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Discussion Starter #1
Hey folks, I just got all new exhaust today. New MagnaFlow cat, 2.25 pipes and 14 inch offset MagnaFlow muffler with a real sweet 3 inch chrome tip...
The muffler guy, Steve, said there was two cats up under there along with a resonator. I had never slid up under it to see what it looked like so can't say I saw those cats... So why would there had been two of them? Anywho it sounds damn good and performance wise it's improved nicely..
 

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You can't have 2 cats, it would screw up the HO²s. He doesn't know what he's talking about. You should have an exhaust Manifold with a pre cat HO² then a flex pipe, the the cat, then the downstream HO² then a length of pipe, then a resonator, then an other length of pipe, then the muffler and finally the tail pipe.
 

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Thats what I thought. Is it possible some greeny that had the car before me thought an extra one after the downstream sensor would be a good idea.
 

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Could be he monkeyed something together.
 

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Some 2.2L downpipes came with two cats from the factory. The LNF has two as well.

 

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Discussion Starter #6 (Edited)
Imagine that
Why would they put two on there? And I assume, judging from that pic, that there wasn't another sensor in there totaling 3 sensors?
 

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My guess is it is in a location with stricter emissions standards or something - or it may have been an early design that was superseded by the single cat. Mine only had one.

No extra sensor, correct.

---------- Post added at 11:33 PM ---------- Previous post was at 11:29 PM ----------

Some real quick sleuthing on the "other" site, and it looks like cars with SAI (secondary air injection) have the two cats on the downpipe.

It would seem they are not a three way cat - the two have the separate functions you usually find in a single three way cat.
 

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My Cobalt doesn't have SAI. I also read what I think you read on the "other" site and someone said their buddy's car didn't have SAI but appeared to have two cats.
I think they were putting these on cars to get rid of them maybe? It's no big deal it's just got me curious is all.
One thing I do know is getting rid of mine, putting on MagnaFlow and bigger pipes worked out real nice. It's not all mandrel bent stainless steel but better nonetheless.
 

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It's possible once they phased out SAI that they had leftover stock so they used it up. Very common in the auto industry.
 

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My 2010 LT had 2 cats on the downpipe. Dunno why they did it for Oklahoma, since I don't think our emissions standards are particularly high.
 

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Is your car a manual or auto?
 

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Mine has 2 cats and its an 08 and manual.

---------- Post added at 11:58 AM ---------- Previous post was at 11:58 AM ----------

And where i am they dont bother with any emission testing
 

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I believe the second canister is called a flame suppressor or arrestor, they got rid of it later when they realized the resonator was doing the same thing pretty much and by shutting down the fuel before locking the torque converter during engine braking.
 
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