This is going to be an odd question but its a unique situation. My car came with no cats or precats straight to the mufflers. I have the car in an enclosed communal garage and when I start it it stinks up the whole place really bad. If my understanding is correct, the precats are designed specifically to eliminate emissions on startup. Would putting them in solve my issue? I'm thinking something like this:

 

Basics!!! any codes? What year?? completely stock?? the older ECM platforms run a Rich AFR.
adding exhaust on the very restrictive TPI system. will let the car breath. the ECM will see this as a lean mix. then add more full creating a rich AFR. A counter tune is always WELCOMED.
My current sequential LT1 has full length headers, NO cats, H-back. or previous Holley stealth ram conversions. the exhaust smells great. But, I tune.

 

What year is your car (always helps to put that information in a thread)? Maybe enve add it to your "About Me" section of your User CP.

Only the early C4's had pre-cats along with a main cat. Does the car still have the AIR system?

I had installed headers and true duals on my old '87 and I never smelled anything like a rich fuel condition. It's possible that leaky/worn injectors and fouled plugs may be contributing to the smell. Try adding a can of Seafoam to your next tank fill up and see if that might help with cleaning the injectors.

 

Ever since my cats were removed it has smelled. Smells kinda like a lawn mower when cold and when it warms up the smell loses it's strength but the smell changes as the AFR leans out to stoich. Run it in an un-ventilated garage and your eyes will burn and tear up. Pretty normal, my motorcycles do the same thing as well as my old Camaro did.

 

1st make sure you are in tune.

Precats are small and are designed to slightly reduce emissions as they are closer to the heat to warm up faster.

The main cats then finish the job. Today's high flow cats have very little impact on performance. If you want a car that don't stink up the gauge I'd do a full Magnaflow replacement if your car came with cats.

 

Sorry, my car is an 89 TPI. It's stock except for a catless magnaflow exhaust. I just hate the smell in general. It's exactly what DanielRicany is describing. Id rather have a little less performance if I can have less exhaust smell. So my question is, can I stop the smell with precats or is there no point and just go with a high flow cat? Its more of a Cat vs Precat question.

 

idle smell can be unbelievably frustrating.

ive fought idle smell ever on my batch fire speed density 93 ever since cat removal and hotcam install (done at same time).

IMHO the cats are a band aid fix for batch fire problems .

dont let anyone tell you that you can tune it out by ve table modifications.

you can get open loop (cold ) idle solved, but when it warms up it goes into closed loop and the garbage smell comes back.

the problem with a cam is anything bigger than stock has overlap (intake and exhaust open at same time for brief period). during this phase any unburned oxygen goes into the exhaust and makes your o2 sensor see a 'lean' condition causing it to dump fuel.

once you are driving and rpms are up, no big deal you dont seem to get it.

its a nasty smell that sticks to your clothes. my wife used to smell it and say 'oh, you drove the vette today'. in my case it was not necessarily a raw gas smell but something in between.

ive had some success with idle smell by going to open loop idle below 1200 rpm. some of it is still there.

i recently saw a c4 with a 250 ish duration intake cam (ie, big cam) and it had the c4 fuel inj replaced with holley fuel inj.

to my surprise, it didnt smell much at all at idle. i wonder if holley fuel inj is a sequential system (vs batch fire)......that said i didnt ask the owner if he had cats on it. i suspect he didnt as this was a rural county in michigan

 

I know for a fact your $6E ECM can be tuned out!! I only sampled & burned a few tables within the 92 - 93 speed density system. I do know the 94 -95 sequential system the "only" way to solve the AFR @ Idle. is in fact. the minimum & maximum BLM constant tables. needs a tighter window.

94 OE
Min was 108 VS my current 113
Max was 160 VS my current 142

to keep alive
Min 120 VS my current 132
Max 160 VS my current 140

my previous CC306 built $6E ~ ECM. Holley Stealth Ram. NO cats. smelled awesome at start & idle. My current EE ~ PCM. NO cats. smells awesome at start & idle.

 

Put the cats on your smell should go away
All cars without one will stink a little even stock ones

 

If you really want those precats I have the front factory OEM Y-pipe with precats from my '89 hanging in my garage. PM me I'm local to NYC as well!