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Catalytic converts with sniper EFI? Due to health related problems

mouserider

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Alright, I have seen few threads people were asking about cats for pollution reduction and threads was always going into “you don’t need it, it’s not that bad” . I personally agree , i don’t care as well, but, since I was kid, I have those migraines, I can’t wear caps, neither glasses, any head pressure or fumes and i will have a headache for a whole day. Since I got my charger , every ride is a full day headache, even though I enjoy driving it, I noticed that I pick another car.

For the last 5 years I have been trying to minimize it, completely rebuilt my exhaust system, went efi, checked every damn hole and rubber plug. There is almost no fumes when I’m driving it, but at traffic lights or in traffic it gets in, my clothes always smell and my head is blowing. Any other wouldn’t notice that, but i do.

I have another car jag xjs v12 , it has 2 cats which are almost gone, and still it’s enough for me not to get a headache and enjoy driving it.

My charger 1971 383 is in perfect shape , engine singing, efi does it job, ignition controlled by efi.

So, question is, what cats should I get and what other things I should know or do before that.
 
I’m not sure exactly, but I do know that “hi flow” cats are high flow because there aren’t much guts in them & often they don’t really work. If it were me, I’d measure under the car to see what kind of room I have to work with. Then, look for any type of OEM-style replacement cat, as large as possible, that fit the space I had to work with. Also, you need to match the exhaust diameter and an in/out on the cats that’s easy to weld into your exhaust system. Think of them as “extra custom mufflers”
 
Even with cats you will still get some until you fix why it is getting in the car. And if really think your car is the problem how about all the cars, trucks, and cycles that are sitting at the stop sign with you. You should be smelling them long before yours.
 
First, I'd try to verify what is causing your issues. Maybe it is just a rich fuel mixture? The Sniper EFI should have controlled this, but my EFI system has different settings for air/fuel ratio. Do you still have a rich idle A/F ratio? Maybe something to check.

A catalytic converter converts CO, NOx and HC to CO2, H2O and N2. So if lack of these is causing you issues, that means you are reacting to CO, NOx or HC. I'm not sure if there is a way to test this before spending time and money to add catalytic converters?

Having said the above, I am not aware of any issues with adding them other than finding an appropriate space to mount them. I don't have any experience with one catalytic converter over another, so I can't help you there.
 
Try installing a new trunk lid gasket.
I'm betting it seals poorly.
 
Alright, I have seen few threads people were asking about cats for pollution reduction and threads was always going into “you don’t need it, it’s not that bad” . I personally agree , i don’t care as well, but, since I was kid, I have those migraines, I can’t wear caps, neither glasses, any head pressure or fumes and i will have a headache for a whole day. Since I got my charger , every ride is a full day headache, even though I enjoy driving it, I noticed that I pick another car.

For the last 5 years I have been trying to minimize it, completely rebuilt my exhaust system, went efi, checked every damn hole and rubber plug. There is almost no fumes when I’m driving it, but at traffic lights or in traffic it gets in, my clothes always smell and my head is blowing. Any other wouldn’t notice that, but i do.

I have another car jag xjs v12 , it has 2 cats which are almost gone, and still it’s enough for me not to get a headache and enjoy driving it.

My charger 1971 383 is in perfect shape , engine singing, efi does it job, ignition controlled by efi.

So, question is, what cats should I get and what other things I should know or do before that.
I investigated adding cats to my 72 Road Runner but since my car is 25,000 miles and never restored I decided to go with an Accurate exhaust which is pretty close to original. So a couple of thoughts: cats work best when they are closest to the exhaust manifold. They need to get as hot as possible. So therefore you will need heat shielding. You should look at the service manuals for the 1975 B-Body cars to see where Chrysler put the cats and how much shielding they used. Not as efficient, but maybe easier to do would be to just swap the resonators for the cats. If your car has resonators. I can't find my notes but I did talk to several aftermarket exhaust companies and I think Flowmaster was the one that was quite helpful. They had cats for 72 Road Runner both in California spec and 49State spec. So I imagine you would want CA spec. With adding the cats you will increase back pressure so that is a question to ask. You might be able to offset that increase with less restrictive muffler and/or resonator deletes. But you should give a few of the muffler/exhasut companies a call and see what they say. Like I said, I came close but decided to try to stay as original as possible. Good luck!
 
First, I'd try to verify what is causing your issues. Maybe it is just a rich fuel mixture? The Sniper EFI should have controlled this, but my EFI system has different settings for air/fuel ratio. Do you still have a rich idle A/F ratio? Maybe something to check.

