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Old 08-05-2018, 03:14 PM   #1
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Almost done

my replacement 2.5L engine is in, transmission mounted and half shafts in. Went to replace the exhaust system and discovered the cat on the left side has several holes (and others previously spot welded), and the "guts" of the cat fell out. With that said, living in a non-smog state I am planning on going with the delete pipes. I do not know which is the better option:
Resonated - https://www.ebay.com/i/122412283693?chn=ps

or straignt - https://www.ebay.com/itm/Porsche-Boxster-97-99-2-5L-986-Secondary-Test-Pipe-DeCat-Pipe-Cat-Delete-Pipes/123063021275?
hash=item1ca720aedb%3Ag%3ABLQAAOSwemVax9dC&_sacat=0&_nkw=+Porsche+Boxster+2.5L+97+98+99+Test+Pipe+Cat+ Delete+Pipes+&_from=R40&rt=nc&_trksid=m570.l1313

Looking for advise. I do not want a car so loud I can't talk to my wife, however...
What do I need to do to eliminate the CEL for O2 sensors if I go with either option.
Please adivse. I just want to get the car on the road so I can enjoy some top-down driving.

Fred in Florida

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Old 08-05-2018, 06:22 PM   #2
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Only your front O2 sensors are used for the CEL so as long as you leave them in place you shouldn't have a problem.

Best of luck!
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Old 08-05-2018, 07:59 PM   #3
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Quote:
Originally Posted by dghii View Post
Only your front O2 sensors are used for the CEL so as long as you leave them in place you shouldn't have a problem.

Best of luck!
Negative...

The rear post cat O2 sensors monitor the health of the cats. If the cats are gone, you'll get a code. If the sensors are gone, you'll get a code.
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Old 08-05-2018, 09:13 PM   #4
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ROW tune.....
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Old 08-05-2018, 09:23 PM   #5
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A 2.5L car (97-99) only has one set of cats (in the mid-pipe) and one set of O2 sensors. The cats can be removed using test pipes and the test pipe should have a bung to mount the O2 sensors. The car will pollute more without the cat's but you shouldn't get any CEL's.

Here is a photo from engine back: On the left of the photo is the stock exhaust manifold, stock mid-pipe with the cat, and the Top Speed Pro 1 muffler. On the right of the photo is the stock exhaust manifold, cat delete pipes with O2 sensor, and Top Speed Pro 1 muffler.

Removing the cat's definitely increases the sound level. With no cat's and the Top Speed muffler, I wear earplugs. With no cat's and the stock muffler, the car is louder but might be livable. Everyone's noise preference/tolerance is different so its hard to say if this will be acceptable. YMMV.

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Last edited by thstone; 08-05-2018 at 09:27 PM.
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Old 08-05-2018, 09:28 PM   #6
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I'm sure Tom's post was just a typo, but...

2.5 cars have 2 sets of O2 sensors (4 total), pre and post cat, same as all US 986 models.
The 2.5 only has one set of cats...




OP: best solution, in my opinion, is to replace the cats. If you want more sound, replace or modify the muffler with a bypass.

Last edited by particlewave; 08-06-2018 at 10:28 AM.
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Old 08-07-2018, 05:24 AM   #7
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I NEED HELP! Going with the Circuit Werks cat delete pipes, however, what is the difference between resonated and non-resonated pipes? Will I be able to carry on a conversation with my wife while driving with either pipes? I want to get the car back on the road and this is the last hurdle I have to overcome. Help a guy get his Porsche back on the road!!! PLEASE... I want to have at least on summer top-down driving story to tell.
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Old 08-07-2018, 06:33 AM   #8
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Easy, now, take a deep breath

About a month ago bought and installed a set of the Circuit Werks "resonator" mid pipes. Pictures below.

I don't think that the "resonator" portion of these pipes does all that much, as you can see that it is a straight-thru design. So there is very little flow restriction offered by the "resonators". Which also means that there's not a whole lot of acoustical benefit to be offered by them, either.

Without doing a back-to-back A vs. B comparison between these pipes and their straight version, there's no way to note if there is a genuine acoustical difference between them. I simply selected this option as I wanted to try to see if I could take a bit of an edge off of the resulting unrestricted sound.

If you are using an OEM muffler, my vote would be to use the straight pipe design as these stock mufflers seem to have more than enough restriction for two cars. But if you are going to an aftermarket muffler (as I did), then I would vote for using the "resonators". Can't hurt.

DM
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Old 08-07-2018, 06:37 AM   #9
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Oops, forgot the pics:


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Old 08-07-2018, 06:45 AM   #10
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One more related thing.

Note that the manifold exit flange bolt pattern differs between the early and the later models. The pipes themselves appear to be identical - only the bolt flange patterns differ, for no obvious reason.

Point being that you will need to ensure that you buy the correct CW mid-pipes which match your manifolds.

Hope this helps - DM

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Old 08-07-2018, 11:59 AM   #11
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Quote:
Originally Posted by Dave80GTSi View Post
Easy, now, take a deep breath

About a month ago bought and installed a set of the Circuit Werks "resonator" mid pipes. Pictures below.

I don't think that the "resonator" portion of these pipes does all that much, as you can see that it is a straight-thru design. So there is very little flow restriction offered by the "resonators". Which also means that there's not a whole lot of acoustical benefit to be offered by them, either.

Without doing a back-to-back A vs. B comparison between these pipes and their straight version, there's no way to note if there is a genuine acoustical difference between them. I simply selected this option as I wanted to try to see if I could take a bit of an edge off of the resulting unrestricted sound.

If you are using an OEM muffler, my vote would be to use the straight pipe design as these stock mufflers seem to have more than enough restriction for two cars. But if you are going to an aftermarket muffler (as I did), then I would vote for using the "resonators". Can't hurt.

DM
Deep breath taken. I have a line on a set of cats, so I will stick to using OEM parts. Thanks For the help and advise. One step closer to that top down summer drive. Good thing summer lasts well into October here in FL!

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