Cats on TTI exhaust system

[junkyardhero]

not the answer i was expecting, but interesting none the less.

and, like interesting in a tin foil hat kinds of interesting.

throw a tune up on and roll, they run surprisingly clean for what they are. or spend a bajillion dollars on EFI and stuff and never, ever get that money back out if you sell it.

 

[jos51700]

I've considered running catalytic converters on my Magnum Dart. I like quiet and there's nothing wrong with clean if it doesn't hurt performance

 

[harrisonm]

I watched a documentary on the environmental effects of emissions on shellfish. Also would like to warm it up without stinking up my driveway.

Look, nothing personal, but there are documentaries on all kinds of things; the pyramids were built by aliens, the world trade centers were brought down by Bush, the glaciers are all going to melt and we'll all be underwater. If you want to put cats on your car to make your it cleaner, then good for you. I applaud that. But don't do it because of a documentary on shellfish. I have watched a lot of shady documentaries. My favorites are the ones that say we'll all be dead in 10 years due to climate change. In the last 30 years, those warning deadlines have come and gone several times. Each time there was a TV show about it showing all the non-arguable data. Modern high performance cars have to work around the Cats with other performance items.

 

[remytherat]

the pyramids were built by aliens

I've been wrapping my balls in tin foil every day for no reason??????


Someone needs to put out a public statement on these shady documentaries

 

[Garrett Ellison]

Why? What is wrong with wanting cats on an old car? New cars with higher performance engines run cats.

Because there’s a lot more to it than h just adding cats to the exhaust system. You’ll need to collect data on your present emissions output and then you’d have to establish a realistic target to reduce emissions to. Then you’ll get into an EGR circuit carburetor, unless you’re converting to a “real” EFI system with plenty of inputs and outputs to control that sort of thing. Although EGR isn’t required to use cats, it does help reduce the amount of CO they have to convert to CO2 by reducing fuel the engine needs to run, but it needs a metric crap ton of timing when the EGR is running. EGR also reduces NOX emissions by reducing combustion chamber temperatures. And then you’re probably going to looking at exhaust air injection to give the cats some oxygen to convert the CO to CO2. Then have everything sized properly for the catalytic converters to maintain operating temperature. I can’t imagine 3 inch dual high flow cats doing a whole lot of anything on a 360 as far as emissions reduction goes. The other question is, how stock or non stock is the engine and how performance oriented is it?

 

[Garrett Ellison]

I've been wrapping my balls in tin foil every day for no reason??????

 

[harrisonm]

I've been wrapping my balls in tin foil every day for no reason??????


Someone needs to put out a public statement on these shady documentaries

Dude, don't you know the tin foil goes on your head?????
That's where I wear mine.

 

[remytherat]

Dude, don't you know the tin foil goes on your head?????

Given how I tend to make decisions, I'm pretty sure my brain is actually down there.

 

[n00blike]

not the answer i was expecting, but interesting none the less.

and, like interesting in a tin foil hat kinds of interesting.

throw a tune up on and roll, they run surprisingly clean for what they are. or spend a bajillion dollars on EFI and stuff and never, ever get that money back out if you sell it.

Currently the exhaust is in need of repair so I was wanting to get that out of the way. I was thinking of going EFI eventually, but still want to upgrade the cam and cylinder heads. I guess I'll revisit this when I go it EFI.

 

[n00blike]

Found a good explanation from Chat GPT:

The Technical Challenge
Catalytic converters are extremely sensitive to the Air/Fuel ratio.
If the engine runs too rich (too much fuel): Unburnt raw fuel enters the converter. When it hits the hot internal structure, it can ignite, causing a "meltdown" that destroys the converter.
If the engine runs too lean (too much air): The chemical reactions stall, and the converter stops cleaning the exhaust.

Catalytic converters work best at the Stoichiometric Ratio, which for pure gasoline is 14.7:1 (14.7 parts air to 1 part fuel).
In engineering terms, this specific point is often referred to as Lambda 1.0 (\lambda = 1.0).

The "efficiency window" for a three-way catalytic converter is incredibly narrow. It sits between 0.995 and 1.005 Lambda.


It would be interesting to data log AFR.

While the engine can theoretically run safely between 0.85 (Rich) and 1.15 (Lean), the catalytic converter acts like a "chemical gatekeeper" that only opens fully when the engine is right at 1.0.

Note on Modern Fuels
While 14.7:1 is the standard number for pure gasoline, most modern pump gas contains 10% Ethanol (E10). Ethanol requires more fuel to burn, so the perfect ratio for E10 gas is actually slightly lower, around 14.1:1.
However, because modern cars use oxygen sensors that target "Lambda 1.0" (complete combustion) rather than a specific weight of fuel, they automatically adjust to this difference without you noticing.

