Going Catless! - Let's Discuss / Inform and Educate

Checkmate1 · 08-28-2019, 09:47 AM

Fully aware this topic has been discussed to death.

I get the main downside being the 'smell' that permeates from a Catless setup.

That being said, as someone who wants to get headers on a Forced Induction car, what is my choice for reliability?

Our cars being supercharged run extremely hot with up to 2000' in thermal energy expended from the LT4.

From what I understand, these forced induction cars chew through Cats when modified via LT headers, tune etc....

A recent video from CSP showed even the Kooks/GESI Green Cats being annihilated...

I haven't heard a single Catback exhaust system on the ZL1 that brings out the raw, guttaral sounds of our pushrods. My favorite sounds are always those with LT headers.

I am not looking for a massive HP increase. I am quite happy with my 650HP/TQ. My main priority is Sound and not leaving anything on the table.

My average use and expected use is 70% Street / 30% Road Course.

I live in MD which requires emissions testing however via OBD code.

Let's discuss.

gotswap · 08-28-2019, 10:17 AM

In regards to the heat issues and cats. Couldn't we just move them downstream a bit to help with the heat issue?

Rlhay2 · 08-28-2019, 10:34 AM

I'm catless with 800+rwhp.
Cats routinely fail above 650rwhp.
Corsa double helix X-pipe quells the rasp and it is full stealth with the butterflies closed on the muffler.
No smell issues either as there is an E85 station 3 miles from my house.

SJFGTO · 08-28-2019, 10:58 AM

1) Smell - yes it is there, bothers some, others not. Purely subjective. I don’t mind the smell, over time I rarely notice it. The benefit of no cats on a FI car with long tubes outweighs the annoyance.
2) Rasp - a bigger concern. Rasp is that rattle, slightly metallic sound under load. Some exhaust systems mitigate the rasp of a catless exhaust better than others. The ARH full length system is the most rasp free exhaust I have ever heard. Corsa systems do a pretty good job too.
3) Catless is worth 3-7 HP on most street builds that I have seen, not really a reason to do it.
4) Reliability- already covered in numerous threads. FWIW, I went catless because a cat failure is high risk catastrophic engine damage. No inspection where I live, so going catless just is cheap insurance.

parish8 · 08-28-2019, 11:05 AM

If you have no inspections I say go for it. If you don’t like the sound it is easy to adjust your set up. Sometimes I will weld in a little strait through bullet muffler to knock down the sound level a little.

SilverZl1 · 08-28-2019, 11:28 AM

I have 2” LT headers, no cats, and only added a couple of simple bullet resonators to the remaining stock exhaust as Parish8 mentioned to get rid of the rasp that is common with this setup. Doesn’t lessen the volume, just kills the rasp. I also pulled the NPP fuse so the flaps don’t close at cruising speeds. If you don’t pull the fuse and the flaps close at cruising speed you’ll hate the sound you get at partial throttle. I run E85 for the hp so don’t have the smell, but kinda liked the smell anyway.

nicktechla · 08-28-2019, 01:36 PM

It doesn't smell when you are moving

TheMailMan0 · 08-28-2019, 01:54 PM

Smell is not an issue for me, unless at a light with the windows down. I daily mine 30 miles each way dressed in a suit with the jacket sitting shot gun. If your windows are up, or moving with the windows down you'll never smell it.

Dysan911 · 08-28-2019, 08:46 PM

I was catless for a while until I just couldn't deal with the smell anymore. I went with a rather expensive set of Cats though. Vibrant Gesi green cats.

https://vibrantperformance.com/catal...358354e5ec019b

Quote:

GESI UHO-Series Catalytic Converter, 3" Inlet/Outlet x 4.5" O.D. x 7" Overall Length (rated for 500-850HP)

- Capable of withstanding up to 1500 deg F
- Ideal for forced induction applications, with no loss of HP
- Covered by a 5 y

I'm not sure how these compare to the kooks green cats though but I spent a good bit extra because these seemed to be a much higher quality.
Also, I recently got setup with a Flex Fuel tune so now Im thinking the smell probably wouldn't bother me. On E85 I'm probably closer to 650 rwhp.

GT-ER · 08-28-2019, 10:16 PM

Quote:

Originally Posted by Dysan911

I was catless for a while until I just couldn't deal with the smell anymore. I went with a rather expensive set of Cats though. Vibrant Gesi green cats.

https://vibrantperformance.com/catal...358354e5ec019b

I'm not sure how these compare to the kooks green cats though but I spent a good bit extra because these seemed to be a much higher quality.
Also, I recently got setup with a Flex Fuel tune so now Im thinking the smell probably wouldn't bother me. On E85 I'm probably closer to 650 rwhp.

