best universal Catalytic converter

[BrianAbington]

wow, its been close to a year since I've been on here.

Life has been crazy...long story really short...My wife still has the kia spectra, I now have a 94 F-150 5.8L 4x4.

I have a set of ceramic coated aftermarket headers, and will be doing a full exhaust. I need a new cat though.

Since we will be moving to washington state, I need to pass emissions testing.

I am leaning towards ceramic core material...however I'm open to metalic cores I just need some input.

Who makes the best 3" input high flow cat, one that will flow well, yet will do a great job cleaning the exhaust but not need to be replaced after a fewmonths because of a design flaw?

[AeroModder]

Higher flow=less filtering, unless it's some kind of revolutionary material. Most high flow cats are illegal for use in California because they don't filter as well, but I'm not sure about Nebraska's laws. Your best bet for clean air is a stock replacement.

[PaleMelanesian]

Motor Trend or Hot Rod or some other magazine tested a Camaro, and it actually ran better dyno numbers WITH the stock cat in place, compared to open pipes or a high-flow cat.

[comptiger5000]

Aeromodder - In theory, a high flow can filter just as well. However, it has to be bigger to accomplish this. The more area it has exposed, the better it will filter, and given enough passages for exhaust to pass through (large enough size), it can be effective and flow well.

[Piwoslaw]

Originally Posted by comptiger5000

Aeromodder - In theory, a high flow can filter just as well. However, it has to be bigger to accomplish this. The more area it has exposed, the better it will filter, and given enough passages for exhaust to pass through (large enough size), it can be effective and flow well.

A catalytic converter doesn't just filter in the normal sense, as a fuel or oil filter does, it uses platinum as a catalyst (hence the name) to convert poisonous exhaust into slightly less poisonous gasses.
But the more area that is exposed, the less that area warms up (spreading the same thermal energy over a larger surface). A cat works only when heated above a certain temperture, that's why cold starts are so bad on emissions. If you are drag racing your car all the time, then the exhaust gasses will be hotter and can warm the larger area, but a hypermiler's exhaust tends to be slightly cooler than normal (since he is using less fuel to do the same job, thus wasting less energy as heat in the tailpipe).
So, the larger the internal area of the new cat, the smaller that chances that it will do its job, especially if you hypermile.

[roflwaffle]

Offhand I'm guessing the effectiveness of the cat if it's a bit larger depends on whether or not the vehicle in question has a post cat sensor to monitor operation and the appropriate code to run richer and light off the cat faster if it detects excessive HC emissions at whatever time during warmup.

[BrianAbington]

I honestly think that in nebraska you would have to roll your car on its roof and an officer would have to casualy notice you had no cats for anybody to say anything about it.

only inspection we have here is they make sure the vin on the car is the same as the one on the title and thats only if you bought the vehicle out of state.

The stock cat on this truck has a tapered entrance that narrows down to like 2".

My headers have 3" collectors and I want to make it as free flowing as possible. I know about the surface area issue I was just wanting to know if there has been a test on whos cat was cleanest.

[comptiger5000]

Pinoslaw - Good point. I hadn't though about the low exhaust temp due to hypermiling. However, for those with larger engines, it might still be viable.

For example, on my Jeep, if I start it on a cold morning, in the time it takes for me to get out of it and walk to the back end immediately after startup, it's already steaming notably out the exhaust. While driving, it steams all the condensation out of the exhaust within 2 miles or so.

[Piwoslaw]

Originally Posted by roflwaffle

Offhand I'm guessing the effectiveness of the cat if it's a bit larger depends on whether or not the vehicle in question has a post cat sensor to monitor operation and the appropriate code to run richer and light off the cat faster if it detects excessive HC emissions at whatever time during warmup.

Ah, didn't think about that. If this is the case, then the richer burn will keep the catalyst within operating parameters, but at the expense of greater fuel consuption, which what using a larger cat was supposed to reduce in the first place. I'm willing to bet that in this case stock is the best way to go, unless you're ready to do some difficult and expensive A-B-A-B testing (which we would love to see the results of).

[bgd73]

Originally Posted by PaleMelanesian

Motor Trend or Hot Rod or some other magazine tested a Camaro, and it actually ran better dyno numbers WITH the stock cat in place, compared to open pipes or a high-flow cat.

if homogeny is designed around the cat it will be like that. I found pre-mid 90s could be a nasty cat and aftermarket is welcome on alot of american.

the 1994 is right in the middle someplace...hard telling what it needs.buy a magnaflow, common name. bigger headers is gonna slam oem, not good, and its coated to be hotter down the line. high flow welcome is my guess..not cheating emissions, the change would be to get it correct. I also found stepping up igntion fire is a must do if you open the engine exhaust side...that is also another reason to get the higher flow cat, they go together.

make big noise..you aint got a big engine yet.
I would hope this is beyond an old school day dream to just make big noises.It needs other things to get it right.