exhaust without cats - ZR-1 Net Registry Forums

WARP TEN · 07-20-2013

I am contemplating removing cats from my exhaust system. No emissions testing in Illinois for our Zs. I currently have headers, Corsa, and ceramic cats. I am aware of the performance gains and I know whatever exhaust system is in place will be louder. What I wondered about is does the exhaust smell bad on start up and later when hot? I have heard people say so but I have not experienced it. What is it, an excessively rich mixture on startup? Good, bad, not important? All opinions welcome -- Bob

FU · 07-20-2013

Have to get a chip cut or the exhaust smell will be horrible. Any power gains will be minor at best.
I'd consider just going out and replace the ceramic cat's with some new metallic substrate cats. The met. cat's arent expensive , google can help out.

Kevin · 07-20-2013

I drove a headers no cats and corsa 90 once. Sounded fine if you like corsas. Smelled fine too. But you really should get a retune

efnfast · 07-20-2013

I have a 90, so no exaust valve seals, headers, no cats and Marc's chip. You can definately smell the unburned fuel- makes me horny, if you're into that kinda thing.

WARP TEN · 07-20-2013

Quote:

Originally Posted by efnfast

I have a 90, so no exaust valve seals, headers, no cats and Marc's chip. You can definately smell the unburned fuel- makes me horny, if you're into that kinda thing.

My tongue is hanging out and I am panting just thinking about it....

VetteVet · 07-21-2013

The PID (Proportional/Integral/Differential) control system is always going to swing lean and rich above and below stoichiometric ratio. The cats absorb the unburned hydrocarbons during the rich swings and burns them off in the cats when the excess oxygen is present during the lean swings. When cats are eliminated, there is nothing to catalyze the unburned hydrocarbons produced during the closed loop rich swings. Unless you are willing to run open loop full time or are willing to tweak the O2 crossover point so that you always run on the lean side, a car without cats will always have an unburned fuel smell that is obvious to all other vehicles in your vicinity (think old school pickup trucks thats you have pulled up behind in traffic that have carb problems, you know, the ones that burn your eyes.) The latest technology cats will clean up your emissions with minimal (think 1%) HP loss. Rant over!

Jep

RICKYRJ1 · 07-21-2013

I have run no cats with SS headers and Corsa exhaust for the past 3 yrs with no smell and no problems. Sounds great imho

mike100 · 07-21-2013

I adapted my headers with slip on SW parts to connect to headers and it is true- the car smells rich all of the time (just like first start in the morning before the cats light off and start functioning).

I plan to trim the collector back some and install 3" LS7 Cats if they will fit under the heat shielding. They are full density oem style substrate and I'm confident they will do a great job compared to various inexpensive high flow cats or nothing at all.

The car stands out too much in Cali with uncatalyzed fumes pouring out the back at idle and low load conditions. I expect the noise level will be brought down a notch as well with the cats installed which would be nice.

ZZZZZR1 · 07-21-2013

Quote:

Originally Posted by RICKYRJ1

I have run no cats with SS headers and Corsa exhaust for the past 3 yrs with no smell and no problems. Sounds great imho

I have corsa and no cats as well... I do end up with a little smell, but its not too bad. My car will be wearing historic tags come January too!!! (Then I can legally drive without cats!)

David

RICKYRJ1 · 07-21-2013

Does anybody know why I have no smell whatsoever? Mark H. did the performance work.

07-20-2013	#1
WARP TEN Join Date: Apr 2007 Location: Lake Bluff, IL Posts: 2,036	exhaust without cats I am contemplating removing cats from my exhaust system. No emissions testing in Illinois for our Zs. I currently have headers, Corsa, and ceramic cats. I am aware of the performance gains and I know whatever exhaust system is in place will be louder. What I wondered about is does the exhaust smell bad on start up and later when hot? I have heard people say so but I have not experienced it. What is it, an excessively rich mixture on startup? Good, bad, not important? All opinions welcome -- Bob __________________ 2016 Long Beach Red Z06 #10281 "POPS Z" 1995 Polo Green #409 "WARP TEN"--Haibeck 350/510 package, 4.10s, Hurst, Stock Exhaust with QTP Cutouts --Sold but still running strong 1993 Quasar Blue #161 "HIL KING" --Sold but still running strong, now with more than 120,000 miles 1967 Marlboro Maroon/Saddle Corvette Coupe 300 hp/4-spd --Sold a long time ago ZR-1 Net Registry Founding Member #95 NCM Lifetime Member Favorite Quote--Attributed to Mickey Thompson: "Too Much Horsepower is Almost Enough"

07-20-2013	#2
FU Join Date: Mar 2004 Location: Found Member Posts: 4,346	Re: exhaust without cats Have to get a chip cut or the exhaust smell will be horrible. Any power gains will be minor at best. I'd consider just going out and replace the ceramic cat's with some new metallic substrate cats. The met. cat's arent expensive , google can help out. __________________ Frank Urbo. NCM Lifetime member # 982 Registry Founding # 237

07-20-2013	#3
Kevin Join Date: Jun 2005 Location: pittsburgh Posts: 4,633	Re: exhaust without cats I drove a headers no cats and corsa 90 once. Sounded fine if you like corsas. Smelled fine too. But you really should get a retune __________________ It's not the car, it's the people - Doug Johnson 90 r/r "KEYS ON" nick named "T.L.B"

07-20-2013	#4
efnfast Join Date: Nov 2011 Location: Dunbarton NH Posts: 7,256	Re: exhaust without cats I have a 90, so no exaust valve seals, headers, no cats and Marc's chip. You can definately smell the unburned fuel- makes me horny, if you're into that kinda thing.

07-21-2013	#6
VetteVet Join Date: Jan 2009 Location: Mandeville, LA Posts: 340	Re: exhaust without cats The PID (Proportional/Integral/Differential) control system is always going to swing lean and rich above and below stoichiometric ratio. The cats absorb the unburned hydrocarbons during the rich swings and burns them off in the cats when the excess oxygen is present during the lean swings. When cats are eliminated, there is nothing to catalyze the unburned hydrocarbons produced during the closed loop rich swings. Unless you are willing to run open loop full time or are willing to tweak the O2 crossover point so that you always run on the lean side, a car without cats will always have an unburned fuel smell that is obvious to all other vehicles in your vicinity (think old school pickup trucks thats you have pulled up behind in traffic that have carb problems, you know, the ones that burn your eyes.) The latest technology cats will clean up your emissions with minimal (think 1%) HP loss. Rant over! Jep

07-21-2013	#7
RICKYRJ1 Join Date: Dec 2005 Location: Tinton Falls, NJ Posts: 1,177	Re: exhaust without cats I have run no cats with SS headers and Corsa exhaust for the past 3 yrs with no smell and no problems. Sounds great imho

07-21-2013	#8
mike100 Join Date: Feb 2011 Location: San Marcos CA Posts: 1,802	Re: exhaust without cats I adapted my headers with slip on SW parts to connect to headers and it is true- the car smells rich all of the time (just like first start in the morning before the cats light off and start functioning). I plan to trim the collector back some and install 3" LS7 Cats if they will fit under the heat shielding. They are full density oem style substrate and I'm confident they will do a great job compared to various inexpensive high flow cats or nothing at all. The car stands out too much in Cali with uncatalyzed fumes pouring out the back at idle and low load conditions. I expect the noise level will be brought down a notch as well with the cats installed which would be nice.

07-21-2013	#10
RICKYRJ1 Join Date: Dec 2005 Location: Tinton Falls, NJ Posts: 1,177	Re: exhaust without cats Does anybody know why I have no smell whatsoever? Mark H. did the performance work.