Kooks green cats are GESI cats.

Dysan911 · 08-28-2019, 10:22 PM

Quote:

Originally Posted by GT-ER

Kooks green cats are GESI cats.

yeah I was just doing some research and it appears that is correct so I'm running the exact same ones that blew up at CSP.

Not good!

JonDaddy82 · 08-29-2019, 06:16 PM

I already have the Borla 60608 resonator in my 60606 mid-pipe, so I should be pretty well prepped when it's time for LT headers. This will be my first year in an inspection county, and from what I've heard they just plug into the OBD port...if that's the case then I'm golden.

Zigg L1 · 08-29-2019, 07:50 PM

Quote:

Originally Posted by JonDaddy82

I already have the Borla 60608 resonator in my 60606 mid-pipe, so I should be pretty well prepped when it's time for LT headers. This will be my first year in an inspection county, and from what I've heard they just plug into the OBD port...if that's the case then I'm golden.

Does that Borla resonator clamp right up to my Borla catback? What is the Diameter? Obviously the catback is 3". I just installed the Kooks headers to my Borla catback Stype and holy rasp! Changed the sound completely and made it super loud. Looking to tone it down with the resonator.

SilverZl1 · 08-29-2019, 08:16 PM

Before I put the bullet resonators on, I went nuts researching high flow cats. I figured the cats would manage the rasp without robbing too much power and as a byproduct would deal with the smell. I actually bought the vibrant ultra high flo’s, had them in-hand, but was convinced to go with the simple bullets by the shop (I really mean simple, as in they were laying around the shop and they gave them to me. Don’t even know who makes them).

The vibrant cats are impressive. They have an ultra high flo line that can (as they say) handle much higher heat than the “normal” GESI or Kooks green cats. I couldn’t find any examples of them failing like green cats (and trust me I looked). I moved on from that obsession once I put the bullets on and life was good, but would be very interested to know if anyone has ever heard of a Vibrant cat failing?

08-28-2019, 09:47 AM	#1
Checkmate1 Drives: Garnet Red / ZL1 1LE Join Date: Apr 2016 Location: Bel Air, MD Posts: 492	Going Catless! - Let's Discuss / Inform and Educate Fully aware this topic has been discussed to death. I get the main downside being the 'smell' that permeates from a Catless setup. That being said, as someone who wants to get headers on a Forced Induction car, what is my choice for reliability? Our cars being supercharged run extremely hot with up to 2000' in thermal energy expended from the LT4. From what I understand, these forced induction cars chew through Cats when modified via LT headers, tune etc.... A recent video from CSP showed even the Kooks/GESI Green Cats being annihilated... I haven't heard a single Catback exhaust system on the ZL1 that brings out the raw, guttaral sounds of our pushrods. My favorite sounds are always those with LT headers. I am not looking for a massive HP increase. I am quite happy with my 650HP/TQ. My main priority is Sound and not leaving anything on the table. My average use and expected use is 70% Street / 30% Road Course. I live in MD which requires emissions testing however via OBD code. Let's discuss. __________________ #SAVETHEMANUALS Last edited by Checkmate1; 08-28-2019 at 11:09 AM.

08-28-2019, 10:34 AM	#3
Rlhay2 Drives: 2017 ZL1 Join Date: Mar 2014 Location: DFW, TX Posts: 302	I'm catless with 800+rwhp. Cats routinely fail above 650rwhp. Corsa double helix X-pipe quells the rasp and it is full stealth with the butterflies closed on the muffler. No smell issues either as there is an E85 station 3 miles from my house. Last edited by Rlhay2; 08-28-2019 at 01:35 PM.

08-28-2019, 10:58 AM	#4
SJFGTO Oh Oh it's Friday Night! Drives: 2018 ZL1 1LE Nightfall Gray Join Date: Jan 2018 Location: Walton Woods Posts: 1,061	1) Smell - yes it is there, bothers some, others not. Purely subjective. I don’t mind the smell, over time I rarely notice it. The benefit of no cats on a FI car with long tubes outweighs the annoyance. 2) Rasp - a bigger concern. Rasp is that rattle, slightly metallic sound under load. Some exhaust systems mitigate the rasp of a catless exhaust better than others. The ARH full length system is the most rasp free exhaust I have ever heard. Corsa systems do a pretty good job too. 3) Catless is worth 3-7 HP on most street builds that I have seen, not really a reason to do it. 4) Reliability- already covered in numerous threads. FWIW, I went catless because a cat failure is high risk catastrophic engine damage. No inspection where I live, so going catless just is cheap insurance. __________________ 2018 Camaro ZL1 1LE NFG; ARH 2” headers, catless mids, ARH full exhaust, Lingenfelter 18% lower pulley, ATI Harmonic Balancer, Roto-fab CAI, EE-catch can, TM ported TB, NX Lid, BMR strut tower brace. Aeroforce dual pod interceptor gauges. Tuned by Vengeance Racing!!! 644 HP @ 6250 rpm / 689 trq @ 3660 rpm Four that wanna own me Two that wanna stone me One says she's a friend of mine...

