exhaust without cats

[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

[ZZZZZR1]

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

[DennisC]

Hows is that legal David because of age of vehicle?

[ZZZZZR1]

Originally Posted by DennisC

Hows is that legal David because of age of vehicle?

In 20 years we get historic tags in Maryland



David

[DennisC]

Thought so Texas tags are classified as Classic Car tags

[Fully Vetted]

Originally Posted by DennisC

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.

[WARP TEN]

Originally Posted by 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

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!