My 3" custom exhaust with spring loaded flapper valve - Page 6 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-24-2015, 01:58 PM   #101
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Why not?
I didn't get the spring flapper, but the manual valve, but now I'm curious why you think that. The mitsu evo and many others do this very successfully
There's a 3d map for it, it's not just open when exhaust flow is above a certain level. I don't remember the details. German manufacturers want cars that are quiet at cruise and light acceleration loads, slightly louder at idle (make a statement at a stoplight) and then louder and fast when you romp on it. The Evo is a boy-racer sedan, refinement is much less of a concern for the manufacturer.

The Germans have been engineering the sound of their engines for decades, the current "put in a speaker to make it sound right" approach is simply the latest step.

--Ian
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Old 09-24-2015, 02:03 PM   #102
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You're just dismissing the evo, and I think that's kinda silly.
All 3 of the US generations have this setup, and I can personally attest to them being effective, and IMHO their stock exhaust system actually sounds really good for what they're working with (a not-so-good sounding 4 cylinder).

I know "ze germanz" have been doing all sorts of stuff for decades, I also know that "ze germanz" have some of the most problematic and issue riddled cars out there. I also know ze germanz have a reputation for having a "5 year car". It's why most of their value plummets with years.

I'm not hating on ze germanz, if I was balling enough to just make it rain money every few years on a new car I'd probably drive one, I just don't like it when you dismiss something simply based on stereotype of the car make.

Do we know why vacuum operated flappers are superior to spring loaded aside from being able to control when it opens for sound enhancement?
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Old 09-24-2015, 02:04 PM   #103
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at least im not a dog-owning lesbian anymore.

i never even said anything negative about your flapper...i just made a comment about modern oe cars still having vacuum operated flappers on the exhaust.
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Old 09-24-2015, 02:06 PM   #104
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I aint even mad at either of you.
I like this discussion.
I always wanted a silent car that hauls the mail (I know, I know, get a Tesla LOL)
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Old 09-24-2015, 02:06 PM   #105
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id rock a tesla.
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Old 09-24-2015, 03:03 PM   #106
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I'm not hating on ze germanz, if I was balling enough to just make it rain money every few years on a new car I'd probably drive one, I just don't like it when you dismiss something simply based on stereotype of the car make.

Do we know why vacuum operated flappers are superior to spring loaded aside from being able to control when it opens for sound enhancement?
I'm not dismissing the spring flapper based on the Evo. It doesn't solve the problem "ze Germanz" are trying to solve, so they don't use it, but Mitsubishi is building a different kind of car for a different kind of customer under a different regulatory scheme, so they don't need to solve that problem.

You're not trying to solve that problem either, so I don't think it makes sense to try to put one on a Subaru or a Miata, the spring flapper should be fine. I brought up the vacuum flapper originally as a joke, not a serious suggestion.

I found the spring flapper on Jason's car sort of annoying because you can hear it rattle sometimes, mainly when slow accelerating away from a stop. I dunno if that's a problem inherent to the concept or just a problem with the design of the one he has, but none of the vacuum-flapper cars I've driven have done it.

--Ian
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Old 09-24-2015, 03:05 PM   #107
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I found the spring flapper on Jason's car sort of annoying because you can hear it rattle sometimes, mainly when slow accelerating away from a stop. I dunno if that's a problem inherent to the concept or just a problem with the design of the one he has, but none of the vacuum-flapper cars I've driven have done it.

--Ian
This, is definitely interesting.
I've heard it mentioned a few times, and kinda figured it would likely sometimes do that, and it sounds like the issue is legitimate. And the "solution" of going stiffer spring would likely build more backpressure, so that's no good.
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Old 09-26-2015, 11:29 PM   #108
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Stiffer spring would only build more backpressure up until the point it opens.
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Old 09-27-2015, 07:56 AM   #109
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You might not like the results with a spring flapper that operates on exhaust pressure. The pressure goes up, the valve opens, the pressure drops as a result, the valve closes, the pressure rises again, the valve opens again - you have just created an exhaust-powered clarinet with the valve acting as the reed. Without damping, it will oscillate because of the unstable opening force. Add exhaust pulses and the effect is like a clarinet with tremolo.
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Old 09-27-2015, 10:56 AM   #110
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^... which is prevented by designing the valve so it has a lot of hysteresis.
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Old 09-27-2015, 03:18 PM   #111
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Old 09-28-2015, 11:49 AM   #112
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Old 09-28-2015, 01:02 PM   #113
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what year is it??!
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Old 09-29-2015, 02:39 PM   #114
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Back to the future!
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