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Old 01-05-2011, 01:16 AM   #1
noobwithaquestion
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Member#: 268519
Join Date: Dec 2010
Location: Portland, OR
Vehicle:
2003 2.5 RS
Silver

Default Why do I have 2 cats?

When reading this keep in mind I'm new to Subarus. I was installing my new Borla headers (I wish I knew they had a cracking issue before I bought them) and I noticed that there were 2 catalytic converters on my 2k3 2.5RS. Why? Would these cars not pass smog with one cat?
My second question to those who know, what's the thing on my midpipe, the one after the second car and before the round resonator?
My last question, is the WRX midpipe the same length as the 2.5RS? I know the flanges need to be rotated but besides that is it the same length?

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Old 01-05-2011, 09:54 AM   #2
Samirr76
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Member#: 4835
Join Date: Mar 2001
Chapter/Region: Tri-State
Location: Fl33tw00d, PA
Vehicle:
2003 Baja 5MT
Yellow w/ 220,000 miles

Default

Sure, it would probably pass smog with just one cat, but havnig an extra cat allows the vehicle to pass even higher smog standards, such a LEV, SULEV, PZEV, etc. and these are a benefit to the environment as well as a selling point for the vehicles. its is common for most new vehicles to have at LEAST two cats. My 2002 WRX came with THREE cats from the factory.
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Old 01-05-2011, 08:08 PM   #3
Rudgers73
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Member#: 141433
Join Date: Feb 2007
Chapter/Region: MAIC
Location: Rochester, NY
Vehicle:
2006 Impreza 2.5i
Obsidian Black

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yes, that third "thing" might be a third cat. Behind the second o2 sensor... My 99 Legacy GT had a third cat and after some reading I found that they put that on there to pass the California emissions sniffer test. I was going to rip that one off as soon as I needed new exhaust pieces, but I ended up totaling the car before anything rusted out... derp
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Old 01-06-2011, 12:41 AM   #4
williaty
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Join Date: Sep 2004
Chapter/Region: MWSOC
Location: Delaware County, Ohio
Vehicle:
2005 2.5RS Wagon
Regal Blue Pearl

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On your car, both cats are in the cat pipe. The two bulges on the midpipe are merely resonators.
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Old 01-06-2011, 01:42 AM   #5
Jessekrs123
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Join Date: Jan 2010
Chapter/Region: NESIC
Location: Oakville CT
Vehicle:
1993 Legacy Sedan
1984 BRAT

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Your car is a ***** magnet. Sorry, couldn't resist.

Anyways, as Williaty said, those other bulges are resonators, keeping your exhaust quiet and less raspy.
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Old 01-06-2011, 05:33 AM   #6
noobwithaquestion
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Location: Portland, OR
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Silver

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Cool, that is good to know. I'm having a custom mid pipe done in 2.25" and I'm going with a single resonator to keep the raspiness down but still retain some sound. That should go well with the STI axle back I just put on.
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Old 01-10-2011, 12:34 PM   #7
dblotii
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Join Date: Mar 2006
Location: Central NY
Vehicle:
2006 2.5i

Default close-coupled cat

the catalytic converter closes to the engine is called the close-coupled cat and is there to light-off as quickly as possible to reduce emissions in the first minute following a cold-start.

Dave
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