Currently I have the dual cat system on my 1991 z28 and would like to use the MAC headers that I purchased (before I got the car). The headers I bought have all of the air connections but are for a single 3" cat. I am just wondering if this would be emissions legal since both systems were offered in 1991.

 

I cant see that being a problem. As long as you still have A cat in there. Id be surprised if most people even noticed that you only have 1 cat in place of the 2.

 

From what I understand it can be illegal, depending on how strict your emmissions stations are. Now I don't know for a fact but I have heard that if your car has dual cats and you go in with only 1 there, they will fail you. The rumor is that the emmisions stations have a list of how many your car is supposed to have. How true this is I'm not sure. Your best bet would be to find someone locally that has done the swap and made it through. You could also talk with an exhaust shop, they may know. As a last effort, you could call the emissions station and find out for sure. Make up some story like you bought the car and it has no exhaust and your are going to put one on it, what do you need to be able to pass an emmisions test/inspection. Make up something, that way they don't give you a hard time.

Hope that helps.

 

You could always move somewhere where it doesn't matter

 

If that model car came with either dual or single cats, you can run either, and nobody will make any stink. If you have a 350 and they only came with dual cats, if the guy asks, tell him it is now a 305. The emissions regs are the same for both engines. The smog guys are more looking to make sure there IS a cat.

Troy
So Cal

 

The important thing is to have the working Cat and pass the emmission standards. The people working at these test sites are not engineer types and do what they are told if that. So don't worry about it. All they do is run the Vin number to verify that it is the correct car and you know what the Vin tells you. Almost nothing.

 

3" single cat wasn't available in '91.

The chances of the inspector noticing or caring is next to nil.

California might be a different matter, but even then it would almost have to be an inspektor that was out to get you before he saw the converter.

 

Another option would be to chop off the "Y" of the Mac y-pipe and run individual pipes to the cats.

 

I think I am going to go with the single 3" cat, use my mac headers, and get a random tech stainless steel catback. I bought the car from 86fyrbrd and he dynoed it and got 232hp and 317 lb/ft of torque at the rear wheels. When I went to get it inspected the other day I noticed that the y-pipe and exhaust was all crush bent pipe (it has edelbrock TES headers). I was wondering what you guys think I might pic up at the rear wheels going with the exhaust I mentioned.

 

TES should have come with mandrel bent down-pipes to the cats.

If it has TES headers with dual cats now, going to the Mac with single cat isn't going to make much difference. Even if the current pipes aren't mandrel bent and the Mac are. The cat-back may be an improvement, depending upon how "bad" your current system is.