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Old 02-18-2010, 06:19 PM   #1
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Questions about headers and bypass

So Im thinking of getting an exhaust and thought while Im at it get headers. Been doing alot of research and Im kinda confused about the cats. I hear that the headers are attached to the cats and if you remove them the CEL comes on. So If I change the headers would i get CEL ? and would it smell funny? I live in California so I need to be able to pass smog so Im not sure if changing the headers would affect it or not.

Also I have been seeing videos and hearing people talk about the secondary Bypass, such as the one fabspeed sells. Can someone explain exactly what that is and why people get it? does it just by pass the secondary cats? do you keep stock headers get a bypass and exhaust to prevent CEL or what.


lastly what type of headers would you recomend? the ones on ebay all seem to be the same and rebranded with some selling for more. Theres also an NHP one with cats attached to it, which is $1K. Ive heard they are all the same so what do you guys think.

sorry for sounding ignorant on this. Im just trying to be sure before I know which direction to go with my next project.

Thanks

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Old 02-18-2010, 06:57 PM   #2
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I don't have headers, and I'm no expert, but I've read about it a lot here...

this is what I BELIEVE to be true...

on YOUR car, a 2001 model, you have cats IN your headers and secondary cats in the next set of pipes that are in between the headers and muffler.

you can remove the secondary cats and likely still pass a CA sniffer test. techincally you would flunk the visual, asyou modified the exhaust system and removed cats, but the reality is probably NO smog tech knows that boxsters have TWO sets of cats, and if they see the first set, they are happy and pass you.

if you removed the front and secondary set,, you would fail.

i dont' know what would happen if you took of the fronts, but left hte secondaries.

the 97-99 cars had only cats in the headers...and there is sometimes confusion because what works on a 97-99 is not what is true for 2000 and on.

I believe the most common setup on a car like YOURS is to retain teh stock headers/cats and just put on a muffler and then maybe add the secondary cat bypass pipes.

another unforutnate thing is that nothign on these cars is cheap, and any reputable company seling this stuff wants an arm and a leg for it. for example, the NHP muffler and their bypass pipes are about $1200. it probably sounds cool and likely yuou'll get no ral power gain out of it. $1200 is a lot to sound cool.

my next mod will likely be a pulley...as you can get that for about $300 and you will actually get gains you can feel...
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Old 02-18-2010, 07:38 PM   #3
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Quote:
Originally Posted by 23109VC

i dont' know what would happen if you took of the fronts, but left hte secondaries.
The biggest problem you would now face is that you have a set of O2 sensors BEFORE the primary cats (the ones integrated in the headers) and another set BEHIND the primary cats.

So here's what happens:
The after markets headers have usually only one set of holes for the O2 sensors so your second set would dangle in the air. To make things worse the DME will be very confused as both sets of O2 sensors now read the same values (and the DME usually expects the air before it goes through the cats to be dirtier than after). So if you just leave t like this you will have a check engine light and probably poor performance. But there are ways around this, do some search on the forums.

But long story short: You do not run into these issues if you leave the original headers on and replace the secondary cats with a bypass pipe, and this is also mechanically less challenging (there's a bunch of guys who had serious trouble with the studs with which the headers are attached to the motor)
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Old 02-18-2010, 08:55 PM   #4
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So technically I can play it safe keep the stock headers and get the bypass for 500 bucks and a muffler and get no CEL and still get a nice sound. how much of a difference in sound or power would headers make? I feel like the headers are all the same and the ones that are not are way to expensive and the power claims seem exaggerated.
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Old 02-19-2010, 08:00 AM   #5
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This is interesting reading.

My 97' pulled a CEL for failing cat (P0430). I was going to purchase both, but didn't realize they have 4 cats? I'd have to stick my head under there again, but I think I've seen only the 2 cats with an O2 before and after each cat.

