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Old 04-15-2013, 05:33 AM   #1
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Cat delete & O2 sensors?

So besides a UD pulley, I am getting lots of peer pressure to do the cat delete as well. Gosh, this site takes me back sometimes! (Just do it, you'll like it....)

So....

1) is it legal to remove the cats?

2) if I tie-wrap the O2 sensor under the car, why does the false ambient air reading not cause the car to throw CEL codes? Why does the straight air not cause the car to mix or run different?

I just need all the facts before heading down yet ANOTHER fork on Boxster Road....

Thanks, Tim
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Old 04-15-2013, 05:38 AM   #2
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Tie wrap will not work with your MY DME. You will need a row flash to properly eliminate the secondary O2. Running without cats is definitely not legal. Running with a single cat, configured differently than stock is a grey area that will depend on your state's laws...
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Old 04-15-2013, 05:45 AM   #3
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your secondary cats are not monitored. they are after your 02 sensors . you will not have any CEL .
Quote:
Originally Posted by Timco View Post
So besides a UD pulley, I am getting lots of peer pressure to do the cat delete as well. Gosh, this site takes me back sometimes! (Just do it, you'll like it....)

So....

1) is it legal to remove the cats?

2) if I tie-wrap the O2 sensor under the car, why does the false ambient air reading not cause the car to throw CEL codes? Why does the straight air not cause the car to mix or run different?

I just need all the facts before heading down yet ANOTHER fork on Boxster Road....

Thanks, Tim
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Old 04-15-2013, 07:22 AM   #4
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You can replace them with high flow cats. , though this is a more expensive option. Why would you feel pressured to do this? If you don't care about the few H.P. it MAY gain (especially without a "reflash"), just drive it as is and enjoy.
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Old 04-15-2013, 07:57 AM   #5
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You can replace them with high flow cats. , though this is a more expensive option. Why would you feel pressured to do this? If you don't care about the few H.P. it MAY gain (especially without a "reflash"), just drive it as is and enjoy.
Oh, I kid. Every time I think heck, it's a Porsche, its fast enough, I see the same mods listed in sig lines. Then it turns out to be a quick, affordable mod that gives better sound, power, and access so it gets added to the short list. I'm not a track guy, but many of these simple upgrades like the pulley and these pipes are almost no-brainers.
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Old 04-15-2013, 10:46 AM   #6
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i would suggest a highflow cat over a delete, only because there's a enough broke honda kids running around catless, making all the noise in the world and going nowhere fast.
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Old 04-15-2013, 01:03 PM   #7
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Quote:
Originally Posted by Timco View Post
So besides a UD pulley, I am getting lots of peer pressure to do the cat delete as well. Gosh, this site takes me back sometimes! (Just do it, you'll like it....)

So....

1) is it legal to remove the cats?

2) if I tie-wrap the O2 sensor under the car, why does the false ambient air reading not cause the car to throw CEL codes? Why does the straight air not cause the car to mix or run different?

I just need all the facts before heading down yet ANOTHER fork on Boxster Road....

Thanks, Tim

The secondary cats are extraneous ! They can be deleted and bypassed without any concerns for CEL's or OBDII compliance. Get rid of them - and shed the equivalent of a couple of boat anchors !
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Old 04-15-2013, 04:49 PM   #8
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I do not think they quite get it Johnny D

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The secondary cats are extraneous ! They can be deleted and bypassed without any concerns for CEL's or OBDII compliance. Get rid of them - and shed the equivalent of a couple of boat anchors !
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Old 04-15-2013, 06:20 PM   #9
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I assumed when you said cat delete and O2 sensors you were talking about headers. Secondary cats are breeze to remove with no CEL side effects. Don't expect much in the way of performance gains if that's all you do. If anything it's good for weight loss and perhaps improved throttle response...
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Old 04-15-2013, 08:00 PM   #10
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I do not think they quite get it Johnny D
Oh, I do now, and really appreciate having things like this clarified.

Do I search for "secondary cat delete pipes" and is there a recommended brand name?

Thanks.
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Old 04-16-2013, 04:28 AM   #11
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Dump the secondary cats, they are worthless! Nothing is monitored on them (except in the older versions of the Box - you know who you are). The exhaust is stifled at that point too. So not only are you dumping weight, getting a much nicer exhaust note (barely noticeable but there), you are also doing it for virtually no cost! What's not to like? But...no pressure! Top Speed Pro1 makes good cat bypass pipes. If you sell the secondaries on fleabay you can recover most all the cost (about $150).