 

[plymouth4onthefloor]

Nothing wrong with a catalytic converter, automotive standard is 300 cell. must be big enough for the power. heat insulating to the floor necessary! Put the cat as much forward you can for fast heating up. Run it with Efi and a professionall tune. This will be a high dollar invest. You have to run it rich 0.85 under high load to prefent cats from melting. A good cat will kill almost no power.

 

[ir3333]

I've actually wondered about this. If it can make a difference it's probably a good idea. It's brutal being in the last half to leave cruz night or even be near an old muscle car that is just idling.

 

[Professor Fate]

What they convert

A catalytic converter turns:

• Carbon monoxide (CO) → carbon dioxide (CO₂)
• Unburned hydrocarbons (HC) → water (H₂O) + CO₂
• Nitrogen oxides (NOx) → nitrogen (N₂) + oxygen (O₂)

Yes — nitrogen oxides (NOx) can indirectly harm shellfish, though the effect isn’t usually direct poisoning. The main issue is how NOx changes the chemistry of the water.


Here’s how it works:

1. NOx contributes to ocean acidification​

NOx released into the air (from cars, power plants, agriculture) can dissolve into rainwater and form nitric acid.
When this enters the ocean or coastal waters, it lowers pH slightly, contributing to acidification.

Why this harms shellfish​

Shellfish such as oysters, clams, mussels, and scallops need carbonate ions to build their calcium carbonate shells.
Acidification reduces carbonate availability, making it:

• harder for juveniles to form shells
• easier for existing shells to dissolve
• more energy-intensive to grow

This leads to lower survival and slower growth, especially in larvae.

2. NOx can also cause nutrient pollution​

Nitrogen compounds that settle from air pollution can act like fertilizer in coastal waters.
This can trigger algal blooms, which:

• reduce water clarity
• deplete oxygen when algae die and decay
• create “dead zones” where shellfish can’t survive

Oxygen depletion (hypoxia) is extremely stressful or fatal to shellfish.

3. Direct toxicity is minimal​

NOx doesn’t typically reach concentrations in water that would directly poison shellfish. The harm is mostly through acidification and eutrophication.

You missed a couple important factors.
Fuel contains hydrogen sulfides.
A correctly functioning catalytic convertor converts these hydrogen sulfides into sulfur dioxide (SO2).
Sulfur dioxide reacts with moisture to create sulfurous acid (H2SO3), then oxidizes in the atmosphere into sulfur trioxide (SO3). This further reacts with water to create H2SO4- sulfuric acid. This is the major cause of acid rain, and acidification of the environment.
The takeaway?
Catalytic convertors themselves are killing the environment.
Politicians (EPA) arbitrarily came up with a short list of pollutants (carbon monoxide, hydrocarbons, and nitrogen oxides) and mandated the use of catalytic convertors to convert those three pollutants into "less harmful" (re: non-regulated) compounds.
The incidental creation and introduction of sulfuric acid (and other chemicals) into our environment through the use of cats is something that has long been downplayed, since that would call into question the wisdom of our politicians (pretending to be engineers) who mandated this...
Not to mention the social and environmental impact of mining/processing/refining the platinum, palladium, and rhodium required for the manufacture of catalytic convertors... but that is a whole other discussion.
Follow the science, not the "We're all gonna die/humans are evil/donate today" docudramas.
Humans aren't evil, but we can be pretty stupid at times and be our own worst enemies.

 

[Garrett Ellison]

Trying to cure the evils of air pollution with automobiles is a moot point if you start looking at pollution caused by the use of bunker fuel in the global shipping industry. I’m surprised there hasn’t been more push forwards nuclear propulsion on that industry like is seen in the Merchant Marines and Naval fleets of the world. Some sources report that the sulfurous output of global shipping is four times greater than all the cars on earth.