08-28-2019, 11:05 AM	#5
parish8 Drives: 17 SS a8 Join Date: Feb 2010 Location: omaha Posts: 1,678	If you have no inspections I say go for it. If you don’t like the sound it is easy to adjust your set up. Sometimes I will weld in a little strait through bullet muffler to knock down the sound level a little. Attached Images __________________ dropped a valve in the 6.2. now running a drop in rods and piston 5.3 best et 5.83@121 with the 5.3 http://www.camaro6.com/forums/showthread.php?t=465472

08-28-2019, 01:36 PM	#7
nicktechla Drives: 2012 Porsche 911 Turbo S Join Date: Jan 2017 Location: Los Angeles, CA Posts: 1,776	It doesn't smell when you are moving __________________ IG: 2fast2nick -- Current -- 2012 Porsche Turbo S - PDK - Basalt Black Metallic -- Past -- 2017 Camaro ZL1 Coupe - Red Hot - A10, PDR - HRE P101 2015 Mustang GT PP - Whipple Supercharger

08-28-2019, 10:17 AM	#2
gotswap Drives: 2019 ZL1 Crush Join Date: Jan 2019 Location: Colorado Springs Posts: 564	In regards to the heat issues and cats. Couldn't we just move them downstream a bit to help with the heat issue?

08-28-2019, 11:28 AM	#6
SilverZl1 Drives: 2018 ZL1 Join Date: Mar 2019 Location: Houston, Tx Posts: 31	I have 2” LT headers, no cats, and only added a couple of simple bullet resonators to the remaining stock exhaust as Parish8 mentioned to get rid of the rasp that is common with this setup. Doesn’t lessen the volume, just kills the rasp. I also pulled the NPP fuse so the flaps don’t close at cruising speeds. If you don’t pull the fuse and the flaps close at cruising speed you’ll hate the sound you get at partial throttle. I run E85 for the hp so don’t have the smell, but kinda liked the smell anyway.

08-28-2019, 01:54 PM	#8
TheMailMan0 Drives: 2018 Camaro ZL1 Join Date: Mar 2019 Location: FL Posts: 34 View My Garage	Smell is not an issue for me, unless at a light with the windows down. I daily mine 30 miles each way dressed in a suit with the jacket sitting shot gun. If your windows are up, or moving with the windows down you'll never smell it. __________________ ARH 2" Long system to stock suitcase / VVT3 cam/ RotoFab Big Gulp/ IW Balancer with 9.1 Ring/ Stock Upper/ HD Belt/ NGK Plug Set/ Taylor Wire set with Head Shields/ Tuned at Lashway Motorsports

08-29-2019, 06:16 PM	#12
JonDaddy82 Drives: 2018 ZL1 Coupe NFG M6 Join Date: May 2017 Location: Nolensville, TN Posts: 618	I already have the Borla 60608 resonator in my 60606 mid-pipe, so I should be pretty well prepped when it's time for LT headers. This will be my first year in an inspection county, and from what I've heard they just plug into the OBD port...if that's the case then I'm golden. __________________ 1989 Forumla 350 WS6 <- High School 2000 Trans Am Firehawk <- After High School 2017 Colorado Z71 <- Daily 2018 ZL1 M6 <- Not Daily

08-29-2019, 08:16 PM	#14
SilverZl1 Drives: 2018 ZL1 Join Date: Mar 2019 Location: Houston, Tx Posts: 31	Before I put the bullet resonators on, I went nuts researching high flow cats. I figured the cats would manage the rasp without robbing too much power and as a byproduct would deal with the smell. I actually bought the vibrant ultra high flo’s, had them in-hand, but was convinced to go with the simple bullets by the shop (I really mean simple, as in they were laying around the shop and they gave them to me. Don’t even know who makes them). The vibrant cats are impressive. They have an ultra high flo line that can (as they say) handle much higher heat than the “normal” GESI or Kooks green cats. I couldn’t find any examples of them failing like green cats (and trust me I looked). I moved on from that obsession once I put the bullets on and life was good, but would be very interested to know if anyone has ever heard of a Vibrant cat failing?

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