, but when I tuned it on the road using the logs for the AEM, I found my VE was approx 10% lower from 5k upwards...
Sound was nice though...

What muffler bracket are you using on the engine console? What straps are you using?

I am having a heck of a time getting the Dynomax 17231 muffler to mount nicely on the early 70's muffler bracket.

My 17231 gave up the ghost this week.

It started as a rattle noise that got worse and worse. I've thrown the BBE muffler back on for now. Can hear myself think again but I'm missing the power so I'm gonna take this one back to Advance Auto and exchange it for another. It has a lifetime warranty after all!

http://forums.pelicanparts.com/uploa...1583806691.jpg

Very interesting!
I remember on mine, I was getting what I called a 'resonance' at 2500 rpm.. I wonder if you had something similar which resulted in the muffler walls "oil canning" and flexing which eventually resulted in the crack?

Hmm I have the drone at 2200-2700 om my 3.6 as well. Did'nt you re-pack yours Mike?

Martin, I still don't know why my motor produced the resonance. I don't call it drone in my case. It was a strange resonance which would usually only be felt on the over run, ie a closed throttle. As the rpm would fall as I was coasting, it would start to create the resonance and in turn vibration, at about 2500 and by 1800 it was smooth again. Really strange... I don't know if it was the muffler, my tune, the 2.25inch piping, god knows what! What I found was that any muffler I used, which had the left and right exhaust banks crossing each other, would produced the resonance.
Any muffler combination which had separate banks, and no crossover, was smooth as silk.

So yes, my 17231 did get repacked, and initially when I ran it after repacking with more glass than was in there originally (maybe too tight?) the resonance and vibration was shocking! After it bedded in a bit, it did get smoother but there is still some vibration.
If I was driving and a cruise above 3000, no issue whatsoever and no drone.
Weird huh??

fyi, I also have a GT3 muffler I've been playing with.. if I use just the quiet ports, I get the same resonance and a little vibration through the car.
If I use the loud ports, it's pretty smooth.

If you look inside a GT3 muffler, the 2 quiet ports are pretty much firing straight at each other..

1987 cab with a 3.2 up'd to 3.5, twin plugged, 9.5:1, with 8-10 psi super charged boost on top.

Dansk SSi' with 2.5" secondaries into Dansk 2 in 2 out.
Felt the SSi secondaries were choking things up a bit as well
as the muffler's inlets.
Cut off the SSI's secondary after the merge collector.
Welded on a 2.5" flare.
Cut off the mufflers inlets, opened up the holes and welded in 2.5"
So it's 2.5" from the collector all the way into the Dansk 2 in 2 out.
Looks like the Dansk muffler uses 2.5" inside between its baffles.

Added V band clamps between the muffler and the SSi's so in the summer
we easily bolt on the 1.75" RSR headers.

So, we got plenty of breathing, sound notes are good and acceptable in a cab.

And, yes, that is a stock 3.2 oil line above the SSI.

http://forums.pelicanparts.com/uploa...1583857857.jpg

I tried to use this Dynomax muffler many years ago on my SC track car. Had the came problem with the center cracking. After the same happened with the second muffler I decided it was getting too hot and gave up on it. I had the proper set up with onside running thru top and other running thru bottom. I dynoed many mufflers compared to megaphones and a early two in muffler with outlets out the end was almost identical to magaphones. Hard to beat modified stock muffler except for the weight.

john

Here is what my setup ended up looking like:

http://forums.pelicanparts.com/uploa...1584070433.jpg
http://forums.pelicanparts.com/uploa...1584070433.jpg
http://forums.pelicanparts.com/uploa...1584070433.jpg

I don't have the bodywork back from the painter so the muffler exits have yet to be done.

Why are the rear tires so small? :D

#steamrollers

Winders - is that setup expected to pass sound at Laguna?

Actually, those ARE smaller tires than I normally run. The tires in the photo are only 12.4" wide. My normal tires are 13.6" wide!!

103dB sound, Yes. I am actually more worried about induction noise.