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View Full Version : All About Exhaust Flex Pipes (Flex Bellows)



Fredoops
05-08-2013, 10:55 AM
Figured I pop this here so in the future people have something to reference to when trying to understand different types of flex pipes.

What do Flex Pipes do?
1. Reduction of the vibration generated by the engine (especially for vehicles with transverse mounted engines and turbo engines)
2. Noise reduction
3. Heat Isolation
4. Prevention of hardness in exhaust systems
5. Compensation of thermal expansion

All flex pipes have a braid cover outside, usually with stainless steel. However, there are 3 different types of flex pipes, based on the construction of the interior.

Non-Lined Flex Pipes
Used mostly on older cars, as the name suggests, theres no lining inside, which can cause extra "whistling noise" (ie: worse than the whistling noise you already get from some SS headers)

Braid Lined Flex Pipes
As name suggests, this type of flex pipes have an internal braid to cover the inside, this allows a lower noise level and a higher heat resistance, especially on engines with turbos.

Interlock-lined Flex Pipes
Those flex pipes have an interlock liner made from a stainless steel expandable hose instead of braid like above. This type of Flex pipe reduces noise level even further, and can tolerate even more movement in the exhaust system.

Hope this helps.

EDIT:
Source: http://www.forss.ee/public/files/Flex_Pipe_Catalogue.pdf

bennjamin
05-08-2013, 11:11 AM
Can you quote the source information please.

Fredoops
05-08-2013, 11:18 AM
done.

Chr1s
06-08-2013, 10:22 AM
Length of flex is something to consider too, usually shorter ones don't last as long in certain applications (for obvious reasons)

ALLMTR996
06-08-2013, 04:17 PM
Length of flex is something to consider too, usually shorter ones don't last as long in certain applications (for obvious reasons)

And be very careful with the type of flex as the internal braided ones fail in something that has very hot exhaust gas like a turbo or E85 fueled car.

yabloko
09-08-2013, 11:59 PM
I've used a rather short one (~20cm overall) with interlock insides to join 4-2-1 stock d16a9 ex mani with the rest of the exhaust, exactly in the same place where stock graphite gasket is.
~20k km, no complains =)