Graphite impregnated bronze bitches!

The spring tension is wrong. I will finger ---- a VT at the keystone bigshow March 3 to get a better feel for the tension then modify. This is for my subaru.

/\ DO IT!! omg do it and post vids:giggle:

No but seriously, If you make 1 just make 2. And PM me your paypal address:D

I highly doubt its more profitable for them to make the whole muffler and sell for 100 when they can make 20% of it and sell for 50-60. Just sayin.

I haz spoolup data

Flapper wired open, vs. normal spring loading.
3rd gear (6 speed, 3.9 diff), starting from 2000 RPM.
Note that I tie-wrapped it open, and did 3 pulls, then cut the tie-wrap, then did 3 more pulls. Cool morning, on a road 3 miles from home. As I did this, the oil was warming up. I have noticed before that as the oil and engine warmup, spoolup gets slightly slower, with no changes. So the test is biased against the later (hotter), spring-loaded test.

Blue is flapper open, Red is flapper spring loaded.

The difference is only noticeable above 3400 RPM and >~60 kPa. The difference is < 5 kPa and <50 RPM. In terms of time, the difference is < 50 ms! Note, the difference could be attributed to engine/manifold/turbo/oil temperature. I would have to repeat the test in the opposite order, but given how small the difference is, I'm satisfied that even if this difference were true, I'm happy with the results.

https://www.miataturbo.net/attachmen...1&d=1329432442

The low RPM portion does NOT show the red being better. That is a 1-2 shift.

When I drove with it wired open, the exhaust note was noticeably thrummier in around-town driving.

Actually if you make 1, just make 3. Seriously. PM me your paypal. I will be happy to pay for one that is modded to work well on a 2.5 suby...

I datalogged exhaust backpressure at the downpipe.
First half of the datalog was with the flapper wired open.
Then I pulled over and cut the wire and drove around some more.

After playing with the data the difference is clearest with the boost set to 5 psi (wastegate can pressure).

Plot below has RPM as the X axis and backpressure as the Y axis. It shows 2 distinct trendlines. The maximum difference is around 0.2 psi - much less than I thought! They converge at around 4000 RPM at 5 psi, which suggests this is where the flapper opens. Obviously at 15 psi it will open at a lower RPM.

And this is with the stiffer-spring option from Dynomax ("for > 400 hp") !

https://www.miataturbo.net/attachmen...1&d=1335559185

Here's the whole data set. Measured at downpipe.

https://www.miataturbo.net/attachmen...1&d=1335571192

So how did my props go from like >10 to -2?

Jason, love your constant datalogs.
But
You have yet to post up some good vides/sound clips of the comparison. Or maybe I'm just blind and don't see them in which case kindly point me to them.

*edit: no idea why you have negative props but I think I just "fixed" it:D

Bumping this because I've been thinking about this all day today, and have this idea:

WHAT ABOUT fitting a stock Evo muffler (like pictured) onto a 2.5" exhaust equipped miata?

Looks like it would more or less fit.

I text a friend who has one, and will go measure it tomorrow and see how crazy this idea might be.

I know on an evo they sound AMAZING. Seriously. When that little flapper opens up at WOT/full boost the car sounds great.

I kinda want my girly little car to sound like that :party:

I was gonna do it until I decided to go 3" + flapper.

What gen Evo have those?

That's from an 8, AFAIK.

BTW this blog post seems to indicate the 10 also has the same thing:
» EVO X/RalliArt – Inside the Stock Muffler Road /// Race Engineering

BTW I still have the EVO muffler in my attic, I can sell it.

Corevette c6 does something similar with electric cutouts. Purrs like a kitten during normal driving... Floor it and the beast comes out...

Yeah, I already made a thread about that lol.

In the end it just isn't worth the hassle on our cars.

Use a wastegate.

People have so much trouble with the electric cutouts and stuff because of the temperature. Why don't people just use a second wastegate at a different pressure? Or an electronic wastegate (do they have those?)?

Regular wastegate would be much cheaper, get a 3 or 6psi or whatever wastegate and call it done.

Because the biggest wg is still only 60mm.
And the "outlet" or whateve is still only like 38mm.
I've explored that option:

https://www.miataturbo.net/diy-turbo...winning-63536/

But gave up on it.

Of course you can always try the boost cutout things, but most (if not all) people admit they will not always seal properly. Just like electric cutouts. Unless there is constant tension on the little flapper/door via a spring, it won't seal properly.

Anywho, I'm still open to the idea, but kinda put it on the backburner.