Subbed to this thread, i have this 3" MAG 13219 universal XL performance, center inlet offset outlet
I really wanted a quiet setup so i chose a baffled muffler and used a vibrant resonator that is installed where the cat would be, but the system still drons at 3700 rpm and it gets old on the hwy and now it rattles at 3k pretty bad.
So i am looking for a new muffler now
a) 18psi's muff anus pic above doesn't resemble your 3rd drawing... it looks like there's an expansion chamber. I can see what appears to be the ends of 2 perforated pipes
b) I couldn't find a description of it on Magnaflow's website
I'm somewhat at a loss here, I'm not sure what else I can do to try to convince you.
In the above drawing pretty much everything inside the rectangular muffler body is made of 3" perf tube, other than the dual one that has twin 2.5" tubes. The thing you keep referring to as an "expansion chamber" is a Y section made of 2 pieces of roughly stamped steel. Its not a perfect Y but it does split the 3" flow into the 2.5" tubes, then recombines them at the other end. At no point does it open into the body of the muffler.
I mean, I actually own that muffler. If I had it here I'd be happy to take more pics for you but its at a friends place up near SF at the moment.
In fact, it looks almost exactly like this thing inside the muffler:
Anyone have any idea how much horsepowers are lost with the 12578? My wife and I just took a trip to the Mitty in the Miata, Va. to Ga. We could'nt hear the radio, so we cut it off. The drone gave me a headache after a while. Would lie to fix that without loosing my horsee's.