 

[go-fish]

@n00blike

It sounds like you're on the right track. You have figured out that you need your engine to be tuned right whether you do EFI or carburetor. To achieve this with a carb you will need an appropriate carb that is tuned well and having this knowledge is key. User will need to periodically maintain and change(schedule depends on factors) parts of the carburetor. Other hardware: Vacuum gauge, Lamda gauge, A/F ratio gauge and O2 sensor. You will need to translate all the data and tune it. You can even get into data logging for a substantial price; it's not needed nor typical. At this point you could get the engine to have as much control that you could get from a carbureted system, emissions wise and power/economy wise. This is your carbureted route
If you commit to the carburetor route you will be almost required to be hands on. There are pros to having carburetor knowledge. I'm going through it now on a numbers matching Duster 340 4-speed daily driver. Thought I wanted EFI but decided to commit to the carb and buy the hardware I listed above along with a few books and YT channel subs. Saving money, gaining knowledge, and keeping it more traditional. I want to add these gauges and tune to peak efficiency. I don't care to run cats at the moment but I do appreciate your concern.
EFI solves a lot of the user's responsibility after it's tuned properly, provides the necessary sensors, and you can even get a system that provides datalogging. You'll end up paying more for a new fuel system entirely so add in tank, pump, lines, filters, fittings, and the EFI system itself. Different cam and definitely an overdrive would be best for you so how far do you want to go?
I'll consider it more so for sound reduction, fuel smell, and packaging in the future. Potentially, 3" Boomtube side exit with a resonator and high flow 4" OD cats on a different car that would use Holley Terminator X. (Exhaust Inspiration: Cam Racing but maybe with an H-pipe.) Good to know I will, if even in an infinitesimal way, be helping ocean life. I jest, but it's not to say I disregard the environment and I wouldn't delete the catalytic system (upgrade?) on cars that came with them. A well tuned automobile is best for every owner. IF you have it in your heart and you're called to do this with a passion then you would would want to know all the data. Fuel system style needs the data to be interpreted. In the end you are the one determining the logic and decision making in a carbureted system whereas EFI is doing it right up to AI integration in /OEMs. Carb is more hands-on. EFI can be tuned and (if you're lucky) be forgotten or you can tune infinitely with knowledge and data.
What's in your wheelhouse and what's in your budget?
If this was my mission (Shellfish) I would be looking at an EV swap, but then you're ignoring battery pollution, and you know, the African kids over in the mines. If you're getting power from especially coal then disregard.

 

[remytherat]

A correctly functioning catalytic convertor converts these hydrogen sulfides into sulfur dioxide (SO2).

There is almost no sulfur is modern gasoline

pollution caused by the use of bunker fuel in the global shipping industry.

I was about to say, go drive down to the port of long beach and learn where LA smog really comes from. Oil refineries, ships burning bunker oil, many thousands of trucks….

 

[n00blike]

You missed a couple important factors.
Fuel contains hydrogen sulfides.
A correctly functioning catalytic convertor converts these hydrogen sulfides into sulfur dioxide (SO2).
Sulfur dioxide reacts with moisture to create sulfurous acid (H2SO3), then oxidizes in the atmosphere into sulfur trioxide (SO3). This further reacts with water to create H2SO4- sulfuric acid. This is the major cause of acid rain, and acidification of the environment.
The takeaway?
Catalytic convertors themselves are killing the environment.
Politicians (EPA) arbitrarily came up with a short list of pollutants (carbon monoxide, hydrocarbons, and nitrogen oxides) and mandated the use of catalytic convertors to convert those three pollutants into "less harmful" (re: non-regulated) compounds.
The incidental creation and introduction of sulfuric acid (and other chemicals) into our environment through the use of cats is something that has long been downplayed, since that would call into question the wisdom of our politicians (pretending to be engineers) who mandated this...
Not to mention the social and environmental impact of mining/processing/refining the platinum, palladium, and rhodium required for the manufacture of catalytic convertors... but that is a whole other discussion.
Follow the science, not the "We're all gonna die/humans are evil/donate today" docudramas.
Humans aren't evil, but we can be pretty stupid at times and be our own worst enemies.

Interesting, I didn't know about that. Thanks for the info!

 

[RustyRatRod]

You missed a couple important factors.
Fuel contains hydrogen sulfides.
A correctly functioning catalytic convertor converts these hydrogen sulfides into sulfur dioxide (SO2).
Sulfur dioxide reacts with moisture to create sulfurous acid (H2SO3), then oxidizes in the atmosphere into sulfur trioxide (SO3). This further reacts with water to create H2SO4- sulfuric acid. This is the major cause of acid rain, and acidification of the environment.
The takeaway?
Catalytic convertors themselves are killing the environment.
Politicians (EPA) arbitrarily came up with a short list of pollutants (carbon monoxide, hydrocarbons, and nitrogen oxides) and mandated the use of catalytic convertors to convert those three pollutants into "less harmful" (re: non-regulated) compounds.
The incidental creation and introduction of sulfuric acid (and other chemicals) into our environment through the use of cats is something that has long been downplayed, since that would call into question the wisdom of our politicians (pretending to be engineers) who mandated this...
Not to mention the social and environmental impact of mining/processing/refining the platinum, palladium, and rhodium required for the manufacture of catalytic convertors... but that is a whole other discussion.
Follow the science, not the "We're all gonna die/humans are evil/donate today" docudramas.
Humans aren't evil, but we can be pretty stupid at times and be our own worst enemies.