A catalytic converter converts CO, NOx and HC to CO2, H2O and N2. So if lack of these is causing you issues, that means you are reacting to CO, NOx or HC. I'm not sure if there is a way to test this before spending time and money to add catalytic converters?

Having said the above, I am not aware of any issues with adding them other than finding an appropriate space to mount them. I don't have any experience with one catalytic converter over another, so I can't help you there.
Thanks for tips! I don’t know what I’m reacting to, I can smell petrol all day while working on fuel delivery, and all good, I have jag v12 5.3 and it does smell differently and doesnt really annoy me. But charger smells exactly like my father’s car from childhood, and it kills me in a second. The difference is only cats I assume.

AFR is good, and I have same problem as it was with carbs , then other carbs, then EFI.

Yes, mb some fumes are getting inside, i tried to find all possible leaks, but you never know with project car, exhaust is custom, body was completely restored, something could definitely went differently then oem and it’s pain to find.
 
Try installing a new trunk lid gasket.
I'm betting it seals poorly.
Done, every single rubber component is new, I even put clothes in trunk covering entire floor to check later if it smells . As I said , when car is in park and you are in traffic with windows down and wind is blowing from behind how seals can fix that.
 
Done, every single rubber component is new, I even put clothes in trunk covering entire floor to check later if it smells . As I said , when car is in park and you are in traffic with windows down and wind is blowing from behind how seals can fix that.
Get an electric car. Then you will only smell the other billion on the road.
 
Disclaimer: I do not have EFI of any type on any old car.

From reading, engine masters, other various you tube channels, it seems to me that a carburetor replacement EFI like a Holley sniper is still subject to the same problems as a carburetor. Meaning dual plane, big overlap cam, wrong ignition timing, poor vacuum signal, all contribute to a poor running engine, period.
A EFI system can clean up air fuel ratios quite a bit and fairly quickly. However it cannot undo the laws of physics. A dual plane with all its twist and turns still knocks fuel out of suspension causing it to pool in certain areas of the manifold cause rich and lean conditions in different cylinders and even more poor vacuum signal which EFI absolutely hates, mostly because it tries to correct and snowballs out of control. These issues go on and on. Your catalytic converter "solution" may or may not work, because a catalytic converter has to reach a minimum temperature to "light off", think of it as a little furnace that cooks the exhaust gases while exposed to the metals(catalyst) to convert their molecules to other molecules of less toxicity.
Without getting more long winded, a cat only works when high temperature is maintained, in other words a lean type 13.8-14.7 range or so air fuel ratio. Real world meaning. Even the newest cars cats go into bypass (can't keep up) at WOT ~12.5-13.2 afr, this is accepted because how long is a engine at WOT over the 100k+ miles that a cat last. Problem is if idle afr is crappy, smelling rich burning your eyes etc. the cat will not convert the poisonous gases to less poisonous gases because it loses its range of heat. Worse yet is when you start driving (after a longer idling period) the cat overheats damaging the inner structure and premature failure. I don't know if this helps you any, but a cat is a expensive thing to damage because of problems it is not designed to fix.
Basically it is designed to clean up the exhaust on a properly running engine under most conditions. It's a band aid to keep a cut clean, not stop arterial bleeding. Not saying it will not fix your problem (headache), that sounds like would not bother most of us (no headache).
Good luck.
 
Done, every single rubber component is new, I even put clothes in trunk covering entire floor to check later if it smells . As I said , when car is in park and you are in traffic with windows down and wind is blowing from behind how seals can fix that.
Ok well there was no way I would know that
 
First, I'd try to verify what is causing your issues. Maybe it is just a rich fuel mixture? The Sniper EFI should have controlled this, but my EFI system has different settings for air/fuel ratio. Do you still have a rich idle A/F ratio? Maybe something to check.

A catalytic converter converts CO, NOx and HC to CO2, H2O and N2. So if lack of these is causing you issues, that means you are reacting to CO, NOx or HC. I'm not sure if there is a way to test this before spending time and money to add catalytic converters?

Having said the above, I am not aware of any issues with adding them other than finding an appropriate space to mount them. I don't have any experience with one catalytic converter over another, so I can't help you there.
Based on my experience with my 95 Dakota, a cat doesn't touch NOx.....at least it didn't on mine. Failed NOx so went and got a new cat put on under warranty and still had just as high of a number. However I did find out after some research that a cooler engine reduced it and so did a new air filter and no air filter was even better! A good EGR system will also help and that's probably what it needed the most but wasn't going to dig into that. I finally got my inspection date in the dead of winter and that helped a lot. Don't know about todays cats but this was my experience with the older ones. Now that the truck is well past 25, I don't have to get it emissions tested anymore and I'm a happy camper :)
 
Fuel quality, blends, and octane all make a difference.
 
