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modify 931 exhaust
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1000
Location: The Netherlands

PostPosted: Fri Jan 27, 2017 6:39 am    Post subject: modify 931 exhaust Reply with quote

My front section of the exhaust is scratch and dented because of al the speed bumps here in Holland

With my rebuild engine I have a new exhaust manifold and turbo hotside, which I don't want to damage.

Can I put a flexible piece in the front section, or are temperatures there to high ?

With the flexible piece, I hope If the exhaust hits a bump my turbo/ exhaust manifold won't be damaged.


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ideola  



Joined: 01 Oct 2004
Posts: 15489
Location: Woodstock IL

PostPosted: Fri Jan 27, 2017 6:57 am    Post subject: Reply with quote

Stainless exhaust expansion joints


Put one in the j-pipe, and put one in the main down pipe. (Different diameters, of course).

Here's how I did my j-pipes:

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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1000
Location: The Netherlands

PostPosted: Fri Jan 27, 2017 7:20 am    Post subject: Reply with quote

ok thanks, but why one in the wastegate pipe, what is the benefit ?
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Cédric  



Joined: 27 Aug 2004
Posts: 1681
Location: Sweden

PostPosted: Fri Jan 27, 2017 7:53 am    Post subject: Reply with quote

I did exactly like your image, but maybe a bit further down, works great and makes fitment of the exhaust system so much easier. Probably puts a lot less stress into the hardware as it havr some flex when things heat up. Can get some pics if you wish!
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ideola  



Joined: 01 Oct 2004
Posts: 15489
Location: Woodstock IL

PostPosted: Fri Jan 27, 2017 7:59 am    Post subject: Reply with quote

Dutch924-racer wrote:
why one in the wastegate pipe, what is the benefit


Because:
Cédric wrote:
makes fitment of the exhaust system so much easier


And because many of the J-pipes I've removed have broken where they connect to the exhaust manifold. The flex coupler serves as an expansion joint that allows the metal to expand and contract, minimizing stress on both of the attachment points.
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1490
Location: Not Detriot - NMI

PostPosted: Fri Jan 27, 2017 8:05 am    Post subject: Reply with quote

Their is a whole lot to go wrong with the 931 exhaust due to their being so many hard mount points, and everything being hard mount..

First you have the header-turbine housing-bearing housing-blockmount-block..
For that I like to install all of the components loose except for the header to head, hot housing just snug enough to be able to turn it a bit.. Then get it all in there and start finger tightening everything so all of the components are sitting flat on their mounts, tighten up the hot housing a bit so it stays and then pull it back out to finish tightening the hot housing to where it liked to be, then you can put the turbo back in and cross tighten the whole thing in position between the block bearing housing mount and turbine housing..

And then you have the downpipe-WG-Jpipe-header.. All with no room for error..

I like the idea of those flex couplers in the J-pipe, WG dump pipe, and downpipe..

That would definitely reduce stress to the turbo and exhaust manifold, but would only doing 1 possibly increase the stress load of the other 2?

If you do it just to the downpipe then the WG circuit will bear it all on it's own, mix and match vise versa any way and you'd be putting all of the stress on the remaining component(s) instead of sharing it evenly..

Maybe just one after the cat, or after the WG dump meets the downpipe, to isolate everything that is bolted to the engine from the rest of the exhaust, or all 3 before that point..
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ideola  



Joined: 01 Oct 2004
Posts: 15489
Location: Woodstock IL

PostPosted: Fri Jan 27, 2017 9:25 am    Post subject: Reply with quote

Fasteddie313 wrote:
WG dump pipe

His car is Euro, so he doesn't have the w/g dump pipe...

I'm not even sure it's necessary if you do the j-pipe AND the main down pipe.
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gegge  



Joined: 27 Jul 2007
Posts: 1020
Location: Sweden

PostPosted: Fri Jan 27, 2017 10:00 pm    Post subject: Reply with quote

I have a flexible coupler like the rest of you, but after the ROW Y-joint from the WG. Reason was fitment issues alone with that long muffler.

