Secondary Cat Removal Anyone?

[3002 tii]

I'm all about being green friendly so plan on keeping the primary cats (by the headers) but from what I've read, the secondary cats aren't as important (and euro cars don't have them)?

If so, has anyone here removed them, ie run a straight pipe? Are there gains to be expected? Increase in drone / smell?

Whether you a 2.5i or /m, I'm sure the answer is the same for all platforms so everyone should feel free to chime in. TIA.

[Incompatible]

Here in "Kalifornia" we do not have that as a legal option.

[esqu1re]

Originally Posted by Dubbedown

I'm all about being green friendly so plan on keeping the primary cats (by the headers) but from what I've read, the secondary cats aren't as important (and euro cars don't have them)?

If so, has anyone here removed them, ie run a straight pipe? Are there gains to be expected? Increase in drone / smell?

Whether you a 2.5i or /m, I'm sure the answer is the same for all platforms so everyone should feel free to chime in. TIA.

I thought the europeans didn't have the ones on the headers. You might have it reversed (or i do).

[pokeybritches]

The Euro cars have larger cats in section 1 of the exhaust to make up for the lack of cats in the headers (correct me if I'm wrong). If you're going to be illegal, be illegal with catless headers. That's where a well-designed and less restrictive system is most critical, and therefore we see the largest gains.

I'm looking at possibly getting M54 AA headers for ~$1200, but I have to ensure they fit first. I'm not sure who makes N52 headers. I would only start looking at a catless section 1 f there aren't any on the market.

[Starscream]

If there is no sensors back there (and from memory I don't think there is)
Then there should be no problem running catless,

i think both euro and US N54 engines use cats in the headers,

[3002 tii]

Originally Posted by pokeybritches

The Euro cars have larger cats in section 1 of the exhaust to make up for the lack of cats in the headers (correct me if I'm wrong). If you're going to be illegal, be illegal with catless headers. That's where a well-designed and less restrictive system is most critical, and therefore we see the largest gains.

I'm looking at possibly getting M54 AA headers for ~$1200, but I have to ensure they fit first. I'm not sure who makes N52 headers. I would only start looking at a catless section 1 f there aren't any on the market.

Problem with catless headers is that you run into the CEL problem whereas secondary cats don't give the error light. Not to mention headers are super expensive ($1600 for n52) whereas a straight pipe by the 2ndary costs far less.

[Incompatible]

Originally Posted by Starscream

If there is no sensors back there (and from memory I don't think there is) Then there should be no problem running catless, i think both euro and US N54 engines use cats in the headers,

True for some states, not for others. If going this route it's best to research what your state regulations are. No sensors on N52 (Z4) secondary cats, sensors only on the primary cats in the exhaust manifold.

Originally Posted by pokeybritches

.... If you're going to be illegal, be illegal with catless headers. That's where a well-designed and less restrictive system is most critical, and therefore we see the largest gains.....

X2

Following the various threads across the forums suggests a negligible increase in horsepower and slight increase in sound. Difficult to tell as this mod is usually performed along with a change/deletion of the muffler.

[pokeybritches]

Originally Posted by Dubbedown

Problem with catless headers is that you run into the CEL problem whereas secondary cats don't give the error light. Not to mention headers are super expensive ($1600 for n52) whereas a straight pipe by the 2ndary costs far less.

You can try relocating your secondary O2 sensor bungs to post-section 1 cats if you get catless headers, or develop your own simulator if you have the tools (OBDII code reader/reset is a necessity). I haven't researched the N52 engines enough to know if this will fix the CEL, but on the S54 it should. On the M54, apparently it still throws a code unless the secondary cats are swapped for some aftermarket.

I would try doing a forum search for some E9x 330i/Z4 owners that have tried relocating the O2 sensor bungs with the stock section 1 and aftermarket catless headers. If you don't net any info, then go with a section 1 cat delete. The problem with the section 1 cat delete is that it's illegal and you won't get around any visual inspections, and the HP gains aren't as great as a header swap (which you can sneak around certain inspections). The only perk is that your CEL doesn't illuminate.

In my home county in TN, the inspection is two parts. The first consists of plugging into the OBDII port and checking the electronics (ensures the O2 sensors aren't turned off with a tune, and there is no CEL), and then a visual inspection of the cats with a handheld mirror on a pole. I don't know what kind of inspections NJ has, but if it is similar to TN I have a feeling the car would fail with the section 1 cats removed.

I think there's more hp to be had with a header swap, and you might be able to get around certain inspections. With a section 1 cat delete, you won't throw a CEL, but you won't get past a visual inspection in most states.

[3002 tii]

Originally Posted by pokeybritches

You can try relocating your secondary O2 sensor bungs to post-section 1 cats if you get catless headers, or develop your own simulator if you have the tools (OBDII code reader/reset is a necessity). I haven't researched the N52 engines enough to know if this will fix the CEL, but on the S54 it should. On the M54, apparently it still throws a code unless the secondary cats are swapped for some aftermarket.