And therein once again is proof that whatever government touches, it destroys.

 

[RustyRatRod]

There is almost no sulfur is modern gasoline

Almost none, means a little bit. Times how many hundreds of millions of gas burning engines around the whole world. But wait a minute. The whole world does not adhere to the strict requirements for gasoline that the US does so lots of countries have more than "a little bit".

 

[n00blike]

@n00blike

It sounds like you're on the right track. You have figured out that you need your engine to be tuned right whether you do EFI or carburetor. To achieve this with a carb you will need an appropriate carb that is tuned well and having this knowledge is key. User will need to periodically maintain and change(schedule depends on factors) parts of the carburetor. Other hardware: Vacuum gauge, Lamda gauge, A/F ratio gauge and O2 sensor. You will need to translate all the data and tune it. You can even get into data logging for a substantial price; it's not needed nor typical. At this point you could get the engine to have as much control that you could get from a carbureted system, emissions wise and power/economy wise. This is your carbureted route
If you commit to the carburetor route you will be almost required to be hands on. There are pros to having carburetor knowledge. I'm going through it now on a numbers matching Duster 340 4-speed daily driver. Thought I wanted EFI but decided to commit to the carb and buy the hardware I listed above along with a few books and YT channel subs. Saving money, gaining knowledge, and keeping it more traditional. I want to add these gauges and tune to peak efficiency. I don't care to run cats at the moment but I do appreciate your concern.
EFI solves a lot of the user's responsibility after it's tuned properly, provides the necessary sensors, and you can even get a system that provides datalogging. You'll end up paying more for a new fuel system entirely so add in tank, pump, lines, filters, fittings, and the EFI system itself. Different cam and definitely an overdrive would be best for you so how far do you want to go?
I'll consider it more so for sound reduction, fuel smell, and packaging in the future. Potentially, 3" Boomtube side exit with a resonator and high flow 4" OD cats on a different car that would use Holley Terminator X. (Exhaust Inspiration: Cam Racing but maybe with an H-pipe.) Good to know I will, if even in an infinitesimal way, be helping ocean life. I jest, but it's not to say I disregard the environment and I wouldn't delete the catalytic system (upgrade?) on cars that came with them. A well tuned automobile is best for every owner. IF you have it in your heart and you're called to do this with a passion then you would would want to know all the data. Fuel system style needs the data to be interpreted. In the end you are the one determining the logic and decision making in a carbureted system whereas EFI is doing it right up to AI integration in /OEMs. Carb is more hands-on. EFI can be tuned and (if you're lucky) be forgotten or you can tune infinitely with knowledge and data.
What's in your wheelhouse and what's in your budget?
If this was my mission (Shellfish) I would be looking at an EV swap, but then you're ignoring battery pollution, and you know, the African kids over in the mines. If you're getting power from especially coal then disregard.

I'm in the point of my life were I have the budget to spend on my hobbies and come from a mechanical engineering background so I don't mind learning and tweaking with things. It's going to be a long learning processes as I'm not in a rush, my hobbies are more about learning and implementing my knowledge.

I recently saw some videos where David Freiburger spent a long time tuning the carb on his Duster. It surprised me how much tinkering he had to do with how long he has been working on older cars. This is making me lean to EFI.

My main mission it to enjoy my duster while being environmentally responsible. Simple things like taking used oil to the collection station and not dumping it down the drain.

 

[RustyRatRod]

I'm in the point of my life were I have the budget to spend on my hobbies and come from a mechanical engineering background so I don't mind learning and tweaking with things. It's going to be a long learning processes as I'm not in a rush, my hobbies are more about learning and implementing my knowledge.

I recently saw some videos where David Freiburger spent a long time tuning the carb on his Duster. It surprised me how much tinkering he had to do with how long he has been working on older cars. This is making me lean to EFI.

My main mission it to enjoy my duster while being environmentally responsible. Simple things like taking used oil to the collection station and not dumping it down the drain.

Hey look, build your car how you want it. We're just spoutin off what we'd do if it was our car. It's your money and your car. If you wanna weld cats all over the exterior, go for it. Do what makes you happy with it.

