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flexible exhaust joints; yes/no, what type?


tneker
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At Road America last fall we were convinced we were down on power and weirdly enough we thought the car exhaust was perhaps quieter.  Part of my off season to do list therefore included exhaust system inspection to make sure glass pack from our glass pack muffler hadn't extruded out into the exhaust tubing.

 

Instead, I found the internal layer of our flex joint separated and choked off the flow path.  WTF.  

 

While we have pretty rigid engine mounting arrangement, we still felt some flex tubing would be a good idea between header and tubing mounted to car.  Perhaps that is a mistake....

 

What are you all running?  

 

 

ex pic 2.jpg

ex pic 3.jpg

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I run a rotary so I had enough problem getting solid pieces of mile steel tubing to live and changed over to all stainless from header to tip.

 

On the other hand I have worked quite a bit with flex joint manufacturers on multistage turbo systems, which is at least as tough of an application as rotaries. The bellows is made out of many layers of thin material, by varying the thickness, number of layers, and especially the material the manufacturers can support most any temperature and pressure…for a cost. The main difference between a flex joint that fits between turbos in a multistage system and a regular exhaust system one is the material used for the bellows, they can keep upping the material to higher and higher grades of unobtainium as the temps and pressures go up. Unfortunately it is hard to know any of this information at the consumer level.

 

One of the things you can check out is some of the design features. The best designs don’t have braided steel on the inside, they have floating solid pieces which act as a heat shield for the bellows and smooth out the flow.

 

 

flex.thumb.png.b838b45d6eeb16ea0c713f1a788a9b30.png

 

The other thing that you can do is pay attention to the instillation and how the loads go through the flex joint. On multistage turbos we were allowing for stackup and thermal growth between rigid mounted turbos, mounted to the exhaust system you have all that plus engine movement. The flex joints work very well flexing axially getting longer or shorter, they also do well in bending. They are still OK with offset, but will fail very quickly with any twisting load. When you are laying out your system do everything possible to eliminate any torque loads that can get into the flex joint either from movement or thermal growth.

 

Edited by mhr650
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On 2/18/2018 at 2:44 PM, tneker said:

At Road America last fall we were convinced we were down on power and weirdly enough we thought the car exhaust was perhaps quieter.  Part of my off season to do list therefore included exhaust system inspection to make sure glass pack from our glass pack muffler hadn't extruded out into the exhaust tubing.

 

Instead, I found the internal layer of our flex joint separated and choked off the flow path.  WTF.  

 

While we have pretty rigid engine mounting arrangement, we still felt some flex tubing would be a good idea between header and tubing mounted to car.  Perhaps that is a mistake....

 

What are you all running?  

 

 

ex pic 2.jpg

ex pic 3.jpg

yup not a fan of those. I have seen them come apart before. Also glasspacks are cool, but do the same thing and can actually restrict flow. Just get a cheap welded muffler and roll.

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