exhaust without cats

[WARP TEN]

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]

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]

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]

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]

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]

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]

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]

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]

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!)

:cheers:

David

[RICKYRJ1]

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

[Anniv88]

Marc H. did all my work. Top end package, headers, Borla, no cats, and
tune. Never any smell. :dancing

[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.

On that note, my daughter was behind me today getting on the highway. I punched it in second and rowed up to forth. She called me on the two way redio's we had and told me how much I offended her nose. Of course she new nothing of this post. Her windows were up, and the air was on. -Steve

[PhillipsLT5]

you already answered your ?

[Corbusa]

Has anyone not used the fake cats in the OBX system and replaced them with real cats? and will everything still bolt up to the original exhaust pipes / H pipe.? Also if all I'm going to lose is 1% hp I might as well have them on.

[WARP TEN]

Marc H. did all my work. Top end package, headers, Borla, no cats, and
tune. Never any smell. :dancing

Good to know--Thanks

[Daniel_Mc]

Not cats on our 91 LT's with a stock system a bit raspy and not a smell that I ever noticed. Now LT's with B&B with X pipe no real smell either but still not loud enough for me :icon_scra

-Daniel

[WARP TEN]

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

Hey Jep--
Not a rant--you are correct based on my general experience although as others note the smell can be mitigated by a bit of tuning. Of course I come from the days when we used to tune cars based on the color of the spark plugs and the smoke from the exhaust!--Bob

[BigJohn]

Smoke?
Like a blown headgasket?
Like bad valve seals?


In the old old old days the inside of your tail pipe was white not black.

There I go again, anyway I forgot!

:neutral:

[DennisC]

Hows is that legal David because of age of vehicle?

[ZZZZZR1]

Hows is that legal David because of age of vehicle?

In 20 years we get historic tags in Maryland

:salute:

David

[DennisC]

Thought so Texas tags are classified as Classic Car tags

[Fully Vetted]

Thought so Texas tags are classified as Classic Car tags

And isn't it 25 years in Texas?

BTW...No cats, Corey tune, no smell.