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BionicBalls · Joined: 05 Jan 2009 Posts: 642 Location: Charlotte, NC

My exhaust keeps breaking the welds loose at the catalytic converter. I've got headers and 2.25" stainless steel pipe all the way back. Magnaflow Hi flow cat and a flowmaster super 44 muffler.

I've got some popping in my exhaust when I decelerate. I'm pretty sure this is causing the welds to break loose.

I've got a flex pipe on the way, think this will absorb the vibrations caused by the exhaust popping?

I think the popping will lessen as soon as I set the A:F ratio correctly.
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1980 924 NA
1982 931

Paul · Posted: Sat Jul 02, 2011 1:57 pm Post subject:

No part of the exhaust system is attached to the body, correct? Are all your hangers from the CAT back intact?
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

BionicBalls · Joined: 05 Jan 2009 Posts: 642 Location: Charlotte, NC

Not attached to the body at any point. All the hangers are intact and in good condition. That's what makes this so frustrating.
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1980 924 NA
1982 931

leadfoot · Posted: Sat Jul 02, 2011 9:17 pm Post subject:

how are your motor mounts then?
Stu
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Time to try a different muffler shop?
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Joes924Racer · Posted: Sun Jul 03, 2011 4:18 am Post subject:

That is freakin amazing that the welds are breakin maybe adjust the afm
so it dont pop..
Good luck with the flex pipe.Ill bet its the fix.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Popping is probably from air leaking into the system from poorly sealed pipes/joints.

Try adding another hanger near the front of the exhaust and of course the flex coupling will help quite a bit.

Bad motor mounts will exacerbate the vibrations and make the exhaust more prone to cracking and breaking.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

BionicBalls · Joined: 05 Jan 2009 Posts: 642 Location: Charlotte, NC

I adjusted the throttle body adjustment screw to let more air in and it has reduced the popping significantly. I had been told that the popping was due to the lack of back pressure from having headers and a larger exhaust piping. true? I'll be adding the flex pipe in and I'll see if I can't add another hanger as well.

Every time I've had a bad motor mount on a car before, I could feel the engine vibrating. That's not happening here, engine feels smooth. I Visually inspected the driver's side mount and it's not cracked or broken. The passenger side one is a shock type mount, how would I go about checking it?
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1980 924 NA
1982 931

DOCO · Posted: Tue Jul 05, 2011 1:49 am Post subject:

you need 2 people one to drive car and one to hang on the hood...Just kidding!!apply parking brake,put car in first and let out clutch and have other helper look at mount and see if its sperated,put in reverse for other side edit ;if its automatic just brake torque in fwd and reverse
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Doco "where am i going and why am i in this handbasket"author unknown
79 924 N/A "Webster"
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/______\
[+]___[+]
\0 924 0/
[__]..[__]
"WEBB STR"

Min · Posted: Tue Jul 05, 2011 3:28 am Post subject:

What kind of filler is your stainless exhaust system being welded with?

Min
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Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

BionicBalls · Joined: 05 Jan 2009 Posts: 642 Location: Charlotte, NC

I'm tired of dealing with the muffler shop so today I did it myself. I unbolted the center section of my exhaust. I ground down all the welds and started from scratch. I cut out a section and fit in the flex pipe. Re-welded the cat. Bought a new header gasket and exhaust donut.

I removed the o2 sensor and set the A/F ratio there using my gunson. Still some popping, but alot less.

I've got a mig welder and I use what ever wire my dad buys for it. It is some good stuff. We bought some cheap shit once before, and it fed poorly, got poor penetration and ugly welds no matter how slow we fed it.

So far everything is sounding good, I'll report back in a week.

New problem is a pinhole in the seam of my overflow tank that's spraying a small bit of coolant everywhere. Tried plastic welding it, but it's not containing it. I'm going to try one more time, but may have to just replace it.
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1980 924 NA
1982 931

Min · Posted: Tue Jul 05, 2011 4:40 pm Post subject:

BionicBalls · Joined: 05 Jan 2009 Posts: 642 Location: Charlotte, NC

Makes Sense. I'll look into it. Hopefully everything holds though.
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1980 924 NA
1982 931

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

The original exhaust used a hanger at the rear end of the downpipe that supports the downpipe and the front of the cat (and there was an adapter between the downpipe and the cat).

Does your header have that hanger? If not, the exhaust would probably break where you descibe over and over again.

BionicBalls · Joined: 05 Jan 2009 Posts: 642 Location: Charlotte, NC

My header does not have a hanger. That is going to be the next thing I do even if the exhaust doesn't break open again.

Thanks for the info gohim.
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1980 924 NA
1982 931