From what I have observed you may want to consider replacing the Thermostat with a low temp version PRIOR to installing an UD Pulley. Simply put, the devices on your system are running slower b/c of the UD Pulley. I noticed a SLIGHT INCREASE in engine temps as a result. It wasn't much of an increase...but it was not that hot yesterday and I was not running the A/C. With the addition of a low temp thermostat you can be sure your temps will not exceed specs IMHO. But don't let me pressure into that upgrade either.

When you are talking getting rid of the PRIMARY CATS and Headers...that is whole nother kettle of fish! (mine's running great BTW) ...no back pressure!
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Old 04-16-2013, 05:07 AM   #12
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Originally Posted by Timco View Post
Oh, I do now, and really appreciate having things like this clarified.

Do I search for "secondary cat delete pipes" and is there a recommended brand name?

Thanks.
There's a member/vendor on the forum named Che who sometimes has them available. Otherwise, the only reliable source to purchase them from is FabSpeed.
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Old 04-16-2013, 05:38 AM   #13
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Quote:
Originally Posted by Homeboy981 View Post
Dump the secondary cats, they are worthless! Nothing is monitored on them (except in the older versions of the Box - you know who you are). The exhaust is stifled at that point too. So not only are you dumping weight, getting a much nicer exhaust note (barely noticeable but there), you are also doing it for virtually no cost! What's not to like? But...no pressure! Top Speed Pro1 makes good cat bypass pipes. If you sell the secondaries on fleabay you can recover most all the cost (about $150).

From what I have observed you may want to consider replacing the Thermostat with a low temp version PRIOR to installing an UD Pulley. Simply put, the devices on your system are running slower b/c of the UD Pulley. I noticed a SLIGHT INCREASE in engine temps as a result. It wasn't much of an increase...but it was not that hot yesterday and I was not running the A/C. With the addition of a low temp thermostat you can be sure your temps will not exceed specs IMHO. But don't let me pressure into that upgrade either.

When you are talking getting rid of the PRIMARY CATS and Headers...that is whole nother kettle of fish! (mine's running great BTW) ...no back pressure!
No pressure, but "everybody's doing it"...lol.....

I really enjoy these simple doable upgrades so pulley, stat, and pipes it is!

Thanks.
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Old 04-17-2013, 05:32 AM   #14
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As a newbie, the 2ndary cats were the easiest way for me to become familiar with my car, and not screw it up. Since then, I have done many upgrades. This mod is still one of the easiest with the highest probability of success.

BTW, if you have rusted bolts, soak 'em in PB Blaster and let em sit for a while. Also helps to "warm it up" first and let it cool down to work on it.
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Old 01-15-2014, 12:10 AM   #15
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Hello guys,
a quick one,
I own a 986S MY03 European, yesterday I've put straight pipes and car throw CEL, even with secondry O2 sensors connected (hanging around).
Did I miss any step?
Thanks,
Ser
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Old 01-15-2014, 07:05 AM   #16
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Originally Posted by notech View Post
Hello guys,
a quick one,
I own a 986S MY03 European, yesterday I've put straight pipes and car throw CEL, even with secondry O2 sensors connected (hanging around).
Did I miss any step?
Thanks,
Ser
I think your car only has 2 O2 sensors. If that is correct then you need to have them installed in the pipes so they can read the air/fuel mixture & adjust as needed.
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Old 01-15-2014, 01:29 PM   #17
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^^^^^ What BY says... ^^^^^
Ser,
If you are running ROW specs (which you are in GIB), you need to fit the O2 sensors into the pipes. I bought the Che cat delete pipes (Deluboz Parts) and had to weld in 2 x stub-ins for the sensors...
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Old 01-16-2014, 01:11 AM   #18
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Thanks a lot guys, the car is ROW ecu.
If I leave secondary sensors disconnected, will A/F mix work as normal, just showing CEL, no other side effects?
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Old 01-16-2014, 04:06 AM   #19
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The Fab Speed pipes I bought has a front and rear bung for your O2 sensors. I had to plug both on my pipes since only the forward cats have sensors.
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Old 01-16-2014, 04:09 AM   #20
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Quote:
Originally Posted by notech View Post
Thanks a lot guys, the car is ROW ecu.
If I leave secondary sensors disconnected, will A/F mix work as normal, just showing CEL, no other side effects?
The feedback from those sensors is not just FYI to the engine, it does change operating conditions.
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