I suspect it is minimal.

https://www.miataturbo.net/attachmen...ine=1433000925

This image is interesting. You can see where the inside edge of the perforated internal tube "disrupts" the flow into the side tubes. On my 1x579 muffler there was one end that looked like the above pic, and the other end was actually much better. It may just be manufacturing tolerance (or lack thereof) or simply luck of the draw. My muffler is oriented so that the "better" side is the "inlet" side. I'd like to think that'll help.

I considered getting in there with some sort of tool and cutting down those edges but its all stainless. It looked like it was going to be a bitch to do so I moved on to other things.

Not sure on the 12579, but the 12578 is minimal. I used to run one as a Laguna exhaust on Theseus (normally ran that car straight-piped, no mufflers/resonators). There was no significant difference in the power with or without the muffler, and it took ~13dB off the exhaust note.

More precisely, I meant there was no cutaway view nor a detailed description nor the text "dual flow" on Magnaflow's website, according to google.

Now I get it. The above 'Y' has a flat surface between the dual tubes which is visible in 18psi's actual muff pic. What threw me off was the 'V' transition between the dual tubes in EO2k's sketch.

While much better than a simple expansion chamber, the flat instead of a 'V' will introduce some turbulence. It would be interesting to measure the actual muffler pressure loss. I measured mine some time ago, (3" straight through), and it was on the order of 1 psi including the bends before and after the muff, when the whole system including cat and downpipe was dropping ~4.

:bigtu:

If I can figure out some way to measure and log it, I'll try to do so. I know Ian asked as well over in his build thread.

That was my concern in the muff thread too, and then brainesack berated me for it, and since I'm too lazy to test this sorta stuff I just kinda didn't care.

In theory the noise redux should be significant, no idea about turbulence because it's likely not as significant as the sweet sweet quietness :D

I would speculate that it might effect the very top end, but under 5k worth of flow its probably negligible.

Priorities for me are sound reduction, then flow. In that order.

Measuring is easy if you have holes in the right places. I have the bits to instrument it if you want to bring it up to San Jose sometime.

--Ian

Once its up and running we can definitely make that happen. I know we have the same MS3-Basic so adding that stuff should be easy, now that you've figure out how to do it of course ;)

Make sure to lube your probe before you stick it in his hole

I said the same thing about the stupid louvered resonator I had before which had a shocking amount of pressure loss. I don't assume "it's probably all right" anymore.

Well don't get me wrong, flow is still super important. If I didn't care about flow at all there would be a louvered resonator in there along with a chambered muffler. I see the 1x579 series as a very minor compromise in the flow vs sound debate. It was a minor compromise I was willing to make, and I'm glad to provide data once its up and running.

In fact, if someone is willing to loan us a 1x578 or 1x589 series muffler, or if I can convince Gesso to buy one for his project, we can splice it into my exhaust and do some legitimate "all things being equal" back-to-back testing with Cordus' sensor setup. That'll really give us solid data.

You might want to consider welding in O2 sensor bungs in strategic location while it's easy to get to. My FM exhaust is designed to be usable with a stock ECU, so it's got three or four bungs in it (2 before the cat, and one or two after as well). I have an O2 sensor plug that I drilled and tapped for 1/8 NPT, so I can put the copper tubing for the probe into that.

--Ian

I like this plan. I'll add some mild bungs to my shopping list, and maybe an additional stainless one for the downpipe.

Out of curiosity, where would you recommend putting them/where exactly are the ones located in your FM?

The FM exhaust has one in the down pipe right where you can see it through the driver's side wheel well, which is actually really convenient to get to. The one for the wideband is right before the cat, located on top. There's also one right after the cat (actually in the cat pipe itself), and I think there's one midway down the mid pipe (where the stock 49-state second O2 sensor goes).

http://www.codrus.com/miata/fm2r/fm-exhaust.jpg

Actually, now that I look at the photo, I'm not sure there *is* one in the midpipe after all. The downpipe ones are obvious in the photo, and the post-cat one is right under the exhaust hangar for the midpipe in the photo.

For pressure sensing between the cat and the muffler, I don't really think it matters all that much, the pressure should be pretty constant all the way along the pipe. If you're trying to measure turbine performance, I think it's better to have them right before and after the turbine itself.

--Ian

Pre-turbine is going to be a problem for me. There really is no convenient place to put on in my manifold, plus its coated, or I could drill and tap a hole in the EFRs turbine housing. I'm not sure I'm crazy about either TBH. Someplace in the downpipe is do-able as is before the first resonator. We'll figure something out. ;)

Any reports back on which is quietest and still good power/spool.
About to pull trigger

12578 or 12579 or 12589?

I want quietest without much power spool sacrifice ( That not to much to ask for right LOL)

yes

I ended up with the 12589 because my installer requested it. More room to make the bend past the differential.I am completely satisfied with the sound level though, we made another trip to MATG. No headache and still feels like I have my power.Nice roar when I get on it too.