Catalytic converts with sniper EFI? Due to health related problems

[DodgeBall]

Modern cats will make a huge difference. I know someone who took cats off of a stock modern V8 and the car stinks like a 60s car. As stated by others, mount them as close to the manifold as possible. Use the newest cats you can find (or quality aftermarket replacements for a new car such as a V8 Challenger or Mustang GT). I know your engine is big, but a cat that is a little on the small side is probably better because it will heat up quicker and stay hotter (yes it might cost a little horsepower up top). Don't get high flow. Get cats designed for a car that only had two cats from the factory...you don't want two from a car that was designed with four, because they may do different things. Make sure your fueling is dialled in because a rich mixture can wreck your new cats. Just in case that happens, I'd suggest clamping them in place rather than welding them...use some high temp sealant to seal them up. Good luck!

 

[GiantRobo]

I wanted to put cats on my 68 Charger, but my father in law (who tunes EFI systems professionally) said I couldn't do that. The base sniper unit only has one oxygen sensor. You need a system with upstream and downstream sensors to make the cats work.

In addition to what everyone said, there could be a lot going on here. Some people are just more sensitive to smells. There's times people complain about a smell and I say "what smell?!?"

Classic cars are just poorly sealed against gasses, no matter what, compared to modern cars. I used to get car sick as a kid in the 70s, just from gas fumes coming into the car from the carb.

Dumb question: is it a non-AC car? Make sure your fresh air vents are closing fully and sealing completely. They could be letting gas into the car.

Also, how sealed is your exhaust? Headers? Exhaust manifolds? A potential source of leaks. There's gaskets made of graphite that seal really well to the block. If running headers do the same for the collector gaskets. Then have the rest of the system _welded_, not clamped.

Are your exhaust tips tucked under the bumper, or sticking out? Another potential source to let gas in.

If the trunk isn't sealed, could be another problem. You're going to check the lid seal, but you could add a plastic barrier or tape to the trunk panel behind the back seat, just in case.

 

[Don Frelier]

I wanted to put cats on my 68 Charger, but my father in law (who tunes EFI systems professionally) said I couldn't do that. The base sniper unit only has one oxygen sensor. You need a system with upstream and downstream sensors to make the cats work.

In addition to what everyone said, there could be a lot going on here. Some people are just more sensitive to smells. There's times people complain about a smell and I say "what smell?!?"

Classic cars are just poorly sealed against gasses, no matter what, compared to modern cars. I used to get car sick as a kid in the 70s, just from gas fumes coming into the car from the carb.

Dumb question: is it a non-AC car? Make sure your fresh air vents are closing fully and sealing completely. They could be letting gas into the car.

Also, how sealed is your exhaust? Headers? Exhaust manifolds? A potential source of leaks. There's gaskets made of graphite that seal really well to the block. If running headers do the same for the collector gaskets. Then have the rest of the system _welded_, not clamped.

Are your exhaust tips tucked under the bumper, or sticking out? Another potential source to let gas in.

If the trunk isn't sealed, could be another problem. You're going to check the lid seal, but you could add a plastic barrier or tape to the trunk panel behind the back seat, just in case.

An O2 sensor doesn't make the Catalytic converter work it just measures the result.
Way back when they first started to put them in cars they had a carburetor and no sensors at all (and no computer controlled engine control).
The only reason they have 2 on cars today is to adjust and determine performance and efficiency.
Mainly to detect if the converter is functioning properly.
You could certainly put a converter on but just put it downstream of the O2 sensor.

 

[GiantRobo]

An O2 sensor doesn't make the Catalytic converter work it just measures the result.
Way back when they first started to put them in cars they had a carburetor and no sensors at all (and no computer controlled engine control).
The only reason they have 2 on cars today is to adjust and determine performance and efficiency.
Mainly to detect if the converter is functioning properly.
You could certainly put a converter on but just put it downstream of the O2 sensor.

Maybe I misunderstood him then. He was pretty certain my first gen Sniper wouldn't handle a cat well, because it didn't have that second sensor. Could be he was thinking of it from an efficiency perspective. Honestly he was info dumping on me pretty hard as he was going through the fuel maps, etc. while he tuned it.

Regardless, another thing mouserider could try is getting a tune for the EFI. That will help make sure the system's running at peak, assuring best a/f ratio, reducing emissions, etc. Holley provides a very generic map out of the box which doesn't really factor in all combinations. Yes, it "learns", but within a range.

When we tuned my stroker it was very over rich at low rpms and more lean than it should be at higher. This after the car had been 'self-tune' driven thousands of miles by two previous owners. Tweaking the tune fixed all that and picked up idle vacuum to boot (still not enough for good PB, but better...)

 

[Davison]

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.

You should give Flowmaster a call. I looked at their website. They have plenty of catalysts available; prices are just above $100 to a bit over $200. Some are on sale now. A few detailed descriptions say they are for 1966 and later vehicles. Anyway, they seem to have a demand for catalysts on pre-catalyst cars, so they probably can answer your installation questions. Good luck and let us know if you do it.