I changed my mind. These guys are right that the cats need to be as close to the engine as possible so they get hot. The factory ‘75 b-body cat would be a great place to start looking.
 
You guys are all spot on , even though you have a new trunk seal , double check it! Cats must and will get hot , shield well. Engine tune is important. Good Luck!
 
I am not aware of any issues with adding them other than finding an appropriate space to mount them.
So I think I have to say I was wrong here. It seems like catalytic converters like heat to operate, so it seems location might matter a lot.

Based on my experience with my 95 Dakota, a cat doesn't touch NOx.....at least it didn't on mine. Failed NOx so went and got a new cat put on under warranty and still had just as high of a number. However I did find out after some research that a cooler engine reduced it and so did a new air filter and no air filter was even better! A good EGR system will also help and that's probably what it needed the most but wasn't going to dig into that. I finally got my inspection date in the dead of winter and that helped a lot. Don't know about todays cats but this was my experience with the older ones. Now that the truck is well past 25, I don't have to get it emissions tested anymore and I'm a happy camper :)
I decided to look it up, since I obviously do not have a good grasp on catalytic converter details. It seems there are two kinds of converters.

Per a UTI article (What Is a Catalytic Converter and What Does It Do? | UTI): "There are two main types of catalysts that might be featured in a car:
  • Reduction catalysts: Help reduce nitrogen oxide pollution by removing oxygen. Nitrogen oxides are broken up into nitrogen and oxygen gases, which on their own are harmless.
  • Oxidation catalysts: Used to change carbon monoxide into carbon dioxide through an opposite process of adding oxygen. "
1705843080615.png


Maybe you have the reduction type on your car? Or, with respect to some of the complexities @70bigblockdodge pointed out, there was something else going on?

Hopefully all this conversation is helpful to the OP. It certainly seems that catalytic converters need some detailed thought and design to get them to work properly on a car!
 
So I think I have to say I was wrong here. It seems like catalytic converters like heat to operate, so it seems location might matter a lot.


I decided to look it up, since I obviously do not have a good grasp on catalytic converter details. It seems there are two kinds of converters.

Per a UTI article (What Is a Catalytic Converter and What Does It Do? | UTI): "There are two main types of catalysts that might be featured in a car:
  • Reduction catalysts: Help reduce nitrogen oxide pollution by removing oxygen. Nitrogen oxides are broken up into nitrogen and oxygen gases, which on their own are harmless.
  • Oxidation catalysts: Used to change carbon monoxide into carbon dioxide through an opposite process of adding oxygen. "
View attachment 1595716

Maybe you have the reduction type on your car? Or, with respect to some of the complexities @70bigblockdodge pointed out, there was something else going on?

Hopefully all this conversation is helpful to the OP. It certainly seems that catalytic converters need some detailed thought and design to get them to work properly on a car!
I think both types of catalysts are inside the same catalytic converter….pretty sure anyway, not 100%
 
I think both types of catalysts are inside the same catalytic converter….pretty sure anyway, not 100%
Yes, I believe you are correct, for newer catalytic converters. Older ones (maybe pre mid 80s?) didn't do the NOx.
 
But charger smells exactly like my father’s car from childhood, and it kills me in a second. The difference is only cats I assume.
Maybe you had some CO poisoning from back then. I believe it to have long term lasting effects.
 
Yes, I believe you are correct, for newer catalytic converters. Older ones (maybe pre mid 80s?) didn't do the NOx.
I do believe the older ones did not do oxides they used EGR for that. Most new (1996 and newer OBD2 cars) have slowly eliminated the EGR.
From my limited knowledge oxides are created by superheated combustion. Mostly caused by lean mixtures, which is what all modern cars fuel systems strive for, but there is a tipping point, which OBD2 controls do very well for literally hundreds of thousands of miles. I have a 2002 trailblazer that still passes the emissions except for evap system that has nothing to do with performance, just plastic line connectors and rubber grommets that are 20+ years old.
@Cranky your emission problem fixed with lower block temp and air filter/no air filter putting afr into proper parameters for a OBD1 system that has narrower ranges and can't correct for poor tune up, I miss the old system where a set of plugs, air filter and a oil change could get you through emissions.
I think OP problem is carbon monoxide poisoning. Cats would help and I think @PurpleBeeper a cat for a more period car like 75-78 might be right idea.
 
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