Am I wrong here? I would think cat bypass pipes would throw CEL's all over.
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Old 02-19-2010, 08:31 AM   #6
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My 3.6 is catless and at present the after cat O2 sensors are clamped underneath the car. Surprisingly it does not throw codes as often as you would think. I hate having the CEL lit so I have found a $10 fix for this. Fortunately a spark plug and an O2 sensor have the same threads. I went to Autozone and bought a $4 set of anti-foul spark plug adapters. I then went to the hardware store and bought a set of brass caps to fit on the end where the hole is. The end of the O2 sensor is a tad bigger than the bottom of the anti-foul adapter because it tapers where the second set of threads is on the bottom. A few seconds with a drill on a drill press to enlarge the area at the bottom of the inside so the O2 sensor will fit inside the adapter. Screw the unit onto the end of the O2 sensor, clear the codes and Bob's your uncle. No more CELs.
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Last edited by landrovered; 02-19-2010 at 08:33 AM.
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Old 02-19-2010, 08:40 AM   #7
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Quote:
Originally Posted by root_werks
This is interesting reading.

My 97' pulled a CEL for failing cat (P0430). I was going to purchase both, but didn't realize they have 4 cats? I'd have to stick my head under there again, but I think I've seen only the 2 cats with an O2 before and after each cat.

Am I wrong here? I would think cat bypass pipes would throw CEL's all over.
Your '97 only has 2 cats total. One on the left and one on the right.

The cats are located in between the headers (a/k/a exhaust manifold if it's stock) and the rear muffler.

The '97 has a total of 4 O2 sensors, and they are located on the cat pipe, just before and just after the cat.

Here is a photo of the right side stock header (exhaust manifold) on a '97:





Here is a photo of a Billy Boat header installed on the right side:





Here is a photo before the muffler installation, showing the headers installed with the stock cats for a '97. The red arrows point to the O2 sensors at the rear of the cats. The front O2 sensors are not visible here, but are at the front of the cats:





Do not take the caution about the exhaust manifold bolt heads snapping off when trying to remove the stock exhaust manifold from the head lightly:

http://www.ppbb.com/phorum/read.php?19,1552140,1552140#msg-1552140

Regards, Maurice.

Last edited by schoir; 02-19-2010 at 08:53 AM.
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Old 02-19-2010, 09:21 AM   #8
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Great pictures thank you! That's pretty much what I thought after doing a little more reading up on things. Actually makes putting headers on the 2.5 an easier task than 2.7's and up I guess?

This is turning into a good informational thread on the differences between the early and later Boxsters.
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Old 02-19-2010, 09:52 AM   #9
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Quote:
Originally Posted by Stunin_Stud
So technically I can play it safe keep the stock headers and get the bypass for 500 bucks and a muffler and get no CEL and still get a nice sound. how much of a difference in sound or power would headers make? I feel like the headers are all the same and the ones that are not are way to expensive and the power claims seem exaggerated.
Can't talk about the headers, but here's the breakdown for exhaust and bypass:
I have a modded exhaust (no droning and great sound) and added the bypass pipes later
I would say that the exhaust makes 90% of the better sound and the bypass pipes 10% (when reved over 3,500 RPM).

I see you're in San Jose, I work in Santa Clara, let me know if you want to listen to my setup

