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Old 02-03-2018, 01:05 PM   #29
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Thanks for that confirmation. FYI: It looks like Faurecia makes the stock exhaust - at least that’s what’s stamped into the muffler. Whoever was in charge of the exhaust did a great job!
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Old 02-03-2018, 01:09 PM   #30
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The cross-sectional area of the pipe is virtually unaffected. This was a clever, albeit unconventional solution to an annoying problem. Don't let the look of it get under your skin and waste money that could be spent on a more effective mod. Mishimoto's test is good...this video helps shed some light, too...

Don't forget the header bash test..... very telling.

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Old 02-03-2018, 02:27 PM   #31
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Don't forget the header bash test..... very telling.

Geese, that's what I meant to post!!! Did I copy the wrong link?!?!
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Old 02-03-2018, 08:07 PM   #32
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Geese, that's what I meant to post!!! Did I copy the wrong link?!?!


I think it still applies, it's all back pressure.
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Old 02-05-2018, 10:28 AM   #33
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Originally Posted by vtirocz View Post
Thanks for that confirmation. FYI: It looks like Faurecia makes the stock exhaust - at least that’s what’s stamped into the muffler. Whoever was in charge of the exhaust did a great job!
were pretty proud of it.
we also make the GMT900, K2XX and the upcoming T1's. just a tipoff the iceberg on what we do.
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Old 02-05-2018, 03:29 PM   #34
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were pretty proud of it.
we also make the GMT900, K2XX and the upcoming T1's. just a tipoff the iceberg on what we do.
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Old 02-06-2018, 07:49 AM   #35
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Sorry, but your “theory” is 100% patently false. By your “theory” If there was 1” of exhaust length that was only 1mm diameter it would not effect performance much if at all because the length of the restriction is so short. That’s just not true.
DG is actually on the right track.

Flow restriction (and the attendant power/torque loss) is not just about the length of a reduced cross section area any more than it's only about what the cross section area was reduced to. And this only addresses the steady flow portion of the problem.

The amount of "backpressure" an undimpled pipe has is probably only a fraction of one psi over the entire length, maybe something like 0.2 psi (I did look at some low pressure gas flow charts for this). Suppose that length from converter to muffler is 5 feet, so that becomes 0.04 psi per foot. Now let's make the crimp such that its resistance becomes 0.2 psi per foot (a good bit more severe than the case here), making the total pipe backpressure about 0.04*4.5 + 0.2*0.5, or 0.28 psi. So you've added less than 0.1 psi of backpressure . . . and to give that some context, each whole psi of backpressure costs about 7% power but you're gaining less than a tenth of that (around half a percent).


Any change in cross section shape (even if the inside area remained the same) has the potential for affecting system resonances and their effect on tuning. This might even be a larger effect than the steady state part, at least within some rpm range or ranges.


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Old 02-06-2018, 11:16 AM   #36
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Originally Posted by Norm Peterson View Post
DG is actually on the right track.

Flow restriction (and the attendant power/torque loss) is not just about the length of a reduced cross section area any more than it's only about what the cross section area was reduced to. And this only addresses the steady flow portion of the problem.

The amount of "backpressure" an undimpled pipe has is probably only a fraction of one psi over the entire length, maybe something like 0.2 psi (I did look at some low pressure gas flow charts for this). Suppose that length from converter to muffler is 5 feet, so that becomes 0.04 psi per foot. Now let's make the crimp such that its resistance becomes 0.2 psi per foot (a good bit more severe than the case here), making the total pipe backpressure about 0.04*4.5 + 0.2*0.5, or 0.28 psi. So you've added less than 0.1 psi of backpressure . . . and to give that some context, each whole psi of backpressure costs about 7% power but you're gaining less than a tenth of that (around half a percent).


Any change in cross section shape (even if the inside area remained the same) has the potential for affecting system resonances and their effect on tuning. This might even be a larger effect than the steady state part, at least within some rpm range or ranges.