Like the J-pipe solutionon a ROW better than putting a flexible coupler earlier in terms of reducing tension from heat. Some flexibilty sounds like a good thing. The flexible coupler should be a straight as possible with a straight flow.

Speed-bump related dents should be adressed in another way I belive. A low hanging exhaust will still hit the tarmac/concrete with or without a flexible coupler. If you are trying to raise the downpipe with a flexible coupler instead of just cut´n´weld - it sounds right.

Next set-up is based on the US WG screamer since I belive the dual exhaust have larger capacity an less backpressure.
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Cédric  



Joined: 27 Aug 2004
Posts: 1681
Location: Sweden

PostPosted: Fri Jan 27, 2017 10:06 pm    Post subject: Reply with quote

If you do it on the J-pipe you still have a hard mounted WG (bolted to the torque tube) and turbine housing, but of course it makes things a bit more flexible since you can adjust the WG position a bit (the holes are oval if I remember correctly). The whole point of it for me was do decouple the turbine outlet and WG outlet geometry wise, otherwise its a tolerance nightmare Small change of the two flanges to line up perfectly.

I had to wrap a steel sheet around my flexi hose though since it has some damage from speed bumps etc..
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morghen  



Joined: 21 Jan 2005
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Location: Romania

PostPosted: Sat Jan 28, 2017 12:31 am    Post subject: Reply with quote

My WG is not bolted to anything else but the pipe holding it.
It has been like this since 2007.
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ideola  



Joined: 01 Oct 2004
Posts: 15489
Location: Woodstock IL

PostPosted: Sat Jan 28, 2017 12:40 am    Post subject: Reply with quote

morghen wrote:
My WG is not bolted to anything else but the pipe holding it.
It has been like this since 2007.


Recipe for a broken J-pipe.
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morghen  



Joined: 21 Jan 2005
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Location: Romania

PostPosted: Sat Jan 28, 2017 1:08 am    Post subject: Reply with quote

True(or worse, manifold crack or head bolt strip), but hasn't happened yet(i think), and I'm on 270lb springs and 225/45/17 tires.

I'm also planning for some flexible insert just after the turbo.
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Sat Jan 28, 2017 1:16 am    Post subject: Reply with quote

It would be interesting to see if there's a way to put vibration dampers somewhere on the wastegate-to-torque tube bracket. I think that bracket is important, but the OEM solid mounting probably doesn't do the j-pipe welds any favors either.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1533
Location: Somerset, UK

PostPosted: Sat Jan 28, 2017 4:25 am    Post subject: Reply with quote

ideola wrote:
morghen wrote:
My WG is not bolted to anything else but the pipe holding it.
It has been like this since 2007.


Recipe for a broken J-pipe.


Not for me in the last 3 years. Broken j pipes are probably results of age, corrosion or impacts. Keep on top of maintenance and all is good.
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Sat Jan 28, 2017 4:34 am    Post subject: Reply with quote

Carrera RSR wrote:
Broken j pipes are probably results of age, corrosion or impacts.
The ones I've seen break (and there have been a lot...maybe a dozen or more) typically fail at the weld joint where the pipe is welded to the two bolt flange that attaches to the exhaust manifold. Less often, but still occasionally, I have seen similar weld failures at the four bolt flange where the j-pipe attaches to the wastegate.

The j-pipes are stainless, like the rest of the exhaust aft of the manifold and turbine, so corrosion is unlikely the cause of failure.

Carrera RSR wrote:
Keep on top of maintenance and all is good.
As a general rule, older cars on your side of the pond seem to be better maintained than over here. I can't quite account for why our US examples are so maligned and neglected.

Carrera RSR wrote:
Not for me in the last 3 years.
It just seems to me that the wastegate is really heavy, and to be cantilevered out there all on its own, and only supported by the two studs/nuts at the exhaust manifold port seems imprudent to me. I've not had any issues with any of the ones that I've put back together using the factory mount points at the torque tube, one of those builds is going on 10 years, and the other 6.

I suppose this is a classic case of YMMV.
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