Ok, the 87-92 Stangs came with 4 cats...2 on each side. I was wondering if you were to get an aftermarket X or H pipe and only get 1 cat on each side, would it still be able to pass emission testing? I have always wanted to know this.
A Cat Question
- Thread starter 87MustangGT5.0
- Start date
Michael Yount
Mustang Master
It depends on where it's being tested and even who's doing the visual. There are some locations that are looking for a even replacement cats that mimick the factory set up -- that is, if they're looking for 2 cats on each side and they find only one, you've got a problem.
There are other locations that only care that the cats are there and that you pass the sniffer.
Beware - there are different cats for different jobs. If you're replacing 2 cats with one be sure it's a "3-way" cat you're getting - one that's set up to treat HC, CO and NOx. Both of the factory cats are needed to treat all 3 emitants - the first and second cats are different from each other.
There are other locations that only care that the cats are there and that you pass the sniffer.
Beware - there are different cats for different jobs. If you're replacing 2 cats with one be sure it's a "3-way" cat you're getting - one that's set up to treat HC, CO and NOx. Both of the factory cats are needed to treat all 3 emitants - the first and second cats are different from each other.
I have not had a problem here in California. I believe that the rule says that you can only change cats when the car has a certain number of miles, and the cats are diagnosed as broken or inoperable. But I am unaware of any standard for what constitutes a "replacement" cat at that point. I don't know that a muffler shop is bound to install exact replacement convertors, or if any number of aftermarket ones of the same general type will do. The same goes using for 4 versus 2. I have a hard time believing that an authorized shop asked to replace worn out cats would go to the trouble of welding in 4 cats, if they could even do it. I think as long as the smog test guys see an actual cat in the pipe under the car, they proceed with the tailpipe sniff. I have been running a high flow 2.5" cat h-pipe with only 2 cats for 6 or seven years now, which is at least 3 smog test cycles, and have not had a single issue. Plus, I pass with flying colors, so it's difficult to say there is even a meaningful difference. Indeed, my GT40 head/E303 cam/MSD6A/Mac shorty/BBK h-pipe/Flowmaster '90 LX hatchback blows cleaner out the pipes than my identical but completely stock '90 LX convertible, which I attribute at least in part to the fact that the BBK pipe has only 15k miles on it, while the stocker has 135k miles on the original cats. I think you are actually doing the air a favor by upgrading rather than continuing to drive on worn out cats.
Michael Yount
Mustang Master
Good catch Sam - I missed the sig completely - how a car that's originally efi which has been converted to carb is gonna pass the visual let alone the sniffer -- well, I suspect some sort of bribe is the only way to a 'sticker'.
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