Going back to KTL’s diagram in post #20 above, the fact that 911 folks are using these 17552 or 17553 mufflers with inlets at opposing ends versus the way the mufflers were designed with both inlets in the same side (on the left in Kevin’s diagram) I would think that the exhaust is not merging but actually colliding inside the muffler. The angles of the X is designed for both inlets from the left.

The 17231 shows in the manufacturers data as reversible so I plan to use the lower left and upper right as inlets resulting in a true straight through flow for each side of the engine, and the chamber of the muffler would then act as a crossover of sorts. Assuming my 98db with straight through single chamber Flowmasters gives me problems. As of now, none of my usual haunts- Autobahn, Blackhawk, Road America, Mid-Ohio, Gingerman- have any limits. PittRace in May, don’t think they have restrictions either. But if I venture back to Road Atlanta then I might need to amend my thinking.

I don't disagree.
However I could have almost sworn I read a post somewhere else on PP, written by one of the very well respected and experienced members, that these engines "need" the cross over. Maybe I dreamt it.

Yes, I do believe I have some sort of reversion happening, but would like to know if the 17231 muffler (twin straight through) had similar effect before I go spending more money.....
Above 3k, this thing is amazing.

I read & constantly see people say they put on this & that, 2 in 2 out, 1 in 1 out, name dropping makers left & right, but in the end no one has mentioned what size tubing might be the best to use on a 3.6 engine.

Can anyone give a hint on diameter tubing used on above mentioned mufflers?
What size piping do the mentioned mufflers have &/or what size would most likely be the best to use on a "stockish" 3.6?

This is a very important statement. On mufflers as in headers, one size does not fit all applications. Mufflers are a bit more forgiving than headers in this regard but as Mike is seeing first hand there is a limit. Unfortunately the model of M&K muffler Mike has is not optimal for his application. Modified engines have specific needs when it comes to both header and muffler design. We have a Motorsport line of mufflers that can be customized for these applications.
As for internal tubing, the early 2.2L-2.4L engines can use tubing as small as 2"OD in applications that are often less than 150hp. Bump this up to a 3.6L and 2.5" may be fine for a stock engine and 3" for modified. This however is just one aspect of function. Baffling, flow paths and chambers also influence performance. The muffler Mike has now on his engine will probably work very well if you can divert the flow at an rpm that matches the change in resonance he is seeing. A valve on one exit controlled by a hobs switch would do that.

How did it perform at lower rpms. Any weird reversion or scavenging issues? I would imagine not as the pipes are straight through, however it might still be possible since they share the same muffler body and the flows go in opposite directions, maybe?
I've ordered one of these and will give it a go over the next few weeks.

I cannot help you since my motor (and I started this thread) is a 3.0. My headers are from GT Racing (formerly George's Euro Headers) and size is 1 & 5/8ths.
The Dynomax 17552 muffler I used has 2.25inch inlets and I had the exhaust shop use 2.25inch tubing to fit up the muffler.

And that is why i asked :) It's a jungle figuring out the best size, baffling and so on. Flow is dependent on plenty of things, just as you slightly mention, & among other things bends & turns make a great deal on flow/restriction of flow.

If Mike is using 2.25" tubing from headers out I suppose 2,5" is my minimum on a stockish 3.6..
Flow has been improved from throttle body all the way down to the cylinders & port matched all the way, light weight flywheel, engine is blue printed/balanced, bigger injectors & 993 headers w/ the heat boxes stripped off. Finally I'm building a custom exhaust.
My headers seem slightly smaller in diameter, 39mm, compared to Mikes 1 5/8" = 41mm ( if I'm correct).
The thought is to make is as quiet as possible....in my dreams i suppose ;)

This is still help & appreciated in deed :) I have something to compare with & I follow your progress comparing the difference. Nice thread & thanks for the input.

Which flowmaster muffler?

There are several with increasing levels of baffles and chambers.

It sounds and looks like a flowmaster 10

When J.W. built our 3.5 using George's 1 5/8" headers, they tested a couple of different mufflers. They were all tested on the same day. At that time we were using a Flowmaster 2 in/2 out. Compared to the J.W. twin straight mufflers the Flowmaster was within 5 h.p. and similar torque between 5,000 - 7,000 rpm. They both came on and went off the power band around the same rpm.
I was looking for a different sound and look. I bought a bare can from M&K, used George's tapered pipes for the inlet, made my own baffling and did a twin center outlet. The surprise was mine had
more torque and more h.p. at 4,500 rpm than the other two. It also started loosing power at 7,200 rpm where the other two stayed on power to 7400-7500 rpm. It had a 92 decibel reading at Infenion at full throttle. While this setup was good for our motor, not so good for a high winding motor.
The point is, finding a muffler that matches your motors power band, and as a by product the sound you want.

MikeDisliva has a new prototype, we will see how it does on the dyne once the tune is adjusted on the injection. It is designed for smaller motors unlike the Dynomax Mike is testing against the cup muffler. I still look forward to seeing the Dynomax design tested against the cup muffler on the same headers, I have photos of the first one I built and tried if anyone needs diagrams or photos. my email is knightrace@mac.com William Knight

You are correct, Flowmaster 10 series. 325108.

I personally like the deep tone of Magnaflow mufflers.

Magnaflow and Dynomax's will change sound as they break in, being a packed muffler. Mine was almost stock quiet when cruising and at idle when it first went in. Now, not so much. Still like it, don't get me wrong, but its def not stock sounding at idle anymore. FlowMaster's wont change as they are baffled, not packed.

What happens to packed mufflers that cause the sound to change? Does the packing get blown out over time, so it gets louder?

Internals of the muffler
 

When I first drove the car, a bunch of packing blew out.. which made me think the crossover was not properly welded.. and that maybe, this was the issue for the rough patch between 2000 and 3000 rpm.


Just to be sure, I bolted the M&K muffler back on and the car ran smoothly.. so at least I can rule out an engine issue.

I cut off the back of the Dynomax 17552 muffler and you can see the images below. I removed the packing... Do you think the fact that the welding isn't continuous, could have caused an issue with flow and created a turbulence which has an effect between 2000 - 3000 rpm?
https://www.youtube.com/watch?v=Zcz2_dGqNNY&feature=youtu.be

No I think that muff was designed to have inlets on one side and outlets on the other and thus the exhaust pulsing in from both sides destroyed it

I’m not sure how people get that muffler to work on a 911. Has to be tremendous turbulence at the merge, definitely not the way the flow path was designed

http://forums.pelicanparts.com/uploa...1550437946.jpg