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Old 02-02-2018, 05:21 AM   #15
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My understanding is the crimps are there as a deformable structure to protect upstream exhaust and engine in the case of a rear end collision. Power losses? I have no idea and not worried about it.
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Old 02-02-2018, 07:25 AM   #16
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Quote:
Originally Posted by BurningMan View Post
My understanding is the crimps are there as a deformable structure to protect upstream exhaust and engine in the case of a rear end collision. Power losses? I have no idea and not worried about it.
I've seen that theory posted several times, but I'm very skeptical of that one. If that were true I think we'd see similar crimps on all production exhaust systems.

Also, it does look like the exhaust may need to route around some bracing on the convertible models. I suppose the exhaust could have been designed first and the bracing just took advantage of the space, but that seems unlikely. GM simply using a single part that would work for both the coupe and convertible models seems very reasonable.

Maybe after some of the other burning questions get answered, we can get an official answer from Al.
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Old 02-02-2018, 11:45 AM   #17
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Originally Posted by parish8 View Post
here is what holly is claiming with their crush pipe delete kit.

I would expect the crimped section to have a significantly higher impact on performance at high flow conditions compared to low flow conditions. The dyno chart shows a similar delta at low speeds (lower flow) and high speeds (higher flow). Whatever caused that delta was likely not the crimped sections.

Mishimoto already ran a back to back test showing transparency between the crimp and full tube in that section of the exhaust:

https://www.mishimoto.com/engineerin...he-crimp-myth/


The crimp definitely reduces cross sectional area (significantly), but is so far downstream from the combustion chamber that the exhaust gas has cooled substantially and does not cause much impact on the torque curve of an otherwise stock car. As HP levels (and exhaust flow) increase, I'd expect that could be a bigger factor. For similar reasons, the stock SS exhaust produces about the same torque/power curve as the optional NPP exhaust.
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Old 02-02-2018, 12:00 PM   #18
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It'd be great if we could simply find someone with a ZL1 convertible that'd be willing to take a few photo's of their chassis where the exhaust crimps are to confirm positively that the crimped portion does indeed coincide with the vert chassis bracing.
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Old 02-02-2018, 03:43 PM   #19
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2lt has same crimps,I think it's a ground clearance issue as well as suspension clearances
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Old 02-02-2018, 06:47 PM   #20
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I have a 2ss vert and have seen these crimps. Didn’t pay to much attention. I’ll crawl under ther in the morning and get some pics. I have the braces unber there also but can’t remember exactly how it all lines up. Will update in the am.
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Old 02-02-2018, 07:14 PM   #21
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Quote:
Originally Posted by parish8 View Post
here is what holly is claiming with their crush pipe delete kit.

The company selling the delete kit....
...ya. I can see how their test is objective and not bias.
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Old 02-02-2018, 08:48 PM   #22
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So is the 3% change in CF the reason the blue line is 3% higher?
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Old 02-02-2018, 08:58 PM   #23
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Quote:
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So is the 3% change in CF the reason the blue line is 3% higher?
That's not really how it's supposed to work, but I had a similar thought when I first saw the chart.
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Old 02-02-2018, 09:28 PM   #24
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That's not really how it's supposed to work, but I had a similar thought when I first saw the chart.
Yeh I know it’s to compensate back to “STP”... it just looks bad. 6 months between runs is a while. I’d rather see a same day test.

Then I’d ask why there was low end torque improvement when a flow restriction should really only benefit the top end when the engine is at max gas output. The whole thing smells a bit off to me.
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Old 02-02-2018, 09:44 PM   #25
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Quote:
Originally Posted by Gunkk View Post
Yeh I know it’s to compensate back to “STP”... it just looks bad. 6 months between runs is a while. I’d rather see a same day test.

Then I’d ask why there was low end torque improvement when a flow restriction should really only benefit the top end when the engine is at max gas output. The whole thing smells a bit off to me.
The same day test is here: https://www.mishimoto.com/engineerin...he-crimp-myth/

That data makes more sense to me.
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Old 02-02-2018, 09:47 PM   #26
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Quote:
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At one time there was an issue with some aftermarket exhaust systems that touched the cross member and slight rattle caused the appearance of knock which would retard timing and pull power.
Not something you want to deal with.

Crimps have definitely been shown as a non-issue as far as power is concerned.


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...

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Old 02-02-2018, 09:49 PM   #27
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Quote:
Originally Posted by vtirocz View Post
The same day test is here: https://www.mishimoto.com/engineerin...he-crimp-myth/

That data makes more sense to me.
Nice find. Thanks for posting.
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Old 02-03-2018, 11:31 AM   #28
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With this dead horse, hopefully this will put this to bed.
We (the company I work for) build the exhaust for our cars, we (along with GM) develop this exhaust to perform a specific way. With out revealing details, I can assure you the crimped section DOES NOT lose or gain HP in any way shape or form. Doe it have a hindrance on sound? maybe to a slight degree that you would have to have the best ears possible to even identify it. Prior to the release of our cars, it has been tested for probably 18 months before its reveal. I hope this clears it up.
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