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exhaust popping

Hey guys,
just put in fabspeed single out exhaust to an otherwise stock 87 930. the mod made a huge difference in power. when I pulled the cat out it was severely damaged sounds like broken glass in there. The concern I have now is that I have a tremendous amount of crackling and popping only when decelerating and downshifting. I have heard this is normal, but I didn't really notice it with the stock exhaust. It sounds incredible but can't help but wonder if something is wrong with it. Should I be concerned, or just enjoy it? Also what do I need to do with the line that ran from the cat via metal pipe to a rubber hose on the right hand side of the engine, I have it disconnected from the rubber hose, but it is not plugged, anyone know what that line goes to, and what I should do with it?

Last edited by e170drvr; 02-16-2007 at 04:22 PM..
Old 02-16-2007, 04:15 PM
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Popping is simply the unburnt fuel being ignited in the headers and you can hear it more with the free flowing muffler... the OEMmuffler would have muffled it out. Just enjoy it! Sounds wicked IMO
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Old 02-16-2007, 04:48 PM
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yes it's very anti-social all that popping and burbling... and that's the way I like it
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Old 02-16-2007, 04:53 PM
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Ok, thats a huge relief, because if something was wrong with it, I would hate to have to fix it. I love it. thanks guys!
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Old 02-16-2007, 04:56 PM
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My wife says it is so obnoxious that she won't drive the car anymore. Hmm, wish I did it sooner!
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87 930 Coupe Red, K27S, Kokeln IC, Rarlyl8 Headers system, Tial 46MM, .9 Bar. "Lola"

81 911SC Coupe Guards Red, Stock. "Zippy"
Old 02-16-2007, 04:57 PM
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Quote:
Originally posted by e170drvr
My wife says it is so obnoxious that she won't drive the car anymore. Hmm, wish I did it sooner!
LMAO!
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Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
Old 02-16-2007, 05:06 PM
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*Sometimes* this can be caused by too rich an idle fuel mixture.
Local shop had a few of these cases -
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Old 02-17-2007, 05:40 PM
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Does your car still have an air pump? This will cause after fire with the cat removed.
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Old 02-17-2007, 05:56 PM
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thank you 930turbo, I didn't think of that. Just checked, and my pump is still intact, however the belt is extremely loose. any harm in cutting the belt? I have heard that it can damage the pump if the belt is removed (not really sure I care that much, but I am having trouble understanding how an accessory that is not being driven can be damaged. If the belt is off it's not going to do anything, right? unless disuse is how it is damaged. and should the line that goes to the cat that used to be there be plugged, if so how. looks like 1/2" rubber tube. really appreciate your help guys
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81 911SC Coupe Guards Red, Stock. "Zippy"
Old 02-18-2007, 12:43 AM
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Perhaps the exhaust may run up the lines to the pump without air being driven TO the pump? Makes sense to me, but this is only a guess.

I think your popping is actually pretty normal, and probably nothing to be concerned about.

Maybe post a sound/video file to You Tube - (it can be pretty big), this way we can hear for ourselves for a better analysis for you.
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Old 02-18-2007, 07:07 AM
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The pump would be damaged by sitting stationary. The after fire is caused by the conbination of residual fuel, compliments of your CIS, hot exhaust components and the fresh air provided by your air pump. These ingredients were processed inaudibly by the CAT prior to removal. The noise will never go completely away but if it's currenty obnoxious, the removal of fresh air will help.
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Past rides: '74 914 1.9 liter twin plugged track car, '83 928S, '87 924S, '75 911S w '78 ROW 3.0, '72 911T, '70 911T and various other insignificant domestic examples. Happiness is a grey tailpipe! Turbo lag......it's worth the wait!
Old 02-19-2007, 05:42 PM
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Thank you 930, checked yesterday, the pump pully is not even moving due to the extremely loose drive belt. would it help if I plugged the hole in the line that goes to the cat? Also it seems that the car might be running pretty rich, I get a really strong odor since I removed the cat. wondering if I should check the o2 sensor and get the co adjusted. as Craig said maybe if it is running too rich, that could cause the more than normal popping.
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81 911SC Coupe Guards Red, Stock. "Zippy"
Old 02-19-2007, 06:13 PM
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