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3" flexpipe for downpipe

v8volvoman1

v8volvoman1

Member
Joined
Dec 2, 2004
Location
06035
I was wondering what folks have been running for a weld-in flex pipe on their turbo Volvo. I bought a cheap 2.5" diameter flex pipe about three months ago and it has already blown out. Tell me what has worked for you (diameter, brand, mileage since exhaust was built, etc.), how long you've been running with it and what hasn't worked for you.

I need something more robust that's a weld-in application. I have a 3" downpipe reducing into a 2.5" and would like to extend the 3" a little further.
 
using a cheap-ish (35 euro) 3" flexpipe right behind the catalytic converter. Has been in use for 5 years now without issues. Only a bit rusty now. The damage is from some scrape on traffic bumps.
 
Try mandrel bend solutions. You want a flex coupler with a rigid interlocking liner. The cheap braided inner / outer develop a significant restriction over time as the inner braiding will swell inwards. Anyone who believes otherwise is fooling themselves.



Just used one of their 3" on my DP - I cut the external later of woven braiding off due to interference fit with my firewall
 
The flex pipes I use for builds are lined...they look like the cheap ones, but won't blow out. Make sure to check - they look the same.

10527595_10203357036501224_1554934037173626811_n.jpg
 
lummert said:
Why would a flex pipe be needed on a RWD car? I can understand why one would be needed on a FWD car.
Click to expand...

As you can see in the pic above the down pipe is secured to the engine, that leaves the rest of the exhaust going out the rear of the car (lots of weight) only supported with a few rubber hangers that are going to bounce around a little.

They may not be needed but it's cheap insurance to avoid cracking a manifold.
 
Having sold the big boy versions of these for marine and industrial diesels for about ten years, I've learned a few things.

First, you want to make sure it's an actual bellows, not just metal flex hose; bellows will take axial as well as lateral movement. Second, it's just meant to take up vibration and movement, not misalignment. And it can only move so far. Third, torsional stress will kill these quick - and it will split lengthwise like a zipper. If in doubt, two bellows at 90 degrees to each other will have near universal movement.

Oh, and that braid on the outside? When properly engineered, it helps damp out vibrations. Totally unnecessary for holding exhaust pressure.
 
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