Interesting exhaust discovery...(cat related) - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

DarkneSS · 11-07-2011, 12:01 PM

I had new DMH cutouts welded in on friday morning. Ill be posting pics soon. GREAT quality electric cut out they dont leak whatsoever.

I had the muffler shop cut off the smaller of the two cats on each side and had them place the dump pipes directly behind the bigger cats. Ill post images and video soon Im just a bit busy.

Whats interesting however is that ive driven about 300 miles since then, about 100 of those miles with the exhaust open the entire time and I HAVE NOT thrown an engine code!

Im going to put more miles on of course but honestly if it was going to throw a code it would have happened by now. Who knows though it may still pop up.

So essentially it seems we all can safely remove the last two cats on each exhaust pipe without throwing any codes.

The performance increase is probably something like 1-2 whp but its still a gain. No way to back up that claim but any engine will always make more power with less cats.

So again not much of an increase in performance if any at all but it seems you can remove these cats.

The usefulness of this is if you're like me and dont want to throw any codes and run cut outs. Removing the last two cats gives you room to weld the dump pipes in safely.

Ill edit later with photos and video.

TJ91 · 11-07-2011, 12:12 PM

that is definitly an interesting find. Keep us posted !

bmorecam · 11-07-2011, 12:32 PM

Sometimes it will take 1000 miles and sometimes 2, but when you remove the 2 rear cats you better believe you will get the cat efficiency CEL. The only way to get by this is via tuning.

KMPrenger · 11-07-2011, 12:38 PM

I have to agree with bmorecam...I believe eventually you are going to see the CEL....but hopefully yours will be an exception and not throw a code!

MichaelH · 11-07-2011, 12:50 PM

bmore is right it took about 200 miles for my lt headers to finally throw a code on my car

scrming · 11-07-2011, 01:24 PM

There should NOT be a CEL when you remove the rear cat because it is AFTER the final O2 sensor:

The reason you get a CEL with headers is because you are changing stuff IN FRONT of the O2 sensors, especially the final O2 sensors...

The reason you get CEL with the JBA's is because the stacker flange, that apparently leaks is BETWEEN the front O2 sensor and the rear O2 sensor:

You can see the front O2 sensor here:

The rear O2 sensor is AFTER the flange... the flange can leak and can trigger the CEL...

rtcat600man · 11-07-2011, 01:36 PM

Quote:

Originally Posted by scrming

There should NOT be a CEL when you remove the rear cat because it is AFTER the final O2 sensor:

The reason you get a CEL with headers is because you are changing stuff IN FRONT of the O2 sensors, especially the final O2 sensors...

The reason you get CEL with the JBA's is because the stacker flange, that apparently leaks is BETWEEN the front O2 sensor and the rear O2 sensor:

You can see the front O2 sensor here:

The rear O2 sensor is AFTER the flange... the flange can leak and can trigger the CEL...

Now that makes sense to me. Thanks

KMPrenger · 11-07-2011, 02:15 PM

ahhh...I forgot the rear 02 sensor was in front of the rear cat....woops!

Now I change my answer! lol

gotexas25 · 11-07-2011, 02:23 PM

what would this do for sound? more rasp, a little louder? I'm all about getting that extra 1 or 2 hp

TJ91 · 11-07-2011, 03:10 PM

Quote:

Originally Posted by KMPrenger

ahhh...I forgot the rear 02 sensor was in front of the rear cat....woops!

Now I change my answer! lol

LOL

rtcat600man · 11-07-2011, 08:51 PM

Quote:

Originally Posted by gotexas25

what would this do for sound? more rasp, a little louder? I'm all about getting that extra 1 or 2 hp

I will let you know next April. I will have my OBX headers installed by then.

OOLIE · 11-07-2011, 09:26 PM

The extra flow could lend to more rasp. OBX is no cats so it would be even more possibly. Depends on the exhaust you have as to how bad it might be, but there is always the res x pipe to help.

I think stock manifolds and one less cat probably is not a big flow issue as far as rasp. That is just a hunch

tmac1granger33 · 11-07-2011, 10:22 PM

how much did you spend on the DMH cutouts?

bmorecam · 11-07-2011, 10:41 PM

Quote:

Originally Posted by scrming

There should NOT be a CEL when you remove the rear cat because it is AFTER the final O2 sensor:

The reason you get a CEL with headers is because you are changing stuff IN FRONT of the O2 sensors, especially the final O2 sensors...

The reason you get CEL with the JBA's is because the stacker flange, that apparently leaks is BETWEEN the front O2 sensor and the rear O2 sensor:

You can see the front O2 sensor here:

The rear O2 sensor is AFTER the flange... the flange can leak and can trigger the CEL...

