Secondary cat removal - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

wootwoot · 05-29-2013, 01:25 AM

I just bought a P&L catted header and am trying to plan out the rest of my exhaust. What would be the result of removing the secondary cat in terms of smell and sound? I am planning on a nameless resonated front pipe and trying to figure out of I can get away with no second cat. How much louder will the resonated front pipe be without a cat? Will it smell?

reeves · 05-29-2013, 10:23 AM

I have a catted 4-1 header + resonated front pipe & overpipe + stock cat-back.. It's not very loud at all. If you get an aftermarket cat-back, all bets are off though. My CAI seems is louder than my exhaust at WOT.. can't really tell which sound is coming from where anymore though. It doesn't smell either with just the 2nd cat removed.

vtmike · 05-29-2013, 10:33 AM

If I understand it correctly, the second cat (one in the front pipe) is actually the primary one. The one in the header is there to help until the primary one warms up.

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jamesm · 05-29-2013, 10:47 AM

Quote:

Originally Posted by vtmike

If I understand it correctly, the second cat (one in the front pipe) is actually the primary one. The one in the header is there to help until the primary one warms up.

Sent from my SCH-I535 using Tapatalk 2

'primary' == 'first' as i understand it.

vtmike · 05-29-2013, 11:13 AM

I think your right. I could have sworn I read somewhere the second cat did most of the pollutant removal after warm and that was what I was basing the term primary on.

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wootwoot · 05-29-2013, 11:24 AM

Not so sure about that one guys. The people with the cat in the header removed complain about a nasty smell. I haven't read it to be the other way around yet...

Any other advice?

vtmike · 05-29-2013, 11:38 AM

I've heard people complain about the sound with the secondary removed on stock header with primary cat present. I believe the complaint was it's really raspy. A good high flow catted front pipe is supposed to flow pretty much equally well as uncatted.

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wootwoot · 05-29-2013, 11:42 AM

Cool. Catted it will be. Thanks.

05-29-2013, 01:25 AM	#1
wootwoot Senior Member Join Date: Jul 2012 Drives: FRS Location: Cali Posts: 1,558 Thanks: 188 Thanked 461 Times in 264 Posts Mentioned: 9 Post(s) Tagged: 0 Thread(s)	Secondary cat removal I just bought a P&L catted header and am trying to plan out the rest of my exhaust. What would be the result of removing the secondary cat in terms of smell and sound? I am planning on a nameless resonated front pipe and trying to figure out of I can get away with no second cat. How much louder will the resonated front pipe be without a cat? Will it smell?

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05-29-2013, 10:23 AM	#2
reeves Senior Member Join Date: Jul 2012 Drives: BRZ Location: ATL, GA Posts: 1,021 Thanks: 289 Thanked 397 Times in 265 Posts Mentioned: 13 Post(s) Tagged: 0 Thread(s)	I have a catted 4-1 header + resonated front pipe & overpipe + stock cat-back.. It's not very loud at all. If you get an aftermarket cat-back, all bets are off though. My CAI seems is louder than my exhaust at WOT.. can't really tell which sound is coming from where anymore though. It doesn't smell either with just the 2nd cat removed.

05-29-2013, 10:33 AM	#3
vtmike Senior Member Join Date: Jun 2012 Drives: Scion FR-S Location: Virginia Posts: 477 Thanks: 80 Thanked 134 Times in 103 Posts Mentioned: 13 Post(s) Tagged: 1 Thread(s)	If I understand it correctly, the second cat (one in the front pipe) is actually the primary one. The one in the header is there to help until the primary one warms up. Sent from my SCH-I535 using Tapatalk 2

05-29-2013, 11:13 AM	#5
vtmike Senior Member Join Date: Jun 2012 Drives: Scion FR-S Location: Virginia Posts: 477 Thanks: 80 Thanked 134 Times in 103 Posts Mentioned: 13 Post(s) Tagged: 1 Thread(s)	I think your right. I could have sworn I read somewhere the second cat did most of the pollutant removal after warm and that was what I was basing the term primary on. Sent from my SCH-I535 using Tapatalk 2

05-29-2013, 11:24 AM	#6
wootwoot Senior Member Join Date: Jul 2012 Drives: FRS Location: Cali Posts: 1,558 Thanks: 188 Thanked 461 Times in 264 Posts Mentioned: 9 Post(s) Tagged: 0 Thread(s)	Not so sure about that one guys. The people with the cat in the header removed complain about a nasty smell. I haven't read it to be the other way around yet... Any other advice?

05-29-2013, 11:38 AM	#7
vtmike Senior Member Join Date: Jun 2012 Drives: Scion FR-S Location: Virginia Posts: 477 Thanks: 80 Thanked 134 Times in 103 Posts Mentioned: 13 Post(s) Tagged: 1 Thread(s)	I've heard people complain about the sound with the secondary removed on stock header with primary cat present. I believe the complaint was it's really raspy. A good high flow catted front pipe is supposed to flow pretty much equally well as uncatted. Sent from my SCH-I535 using Tapatalk 2

05-29-2013, 11:42 AM	#8
wootwoot Senior Member Join Date: Jul 2012 Drives: FRS Location: Cali Posts: 1,558 Thanks: 188 Thanked 461 Times in 264 Posts Mentioned: 9 Post(s) Tagged: 0 Thread(s)	Cool. Catted it will be. Thanks.

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