I have a 94 f350 7.5L that the previous owner cut out the cat and did a complete 3" single exhaust all the way back on. Truck also has an intact air pump system, including the one that dumps into the exhaust right before the cat (well, where the cat used to be). I want to put a catalytic converter back on, as I know it won't pass a visual emissions inspection and I'm almost certain it won't pass the sniffer emissions test also as it sits. The exhaust stinks.

I searched around and see a lot of different options for aftermarket catalytic converters ranging from "high flow" 49 state legal to OEM replacements, from anywhere around 80 bucks to 300+. What should I be looking for here? Will any "universal fit" 3" inlet/outlet cat work, or do I need something special? Why is there such a range of prices, even in the aftermarket selection (flowmaster, magnaflow, etc)?

In the past, I have heard that the reason for the air pump line that dumps right before the cat on these trucks was due to the "early" or "primitive" style of converter that needed the extra oxygen to burn off particulates. Is that accurate? Is the air injection needed with "modern" replacement or aftermarket cats?

I have a welder and am confident I will have no problem cutting a section of the existing 3" piping out and fitting a new catalytic converter in, I just want to make sure I get the right one for the truck at a reasonable price. Anyone have any input?

 

Just about any 3" cat will do, but they have ratings for cubic inches attached to the specifications of each ...just make sure the one you buy is rated for 460. Stick with a hi flow, they're cheap and don't rob much power.

the air injection can go, the only cat replacements that use the injection are factory direct replacements.

 

Just replaced everything from the front pipe back with Walker OEM style converter , muffler,tailpipes. Had to add length to the cat inlet and cut the length of the outlet to make all of the hangers and air pipe line up,but other than that all worked out great . 93 F-350 7.5

 

Wonder if a 7.3 cat removed to install a full exhaust system would work?

 

Diesel cats generally aren't three way catalysts, as used on gas engines.

 

All aftermarket cats are Hi flow compared to OEM so you don't need to pick on that is specifically rated as such. And you do get what you pay for with these things, it seems that with the cheapest cats the material used to hold the catalyst medium in place inside the can deteriorates and then you get that familiar metal on metal rattling sound after a year or two of use.

 

When I did the exhaust on my 96 460 truck back .......14 years ago I went with a universals 3" stainless cat WITH the air injection tube.

In NJ you were allowed 300 PPM CO2. With the high flow cat it put out 3 PPM.

YES 3.

Exhaust is still on the truck to his day

 

Brad, do you mean CO and not CO2?

I'm not super familiar with emissions testing but I don't understand how a cat is going to remove that much CO2 from exhaust without sequestration. CO yes, oxidize it to CO2. But with CO2 and water already being the primary combustion products..well, it's not adding up. Quick reading looks like CO2 isn't measured/regulated directly.

 

CO2 Carbon Dioxide..
CO is cobalt

 

I'm maybe being picky, but...
Co is cobalt (not involved in fuel combustion), CO is carbon monoxide (product of incomplete combustion, poisonous, regulated, readily oxidized to CO2 in a catalytic converter), CO2 is carbon dioxide (product of complete fuels combustion, non-poisonous, ubiquitous greenhouse gas, currently unregulated, no stable way to further oxidize).

 

CO2 is Carbon Dioxide
CO is Carbon Monoxide.
Co is Cobalt

I think GoingBoarding is correct and that you're mixing up CO2 and CO numbers. 3 PPM CO2 from a running engine is pretty much impossible. The exhaust of most running vehicles is around 15% CO2 - or 150,000 PPM.

 

I wish I still had my print out. I was in utter amazement. 3 PPM CO2

 

Your catalytic converter oxidizes carbon monoxide (CO), turning it into carbon dioxide (CO2), actually increasing the carbon dioxide (CO2) output of your engine.

 

It was a typo on the printout then. The chemistry doesn't work that way. That is a good catalyst though.

 

Emissions tests typically measure carbon monoxide (CO), unburned hydrocarbons (HC) and oxides of nitrogen (NOx).

CO and HC are the result of incomplete combustion. Catalytic converters finish what the engine was trying to do, oxidize (another word for "burn" in this case) those to form carbon dioxide (CO2) and water (H2O). So with a perfect burn (in the engine, cat or both combined) there would be no CO or HC.


NOx is from too hot of a burn. It's also a pollutant. I'm not sure what a cat does with it.