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post #1 of 14 (permalink) Old 07-18-2016, 06:07 PM Thread Starter
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Two cats better than one?

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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post #2 of 14 (permalink) Old 07-18-2016, 06:12 PM
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You can't have 2 cats, it would screw up the HOČs. He doesn't know what he's talking about. You should have an exhaust Manifold with a pre cat HOČ then a flex pipe, the the cat, then the downstream HOČ 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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post #3 of 14 (permalink) Old 07-18-2016, 06:16 PM Thread Starter
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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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post #4 of 14 (permalink) Old 07-18-2016, 07:50 PM
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Could be he monkeyed something together.

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post #5 of 14 (permalink) Old 07-18-2016, 08:05 PM
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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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post #6 of 14 (permalink) Old 07-18-2016, 08:26 PM Thread Starter
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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?

Last edited by ChaseChevy; 07-18-2016 at 08:34 PM. Reason: Post was interrupted
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post #7 of 14 (permalink) Old 07-18-2016, 09:33 PM
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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.

1986 Chevrolet Camaro IROC-Z - Wrecked/Sold
1998 Chevrolet Cavalier - Wrecked/Donated
2007 Chevrolet Cobalt LT - M62 Supercharger, Ported Throttle Body, 42 lb/hr Injectors, Intense 2.9" Pulley, Cobra Heat Exchanger, SS/TC Exhaust, TTR Engine and Trans Mounts, Trifecta Tune, ZZP Header and Downpipe, '08+ FE5 Struts/Shocks, SSC Springs, FE5 Control Arms, SS/SC Front Swaybar, Powell Hardcore Rear Swaybar, 18" MSR 045s, Dunlop ZIIs, Nightshaded Tails/Side Markers, Shorty Antenna, Black Bowties, Black Grilles, Black Headlights, Dual JL 12" w1v2 Subs, A/D/S Front/Rear Speakers, Pioneer 7" Touchscreen, G85 Recaros, Leather Rear Seats, 160 MPH Cluster.
2014 Chevrolet Cruze Diesel - 17" MSR 013s, Black Bowties, Black Tails, UR Rear Lower Bar
1981 Chevrolet Camaro Z28 - JVC Ribbon Tweeters, SEAS Mids, Pyle Woofers, Kenwood Tape Deck, Zapco Amp/Equilizer, Ceramic-Coated Longtubes, 2.5" Pypes Stainless Exhaust, Bilstein B6 Shocks, GW U/L Control Arms, Hotchkis Springs Sway Bars, DD HDX Cluster
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post #8 of 14 (permalink) Old 07-19-2016, 08:40 AM Thread Starter
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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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post #9 of 14 (permalink) Old 07-19-2016, 09:15 AM
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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.

1986 Chevrolet Camaro IROC-Z - Wrecked/Sold
1998 Chevrolet Cavalier - Wrecked/Donated
2007 Chevrolet Cobalt LT - M62 Supercharger, Ported Throttle Body, 42 lb/hr Injectors, Intense 2.9" Pulley, Cobra Heat Exchanger, SS/TC Exhaust, TTR Engine and Trans Mounts, Trifecta Tune, ZZP Header and Downpipe, '08+ FE5 Struts/Shocks, SSC Springs, FE5 Control Arms, SS/SC Front Swaybar, Powell Hardcore Rear Swaybar, 18" MSR 045s, Dunlop ZIIs, Nightshaded Tails/Side Markers, Shorty Antenna, Black Bowties, Black Grilles, Black Headlights, Dual JL 12" w1v2 Subs, A/D/S Front/Rear Speakers, Pioneer 7" Touchscreen, G85 Recaros, Leather Rear Seats, 160 MPH Cluster.
2014 Chevrolet Cruze Diesel - 17" MSR 013s, Black Bowties, Black Tails, UR Rear Lower Bar
1981 Chevrolet Camaro Z28 - JVC Ribbon Tweeters, SEAS Mids, Pyle Woofers, Kenwood Tape Deck, Zapco Amp/Equilizer, Ceramic-Coated Longtubes, 2.5" Pypes Stainless Exhaust, Bilstein B6 Shocks, GW U/L Control Arms, Hotchkis Springs Sway Bars, DD HDX Cluster
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post #10 of 14 (permalink) Old 07-19-2016, 09:36 AM
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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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