My 3" custom exhaust with spring loaded flapper valve
02-16-2012, 01:38 PM
#41
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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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02-16-2012, 05:48 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.
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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04-27-2012, 04:42 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") !
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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11-18-2012, 01:52 AM
#50
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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11-18-2012, 01:09 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
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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11-18-2012, 07:38 PM
#60
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.
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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