dual cats?

[98sierra71z]

i have a 98 sierra z71 with a 5.7 liter and i noticed that there are two cats instead of one.. is this stock or did the previous owner have dual exhaust on it? i am also thinking about putting duals on it and im wondering if it will work with these two cats and make the air flow better?

 

 

thanks,

Brian

[sleepur606]

Before you do anything, look at both cats to see if there are signs of welding on the exhaust pipe. Most of the factory exhaust is real neat, any aftermarket work is at least a little sloppy and there's more spatter from the MIG welding.

But are you sure it's two cats and not just a resonator? I know on my truck it looks like there's an extra set, two big coffee can types, between the real cats and the muffler. Anyway, putting two cats on a car is pretty much a joke in the auto industry, if you have to double cat it, something else is wrong.

One easy way to check it, as the 98 truck should be OBDII...check for oxygen sensors. There should be one between the exhaust manifold and the cat and one either in the middle of the cat or just after. If the "second cat" you're talking about is after both cats it's most likely a resonator.

For clarification, I'm not a tech...I'm a 20 year old taking automotive classes while trying to get transfer credits at a local JC, so take everything with a little grain of salt.

[hercman]

98 C1500s have dual cats.

[srlbotanical]

98 C1500s have dual cats.

 

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Exactly, The OBS 5.7 had duel cats that feed into a single big muffler which then dumps into one tail pipe.

 

Supper easy to convert to a true duel system. You can buy a cat-back exhaust set up from one of the big manufacturers, but its a lot cheaper to buy your mufflers of choice (flowmaster in my case) cut off the stock system just before big stock muffler and have a good local shop bend out the pipes for you.

 

Steve