Catalytic converter and emissions?

[maybeadinosaur]

Hey everyone,
PO removed the cat and emissions set up under the hood. My muffler was rusted out so I had it replaced but passed on a new cat, at the time, because of the cost. Now after a few years and a toddler around, we’re getting a little tired of the smell now and, while there’s a chance of a minor exhaust leak somewhere, I’m wondering if it’s worth getting a cat (and possibly have the emissions gear put back in).

I’m also not one for the loud rumble so I’m curious if it will help a little with sound.

What do you all think?

[wiley-moeracing]

Put a cat on, and make sure the exhaust is run all the way out back and all joints are welded or clamped correctly. A good muffler will help with your noise also.

[babywag]

Yes! A CAT will reduce both stink and noise.
If you don't weld or have access to one exhaust band clamps are the way to go for installing one. Save the labor $$ vs. a shop doing it for you.

The missing emissions equipment won't do anything for noise or smell.
Fine tuning will also reduce stink, what most folks don't get about emissions is it is primarily for complete combustion which reduces noxious gases/odors.
A poorly tuned engine will stink worse than one tuned for emissions.

[maybeadinosaur]

Thanks for affirming what I thought. I know it adds pressure to the system and slightly slows exhaust but I can only imagine it is minor

I cant DIY this so Ill call around for pricing

[61Hawk]

I just did this on my '89. I removed the air pump and all of the crap under the hood because the air pump locked up for the second time within three years. While I was replacing the muffler I cut off the air tube going to the catalytic converter and folded it over, then realized I should probably replace it with a a modern one. Put it on two weeks ago and between that and replacing the choke pull off I can now stand behind my GW and not tear up like I'm in a gas chamber. The only thing that make me pull away from sniffing the exhaust (seeing how much of a gas smell I could smell) was the heat, I couldn't smell anything. My old catalytic converter was completely gutted, I thought I was going to be able to make a little money off it but it was nothing but scrap metal.


If you're going to do it yourself, pull the muffler off, cut the catalytic converter off where it joins the down pipe (you're not going to beat the two apart), separate the remaining catalytic converter tube from the downpipe with a screwdriver wedged between the two of them. It's nothing I enjoyed doing, but the end results were worth it.

[DarkMonohue]

I know it adds pressure to the system and slightly slows exhaust but I can only imagine it

Thankfully, that hasn't really been true for a long time now. It's one of those persistent old rumors that gets repeated until everybody "knows" it must be true, despite being entirely bogus.

Old catalytic converters were, admittedly, notoriously restrictive. Modern cats add so little backpressure that it just isn't worth worrying about. You will not experience any measurable power loss by adding a modern cat. Exhaust noise will also be reduced a little.

[maybeadinosaur]

Well, I called my local muffler shop and they guy was very helpful. He recommended looking at the carb and vacuum first, saying the cat probably wouldn’t fix the smell, but could instead make it worse by heating up the (Possibly rich) exhaust.

My carb was rebuilt about 5k miles ago but hasn’t been tuned up since. Thinking I should start there...but I still want to get the noise down a little, too.

[SJTD]

Thankfully, that hasn't really been true for a long time now. It's one of those persistent old rumors that gets repeated until everybody "knows" it must be true, despite being entirely bogus.

Old catalytic converters were, admittedly, notoriously restrictive. Modern cats add so little backpressure that it just isn't worth worrying about. You will not experience any measurable power loss by adding a modern cat. Exhaust noise will also be reduced a little.

Wait, what? Everyone knows back pressure is good for torque so wouldn't and older cat be better?

[SJTD]

What what causes the smell? Incomplete combustion.

What do cats do. Oxidize the unburned HC's that stink.

Why wouldn't it help the smell?

[babywag]

lol...
a cat definitely reduces stank.
my youngest HATES exhaust smell.
She noticed reduced stank immediately after a new CAT was required on my 90 to pass smog.
I didn't notice difference but she did right away.

[DarkMonohue]

Wait, what? Everyone knows back pressure is good for torque so wouldn't and older cat be better?

Yep. Pro tip: for heavy towing, shove a few pounds of russet potatoes into your tailpipe. Torque production will go through the roof! Plus, when you arrive at your destination, you'll have a tasty snack, hot and ready for the whole family to enjoy.

[babywag]

Yep. Pro tip: for heavy towing, shove a few pounds of russet potatoes into your tailpipe. Torque production will go through the roof! Plus, when you arrive at your destination, you'll have a tasty snack, hot and ready for the whole family to enjoy.

I prefer to use burritos

[SJTD]

Tailpipe taters?

[61Hawk]

Some people prefer to use expanding foam.

https://www.carscoops.com/2020/05/angry-neighbor-allegedly-uses-expanding-foam-to-silence-mustangs-noisy-exhaust/