I would try doing a forum search for some E9x 330i/Z4 owners that have tried relocating the O2 sensor bungs with the stock section 1 and aftermarket catless headers. If you don't net any info, then go with a section 1 cat delete. The problem with the section 1 cat delete is that it's illegal and you won't get around any visual inspections, and the HP gains aren't as great as a header swap (which you can sneak around certain inspections). The only perk is that your CEL doesn't illuminate.

In my home county in TN, the inspection is two parts. The first consists of plugging into the OBDII port and checking the electronics (ensures the O2 sensors aren't turned off with a tune, and there is no CEL), and then a visual inspection of the cats with a handheld mirror on a pole. I don't know what kind of inspections NJ has, but if it is similar to TN I have a feeling the car would fail with the section 1 cats removed.

I think there's more hp to be had with a header swap, and you might be able to get around certain inspections. With a section 1 cat delete, you won't throw a CEL, but you won't get past a visual inspection in most states.

thanks for the info, btw i'm not debating whether catless headers is more gains than 2ndary cat delete. i know for a fact you'll see more gains with aftermarket headers, i was only considering the 2ndary due to its ease/cost.

[wrh3]

I had a friend that did this when he picked up his 2006 Z4M, no issues but he couldn't really tell a difference.

[inTgr8r]

Originally Posted by Dubbedown

thanks for the info, btw i'm not debating whether catless headers is more gains than 2ndary cat delete. i know for a fact you'll see more gains with aftermarket headers, i was only considering the 2ndary due to its ease/cost.

I noticed the topic got slightly derailed.

Removing the section 1 CATs, should yield better flow.
I don't know of anyone that has attempted this and done any dyno testing to prove gains though.

I would think you will also get more of a rasp sound to the exhaust.

[3002 tii]

Originally Posted by inTgr8r

I noticed the topic got slightly derailed.

Removing the section 1 CATs, should yield better flow.
I don't know of anyone that has attempted this and done any dyno testing to prove gains though.

I would think you will also get more of a rasp sound to the exhaust.

thanks for getting this back on topic, seems like 2ndary cat deletes is a pretty common mod for n54 guys but not so much on n/a (probably b/c there are few vendors who provide the replacement pipes for 135/335 owners).

i do know one guy who did on his n52 but he never dyno'd before/after and also did other major exhaust work at the same time so it's hard to isolate just on this mod by itself. his best guess was few hp at most...

[3002 tii]

I see this thread gets a decent number of hits (forum notifications) so thought I'd update readers. Since the original posting over 6 years ago, there have been a lot of developments for the n52, including catless headers. I ultimately chose to go with Supersprint headers, 3" custom catback with 100 cell hfc. And while the HFC won't get around emissions, one option is to relocate and extend the rear o2's as per Pokey's recommendation. However I didn't want to go through that effort only to find out 100 cell wouldn't be enough to pass smog, so I decided to go with o2 simulators from VRSF.

See my thread here.

[Vanne]

Euro cars only have cats in the section 1. (so thats AFTER) the headers. (our cats in the section 1 are about 1.5 times the size of your cats (in the same place). not sure if euros came with 400 or 200CELL's . Ill take some pics when i go grab my car


Pulled mine, hoping the smell aint too bad, hoping for no CEL, picking it up soon i hope.. So for a euro car , this will be completely catt-less with a SS section 1. Oh, i probably didn't mention we don't have any /real/ smog checks here..

[3002 tii]

Originally Posted by Vanne

Euro cars only have cats in the section 1. (so thats AFTER) the headers. (our cats in the section 1 are about 1.5 times the size of your cats (in the same place). not sure if euros came with 400 or 200CELL's . Ill take some pics when i go grab my car


Pulled mine, hoping the smell aint too bad, hoping for no CEL, picking it up soon i hope.. So for a euro car , this will be completely catt-less with a SS section 1. Oh, i probably didn't mention we don't have any /real/ smog checks here..

That's a lot of hoping lol. But *fingers crossed*

The odor's worst when you're sitting idle at a light (worse for the car behind you I presume). Not sure how euro software is different but I don't see why a CEL wouldn't appear, else how would someone know if their section 1 cats failed or not?

[Vanne]

Originally Posted by 3002 tii

That's a lot of hoping lol. But *fingers crossed*

The odor's worst when you're sitting idle at a light (worse for the car behind you I presume). Not sure how euro software is different but I don't see why a CEL wouldn't appear, else how would someone know if their section 1 cats failed or not?

Lol yeah, haha..

Not running stock software, but yeah really hoping not to loose bottom end power for a little bit extra up top.




SS section 1. needs to be run a bit to remove some carbon.


Catt-less.