Edit: Reading your signature I'd guess we already met before
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Old 02-19-2010, 09:53 AM   #10
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what about the fabled (perhaps 100% true) notion that these cars need back pressure? I was looking at sport cats and asking around, one guy said he wished he has purchased the 200 cell vs the 100 cell for the back pressure, what't the experience of the header owners??
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Old 02-19-2010, 10:19 AM   #11
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Thanks I may get in touch with you to check out your car. Im currently in the caribbean.
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Old 02-19-2010, 10:43 AM   #12
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Quote:
Originally Posted by landrovered
My 3.6 is catless and at present the after cat O2 sensors are clamped underneath the car. Surprisingly it does not throw codes as often as you would think. I hate having the CEL lit so I have found a $10 fix for this. Fortunately a spark plug and an O2 sensor have the same threads. I went to Autozone and bought a $4 set of anti-foul spark plug adapters. I then went to the hardware store and bought a set of brass caps to fit on the end where the hole is. The end of the O2 sensor is a tad bigger than the bottom of the anti-foul adapter because it tapers where the second set of threads is on the bottom. A few seconds with a drill on a drill press to enlarge the area at the bottom of the inside so the O2 sensor will fit inside the adapter. Screw the unit onto the end of the O2 sensor, clear the codes and Bob's your uncle. No more CELs.
I understood everything you just said above. SOOoooooooo, if I wanted to let's say, get some bypass pipes instead of some new cats (keeping the old ones of course...on the shelf), sounds like this little trick does the job? Of course, you have a 3.6 with I'm sure a mod'd ECU and mine is a stock 2.5. Hmmm.
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Old 02-19-2010, 10:47 AM   #13
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An O2 sensor is an O2 sensor, it does not care whether it is a 2.5 or a 3.6 in fact I am pretty sure that the ones on there are from the old engine anyway.
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Old 02-19-2010, 10:48 AM   #14
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Originally Posted by Stunin_Stud
Thanks I may get in touch with you to check out your car. Im currently in the caribbean.
Cool, which island?
I've been to Saba a lot in the last 3 years (like 20 times or so)
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Old 02-19-2010, 11:11 AM   #15
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Question about the cat bypass pipes

Was thinking about doing the Fabspeed cat bypass pipes on my 01, which has both primary and secondary set of cats. Wondering though- if I get rid of the cats in the rear section and replace with the Fabspeed Cat Bypass pipes, since there are a set of 02 sensors in the rear section as well, wouldn't that set off a CEL light if removed?
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Old 02-19-2010, 11:19 AM   #16
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Originally Posted by Boxtaboy
Was thinking about doing the Fabspeed cat bypass pipes on my 01, which has both primary and secondary set of cats. Wondering though- if I get rid of the cats in the rear section and replace with the Fabspeed Cat Bypass pipes, since there are a set of 02 sensors in the rear section as well, wouldn't that set off a CEL light if removed?
take a look at where your O2 sensors are and where the cats are on your car and then you have your answer...
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Old 02-19-2010, 11:29 AM   #17
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Originally Posted by Boxtaboy
Was thinking about doing the Fabspeed cat bypass pipes on my 01, which has both primary and secondary set of cats. Wondering though- if I get rid of the cats in the rear section and replace with the Fabspeed Cat Bypass pipes, since there are a set of 02 sensors in the rear section as well, wouldn't that set off a CEL light if removed?
No it won't set off a CEL if you remove the rear cats and replace with Fabspeed by-pass pipes.

You won't regret your purchase either!!!
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Old 02-19-2010, 11:34 AM   #18
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Ok, thanks guys. I presume the rear 02 sensors are located before the secondary cats, and therefore, do not trigger the CEL when the bypass pipes are installed.
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Old 02-20-2010, 07:29 AM   #19
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Originally Posted by ChrisZang
Cool, which island?
I've been to Saba a lot in the last 3 years (like 20 times or so)

Im in Dominica. Im trying to plan out my projects so when I come back to San Jose I can put everything together at once. I currently have the 2003 euro rear bumper being painted along with center console and speedster humps.
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Old 02-20-2010, 12:22 PM   #20
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I experimented with several different exhaust configurations before choosing the final system for my 3.2 S. I found the following set-up produced the best results in terms of performance and reliability (keeping my vehicle OBD II compliant).
Here's my ditty:

1. A less restrictive, high quality after -market cat back exhaust.
2. By-passing/deleting the secondary cats (they're like having an extra set of thumbs).
3. Headers and cats that stick with the basic principles of the oem design, however, they incorporate longer, equal length primaries that flow into a merge collector, along with lower cell - high flow cats (something on the order of HJS 200 cell).

No need to relocate O2 sensors, make bungs, chase CEL's, reprogram the ECU, or worry about emissions ! Excellent results in terms of improved power and performance. And perhaps equally important - great sound !


Last edited by Johnny Danger; 02-20-2010 at 12:26 PM.
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