Norm
I wasn’t off track. My simple argument was that cross sectional diameter is absolutely a factor in flow, even if for a relitivly short amount of length. If 1” of a ZL1 exhaust is only 1mm in diameter.....it will equate to a massive change in exhaust pressure. That’s all I was saying. It can’t be “written off” because it’s only 1” long. That was the vibe I got from the previous post.
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Old 02-06-2018, 05:06 PM   #37
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Crimping provides about an 1" of clearance from 'vert cross brace on my ZL1.
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Old 02-06-2018, 05:10 PM   #38
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Crimping provides about an 1" of clearance from 'vert cross brace on my ZL1.
This pretty much confirms Chris V's post, and answers my question.

Thanks for the pictures!
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Old 02-06-2018, 06:10 PM   #39
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Excellent info!! Thanks!
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Old 02-06-2018, 06:37 PM   #40
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Originally Posted by ninetres View Post
IIt can’t be “written off” because it’s only 1” long.
No, not entirely.

But DG's theory, which you specifically called 100% patently false, is absolutely on the right track, as it did consider both cross sectional areas and lengths.

Quote:
Originally Posted by ninetres View Post
Sorry, but your “theory” is 100% patently false.

I know that it's possible to construct outlandish examples that appear to prove something to be generally true when that is absolutely not the case, and that's when the sanity check requires actually running a few realistic numbers and letting the answer fall wherever it may instead of trying to hand-wave the whole thing away by implying that a simple comparison to the absurd is sufficient.

I'm not trying to say that 1" of 1mm tubing wouldn't restrict flow severely (it'd probably choke the flow off to some smallish fixed value no matter how much pressure you put behind it, and how much power that would cost). But I will state that 1" of 1mm doesn't represent what's going on in the pinched sections of Camaro exhaust tubing well enough to have any meaning at all.


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Old 02-06-2018, 09:49 PM   #41
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Originally Posted by Norm Peterson View Post
No, not entirely.

But DG's theory, which you specifically called 100% patently false, is absolutely on the right track, as it did consider both cross sectional areas and lengths.




I know that it's possible to construct outlandish examples that appear to prove something to be generally true when that is absolutely not the case, and that's when the sanity check requires actually running a few realistic numbers and letting the answer fall wherever it may instead of trying to hand-wave the whole thing away by implying that a simple comparison to the absurd is sufficient.

I'm not trying to say that 1" of 1mm tubing wouldn't restrict flow severely (it'd probably choke the flow off to some smallish fixed value no matter how much pressure you put behind it, and how much power that would cost). But I will state that 1" of 1mm doesn't represent what's going on in the pinched sections of Camaro exhaust tubing well enough to have any meaning at all.


Norm
What I meant (and obviously wasn’t clear enough) was that it’s absolutely 100% patently false to disregard cross sectional diameter if it isn’t of substantial length. Diameter effects exhaust flow/pressure at any length. As you said, it’s part of a mathematical equation. It isn’t magically “removed” from the result if the length is under X amount of length.

My take-away from the original post we are hashing our was that the flow is not effected if the “restriction” doesn’t reach a certain length. It does. Regardless of length, there will be an effect.
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Old 02-07-2018, 07:29 AM   #42
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What I meant (and obviously wasn’t clear enough) was that it’s absolutely 100% patently false to disregard cross sectional diameter if it isn’t of substantial length. Diameter effects exhaust flow/pressure at any length. As you said, it’s part of a mathematical equation. It isn’t magically “removed” from the result if the length is under X amount of length.

My take-away from the original post we are hashing our was that the flow is not effected if the “restriction” doesn’t reach a certain length. It does. Regardless of length, there will be an effect.
Agreed, and it appears that we might have been looking at the way the original post was phrased a little differently.**

What's left once we see that crimped region (and what actually matters) is whether or not the effects from it are significant. Seems a lot of people think it does simply because it looks like it should, and these people generally lack the analytical tools to either justify or debunk it on their own. Not that others being ready and willing to take advantage of that belief by pitching it in their advertising is helping.



** I used to review technical documents prior to issue as part of my day job, so maybe I still basically see things differently from most even though I'm over 5 years retired.


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