I guess that's why you can still drive the "TAXI" truck and still be scrming round here

I have to admit, you are always 99% correct

11-07-2011, 12:01 PM	#1
DarkneSS Account Suspended Drives: 2010 Camaro 2SS/RS 6MT Join Date: Apr 2010 Location: Westchester, New York Posts: 3,715	Interesting exhaust discovery...(cat related) I had new DMH cutouts welded in on friday morning. Ill be posting pics soon. GREAT quality electric cut out they dont leak whatsoever. I had the muffler shop cut off the smaller of the two cats on each side and had them place the dump pipes directly behind the bigger cats. Ill post images and video soon Im just a bit busy. Whats interesting however is that ive driven about 300 miles since then, about 100 of those miles with the exhaust open the entire time and I HAVE NOT thrown an engine code! Im going to put more miles on of course but honestly if it was going to throw a code it would have happened by now. Who knows though it may still pop up. So essentially it seems we all can safely remove the last two cats on each exhaust pipe without throwing any codes. The performance increase is probably something like 1-2 whp but its still a gain. No way to back up that claim but any engine will always make more power with less cats. So again not much of an increase in performance if any at all but it seems you can remove these cats. The usefulness of this is if you're like me and dont want to throw any codes and run cut outs. Removing the last two cats gives you room to weld the dump pipes in safely. Ill edit later with photos and video.

11-07-2011, 12:12 PM	#2
TJ91 :chevy: Drives: 2LT/RS Join Date: Jun 2008 Location: Toronto Posts: 13,033	that is definitly an interesting find. Keep us posted ! __________________ CAMARO Consult your doctor before taking Camaro Side effects include Sudden increase in Heart Rate, Insomnia and occasional hallucinations If you experience Permagrin exceeding 4 hours after taking Camaro, seek immediate Camaro5 Help CAMARO Bringing excitment back into the Garage

11-07-2011, 12:38 PM	#4
KMPrenger Drives: 16 Camaro SS, 15 Colorado Join Date: May 2009 Location: Jefferson City, Missouri Posts: 13,943	I have to agree with bmorecam...I believe eventually you are going to see the CEL....but hopefully yours will be an exception and not throw a code! __________________ 2016 Camaro 1SS - 8-speed - NPP - Black bowties 2010 Camaro 1LT V6 (Sold. I will miss her!)

11-07-2011, 12:50 PM	#5
MichaelH SOCAL HT5 Drives: 2013 BRM ZL1 M6 Join Date: Apr 2010 Location: NE Ohio Posts: 1,495 View My Garage	bmore is right it took about 200 miles for my lt headers to finally throw a code on my car __________________ 2013 ZL1 M6 - Mods-in the works Old vehicles 2010 CGM Camaro (sold) Other Vehicles: 2008 Kawasaki ZX6R-115 RWHP in mid summer 2006 Chevy Trailblazer SS- For Sale; Lots of extras

11-07-2011, 01:24 PM	#6
scrming Red Brick of Vengeance! Drives: 12 Second Brick Join Date: Jun 2009 Location: at my pulpit Posts: 7,745	There should NOT be a CEL when you remove the rear cat because it is AFTER the final O2 sensor: The reason you get a CEL with headers is because you are changing stuff IN FRONT of the O2 sensors, especially the final O2 sensors... The reason you get CEL with the JBA's is because the stacker flange, that apparently leaks is BETWEEN the front O2 sensor and the rear O2 sensor: You can see the front O2 sensor here: The rear O2 sensor is AFTER the flange... the flange can leak and can trigger the CEL... __________________ 2011 Ford Flex EcoBoost Limited - 12.727 @ 109.790 MPH

11-07-2011, 12:32 PM	#3
bmorecam Account Suspended Drives: jealous vendors mad!! HAHA!! Join Date: Jan 2011 Location: CYBERGMONSTER@GMAIL.COM Posts: 3,658 View My Garage	Sometimes it will take 1000 miles and sometimes 2, but when you remove the 2 rear cats you better believe you will get the cat efficiency CEL. The only way to get by this is via tuning.

11-07-2011, 02:15 PM	#8
KMPrenger Drives: 16 Camaro SS, 15 Colorado Join Date: May 2009 Location: Jefferson City, Missouri Posts: 13,943	ahhh...I forgot the rear 02 sensor was in front of the rear cat....woops! Now I change my answer! lol __________________ 2016 Camaro 1SS - 8-speed - NPP - Black bowties 2010 Camaro 1LT V6 (Sold. I will miss her!)

11-07-2011, 02:23 PM	#9
gotexas25 Camaroholic Drives: 2010 2LT RS Join Date: May 2010 Location: Houston Posts: 130	what would this do for sound? more rasp, a little louder? I'm all about getting that extra 1 or 2 hp

11-07-2011, 09:26 PM	#12
OOLIE Drives: 2011 LS Join Date: Oct 2010 Location: FL Posts: 1,643	The extra flow could lend to more rasp. OBX is no cats so it would be even more possibly. Depends on the exhaust you have as to how bad it might be, but there is always the res x pipe to help. I think stock manifolds and one less cat probably is not a big flow issue as far as rasp. That is just a hunch __________________

11-07-2011, 10:22 PM	#13
tmac1granger33 NM HT5 Drives: COTW 3/5/12 Join Date: Jul 2009 Location: los lunas, New Mexico Posts: 1,986 View My Garage	how much did you spend on the DMH cutouts?

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