My 3" custom exhaust with spring loaded flapper valve - Page 3 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 02-16-2012, 02:38 PM   #41
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Quote:
Originally Posted by Efini~FC3S View Post
Honestly, I wish somebody would run with this idea but do a better job engineering it.
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.
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Old 02-16-2012, 03:19 PM   #42
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/\ DO IT!! omg do it and post vids

No but seriously, If you make 1 just make 2. And PM me your paypal address
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Old 02-16-2012, 03:56 PM   #43
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Originally Posted by Midtenn View Post
Then you wouldn't have to buy their muffler...
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.
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Old 02-16-2012, 06:48 PM   #44
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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.



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.
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My 3&quot; custom exhaust with spring loaded flapper valve-flapper-spoolup-comparo-blue-open.gif  
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Old 02-16-2012, 06:49 PM   #45
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Quote:
Originally Posted by 18psi View Post
/\ DO IT!! omg do it and post vids

No but seriously, If you make 1 just make 2. And PM me your paypal address
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...
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Old 04-27-2012, 05:42 PM   #46
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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") !

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My 3&quot; custom exhaust with spring loaded flapper valve-exh-backpressure-flapper-5-psi.gif  
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Old 04-27-2012, 09:00 PM   #47
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Here's the whole data set. Measured at downpipe.

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My 3&quot; custom exhaust with spring loaded flapper valve-exh-backpressure.gif  
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Old 04-28-2012, 01:45 AM   #48
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So how did my props go from like >10 to -2?
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Old 04-28-2012, 01:49 AM   #49
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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
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Old 11-18-2012, 02:52 AM   #50
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Originally Posted by JasonC SBB View Post
EVOs, F430s, and E46 BMW afaik have them.

EVO muffler cutaway: Flapper is in the upper left. The arrows show the flow while flapper is closed. When it opens it bypasses the circuitous route.

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
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Old 11-18-2012, 12:09 PM   #51
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I was gonna do it until I decided to go 3" + flapper.
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Old 11-18-2012, 02:01 PM   #52
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What gen Evo have those?
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Old 11-18-2012, 02:09 PM   #53
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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
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Old 11-18-2012, 02:10 PM   #54
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BTW I still have the EVO muffler in my attic, I can sell it.
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Old 11-18-2012, 07:16 PM   #55
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Corevette c6 does something similar with electric cutouts. Purrs like a kitten during normal driving... Floor it and the beast comes out...
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Old 11-18-2012, 08:05 PM   #56
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Yeah, I already made a thread about that lol.

In the end it just isn't worth the hassle on our cars.
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Old 11-18-2012, 08:14 PM   #57
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Quote:
Originally Posted by Stealth97 View Post
Corevette c6 does something similar with electric cutouts. Purrs like a kitten during normal driving... Floor it and the beast comes out...
Use a wastegate.
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Old 11-18-2012, 08:33 PM   #58
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Quote:
Originally Posted by triple88a View Post
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?)?
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Old 11-18-2012, 08:35 PM   #59
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Originally Posted by skidude View Post
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.
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Old 11-18-2012, 08:38 PM   #60
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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.
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