Cracked Bellows

[Chris Huggins]

Any advice on downpipe/exhaust fabircation in relation to thermal expansion compensation?

 

Old down pipe on the right.  new downpipe on the left.

 

The old one has survived 100+ hours of abuse with no thermal compoensation.

 

The new one failed with less than 2 hours on it at the bellows.  The bellows was a "good idea" that bit me in the tail, right?  I'm planning on just welding it back with solid tube and sending it.  

 

Any other gotcha's that i'm missing here?

 

 

Edited July 29, 2021 by Chris Huggins

[Team Infiniti]

12 minutes ago, Chris Huggins said:

missing

Link no work on phone or lappy.

 

[jakks]

We have to weld in a bellows about every year on RBR. 

[enginerd]

The only problem I see is that it isn't one of these:

https://vibrantperformance.com/catalog/index.php?cPath=1527_1064_1114&osCsid=e707c55c137839143d4ce97fa6600ea1

[MichaelPal]

After the v-flange at the manifolds, how far is your first hard clamping point? 

Old vs. new? 

[Black Magic]

Do you need the bellows? Looks like you have room for thermal expansion at the Y, if  you make slip joints there. If you have welded the pipe at that point, hopefully you can remove the weld. At the slip joint use tabs and bolts with mechanical interference nuts to keep the slip joint from separating. Design the joint so the slip joint is only 3/4 or so engaged when at rest (room to grow) with bolts set to have minimal slop at this point.  

 

FWIW most of the race cars I have seen use slip joints over bellows. On my own cars I have never been able to make the bellows last when mounted near the engine\hot side of the exhaust. 

Edited July 29, 2021 by Black Magic

[Chris Huggins]

41 minutes ago, Black Magic said:

Do you need the bellows? Looks like you have room for thermal expansion at the Y, if  you make slip joints there. If you have welded the pipe at that point, hopefully you can remove the weld. At the slip joint use tabs and bolts with mechanical interference nuts to keep the slip joint from separating. Design the joint so the slip joint is only 3/4 or so engaged when at rest (room to grow) with bolts set to have minimal slop at this point.  

 

FWIW most of the race cars I have seen use slip joints over bellows. On my own cars I have never been able to make the bellows last when mounted near the engine\hot side of the exhaust. 

These?

 

How do those give any expansion room?

[MichaelPal]

Those don’t. The slip does. Those are the wrong axis  you want threads along the flow of Exhaust. To provide the mechanical “maximum expansion point” 

 

slip = this. I use springs instead of mechanical threads/fasteners. 

Edited July 29, 2021 by MichaelPal

[Bill Strong]

1 hour ago, enginerd said:

The only problem I see is that it isn't one of these:

https://vibrantperformance.com/catalog/index.php?cPath=1527_1064_1114&osCsid=e707c55c137839143d4ce97fa6600ea1

 

 

That's what I use and have over 6 years on it.

[Bill Strong]

Going from 3 bolt flange which gives some wiggle room vs,. the solid un-moving V-band is your issue.

 

[Chris Huggins]

So these, at the slip where the runners enter the merge?

Edited July 29, 2021 by Chris Huggins

[enginerd]

Our M20 exhaust setup. One vibrant flex where the stock bellows is and another after the merge.

[Chris Huggins]

24 minutes ago, enginerd said:

Our M20 exhaust setup. One vibrant flex where the stock bellows is and another after the merge.

 Yep, that looks like my M20 exhaust.  I used the other Vibrant Bellows.  I think because of the increased angle the thermal expansion was correct in the M20 use case and it has survived a long time.

 

In the M54 use case the angle is different because both manifolds are rear exit and the thermal expansion put side-loading on it instead of linear growth.

 

https://vibrantperformance.com/catalog/index.php?cPath=1527_1064_1254

[mhr650]

I can add one extra point, I have worked with bellows engineers on multistage turbo applications. The one thing that will always cause bellows failure very quickly is any twisting motion. In your case since you also replaced the 3 bolt flanges with v-bands it could be possible that once the connections were up to temperature the v-band flanges slipped and caused a twisting load to the bellows. Its also possible that in the instillation process the flange had some twisting motion as the v-band was tightened down.

 

I would always prefer a v-band flange over a bolted flange, but in your case you may benefit from installing a small anti rotation pin on the v-band flange. We use them all the time on turbos.

[TimS]

More like this I believe.  Need slip fit collector though.

https://www.summitracing.com/parts/vpe-10340?seid=srese1&gclid=EAIaIQobChMI1uCVr7SJ8gIVQYSGCh2zyAwgEAQYASABEgI7u_D_BwE

Edited July 29, 2021 by TimS

[MR2 Biohazard]

I had a bunch of cracking on my exhaust in the past and fixed it with flanges that held it in multiple places. This way the stress was not all on the bellows. I try to make sure I do not go more than 2' without some type of hanger/flange to hold it at that point. I also weld the flange around the pipe so it has a larger area to support the exhaust. On my front header I go 1' down and support flange, to a V band, bellow, 10' down to another hanger/flange, V band to muffler that has another flange/hanger. With solid engine mounts the more hangers the better.