There you have it folks. This is why I love this forum.

With similar intentions, I just made a turn down that I swapped out at the flange right behind the diff. Mine was a 3-bolt, but a v-band would be ideal. Turn downs work wonders for reducing measurable sound track side and the vband would allow "tuning" via direction. You could also include a bullet type muffler for more sound reduction.

It really sounds like the op needs the MONSTER magnaflow that half this site runs. Anyone got the part number?

Magnaflow 12589.

thank you guys for all the info!

About the backpressure: (take me as a noob, I began to learn about turbocharged engines this year)
I said that the situation that requires less back pressure is wot+low revs+no boost (yet) because if a backpressure is present, the difference between manifold pressure and downpipe pressure (the only thing that gives energy to the compressor wheel) drops, and the rpm boost threshold goes up. This backpressure also increases the turbo lag at all rpms.
So the dynomax VT muffler is not ideal for me, expecially because my manifold is made in stainless (quick heat transfer) and is long enough to lose quickly heat: heat drop across manifold==>less pressure. Same story: I need a straight-thru muffler...

Please, feel free to correct me if my english is incorrect, I prefer to not be misunderstood...

:makeout:

now I have a full list of what I need to build a 3" v-band straight-thru exhaust line :brain:

do you intend two mufflers in a row?
is this one what you are meaning? JEGS Performance Products 30292 JEGS Flowpack Bullet Mufflers - Free Shipping on All Orders @ JEGS

Not two- you just swap it out at the track (or at home) with a single vband connection as pictured.

Yes- but that one is probably too long. This: Dynomax 24249 Dynomax Race Bullet Mufflers - Free Shipping on All Orders @ JEGS

https://www.miataturbo.net/attachmen...ine=1415197155

My .02: turn downs are stupid loud. Like, unless you're deaf or love to wake the dead, I wouldn't run one. Bullet mufflers are not really good at "muffling" either, they just soften the raspiness. For a proper muffler you want lots of packing. For a proper muffler you want no bottlenecks. The Magnaflow we keep talking about does both of those things, which is why we love them so much. You get maximum sound redux with minimum backpressure. win/win. No need to really swap anything or do anything. Weld one on and never worry about it again.

^ This.

All this business of swapping mufflers is just added complexity for the sake of loudness. The Magnaflow mufflers referred to above (such as 12589) consist of a perforated straight tube surrounded by packing material. No baffles, no louvers. If you look into one end, it's like you're staring at Hustler's anus- just a big, gaping hole that you can see clear through to the other end of.

https://www.miataturbo.net/attachmen...ine=1415201761

Such a muffler is no more restrictive than a cherry-bomb / bullet style muffler, merely quieter.

but but but joe that extra 10 pounds positioned in a favorable place is going to have such a huge effect on my lap times.

In the interest of cheap- he could have what he wants (quiet daily, loud track) since he already has both the track/bullet muffler and the quiet street muffler. All for the cost of a flange. I would debate the bullet muffler and turn down dropping sound levels as I have used them successfully on countless race cars. Of course I wear ear protection on track and assume others would also. Of course my track cars have always been separate from my street cars- and my street car runs a giant magnaflow for all the reasons cited. And this was coming from a turbo muffler. But then there's this:

And that's not the first time I've read or seen this on boosted cars. Though I never got around to testing it myself, it was on my list. In the end my general feeling is that driver is always leaving more on the table than something nominal like a muffler change, even if it's not that much work. And if you're not competing what's the point?

If the muffler packing density becomes too low from the packing burning out (or just being poorly made) then yes that magnaflow can become a massive restriction.

magnaflow 12589 ordered, as v-band flanges, s13 downpipe, flex joint, spill free funnel and things.. many other things.

Today I've done a compression test: warm engine, new compression tester (gauge style), very low battery.

c1: 75 psi
c2: 74 psi
c3: 70 psi
c4: 72 psi

but... the car is running great, and standard values are around 135+
I don't get it... really!
bent rods?

Possible causes of low numbers on a compression test:

1- Battery not fully charged.
2- Throttle not open during test.
3- Low compression.

new test with a car running in parallel: 85-85-82-85
I'm running most of time on LPG with low boost and low revs, but I'm thinking about a little bit of valve leak.
(cranking was slow even with a second car)
Sure the compression is low, but 85 psi is toooo low...

You left out number two. Throttle must be held wide open.

I also left out #4, which was "Compression gauge inaccurate / malfunctioning."

Consistency between cylinders is the most important attribute when compression testing anyway.