 

[mopowers]

You missed a couple important factors.
Fuel contains hydrogen sulfides.
A correctly functioning catalytic convertor converts these hydrogen sulfides into sulfur dioxide (SO2).
Sulfur dioxide reacts with moisture to create sulfurous acid (H2SO3), then oxidizes in the atmosphere into sulfur trioxide (SO3). This further reacts with water to create H2SO4- sulfuric acid. This is the major cause of acid rain, and acidification of the environment.
The takeaway?
Catalytic convertors themselves are killing the environment.
Politicians (EPA) arbitrarily came up with a short list of pollutants (carbon monoxide, hydrocarbons, and nitrogen oxides) and mandated the use of catalytic convertors to convert those three pollutants into "less harmful" (re: non-regulated) compounds.
The incidental creation and introduction of sulfuric acid (and other chemicals) into our environment through the use of cats is something that has long been downplayed, since that would call into question the wisdom of our politicians (pretending to be engineers) who mandated this...
Not to mention the social and environmental impact of mining/processing/refining the platinum, palladium, and rhodium required for the manufacture of catalytic convertors... but that is a whole other discussion.
Follow the science, not the "We're all gonna die/humans are evil/donate today" docudramas.
Humans aren't evil, but we can be pretty stupid at times and be our own worst enemies.

There's some truth to this, but there's also quite a bit of misinformation in this one.

 

[junkyardhero]

if this is for your own satisfaction to say: i did that, well, fine.

however if this is about pollution or reducing a carbon footprint then you'd be better off and enact more change by getting yourself a bicycle, buying less from amazon with all the petroleum based packaging and lobbying local government for better mass transit.

but if you gotta have a car, then why not convert it to run on LPG or CNG?

also, don't delude yourself into thinking that "EFI is easier than a carb"; it comes with its own set of problems, pitfalls and learning curve.

 

[go-fish]

I'm in the point of my life were I have the budget to spend on my hobbies and come from a mechanical engineering background so I don't mind learning and tweaking with things. It's going to be a long learning processes as I'm not in a rush, my hobbies are more about learning and implementing my knowledge.

I recently saw some videos where David Freiburger spent a long time tuning the carb on his Duster. It surprised me how much tinkering he had to do with how long he has been working on older cars. This is making me lean to EFI.

My main mission it to enjoy my duster while being environmentally responsible. Simple things like taking used oil to the collection station and not dumping it down the drain.

First, who do you know pouring oil down the drain? Damn.

I would say if you really want to dig into it, learn where the data comes from, how to tune for it, like to see improvements over time, then a carburetor is for you.
If you want to really dig into efi and learn to tune and see improvements over time you can do that. Both, changing tune as need be.
If you want to hit the easy button, get the efi (or carb) and have a pro install and tune it to your application. Take it back to them if you ever need.

One thing we didn't discuss was how far could you be away from home. EVEN IF you learn your EFI to a gnats *** you could break down and be waiting for days on replacement parts. Roadtrip sound good? With a carb you could get any repair parts you need in almost any town. Dave Freiberger just switched to the Slayer 600 vacuum secondary carb like I am using. I want to drive my Duster like he does, I just need a GV for road trips. I was on the fence with the carb/EFI and then my dad had the problem with Holley Sniper. What would DF do? Well, he went to the carb I already have. Since I wanted all the things EFI gives you I decided to get the gauges I needed for the data I need to tune a carb properly.
My only thing against EFI is the getting stranded thing. I would just want to be able to be run back to the house to grab my truck and trailer. My prospective EFI car would not go on overnighters without being trailered. Think race car.
With the carb, A/F ratio gauge and O2 sensor, vacuum, and tach you will be able to run as clean as EFI in most every situation. Learning the tuning and equipment better is going to be required in both cases.

 

[chryslercruiser]

Hello, I have a 74 Duster with a 360 and TTI headers. I'm looking to get the TTI exhaust system, but I would like to add catalytic converts. Does anyone have experience running the TTI 3" exhaust system with catalytic converters? How was the fitment?

This is a fine question, and well worth asking...

Cats and carbs dont get a long real well.

I suspect most of the dismissive answers are due to the above fact... carbs are not good at keeping the AFR in the range that a converter will tolerate for long..

EFI would work better... which is why performance came back after the big three and everyone figured out EFI...

If you want to do it on a budget, get yourself a 96-ish 2 wheel drive Ram truck w/ a 5.9 magnum, and swap engine and transmission.. and computers.. it's been done before, and you can benefit from the factory efforts.. drivability will be a whole lot better than with a carb...

OR you can go the aftermarket route, but that seems to be the difficult path, unless you want some power adder later... which the factory EFI won't be very easily tuned to accept..

Whatever your decision, it is a fine question to ask, even if most don't understand or accept the "why" behind the question.

This seems to be a thoughtful discussion on the topic: Anyone run high-flow Cats to reduce hydrocarbon exhaust smell?