DIY: OEM x-pipe secondary cat removal/gut

Thanks for the write up!

MikeE92M3 wrote

I had my exhaust shop close to me take out the secondary cats and replace it with pipes with a small "crush" at the end so it would fit in the x pipe.

It does NOT drone, and it actually sounds very very good. Has more of a rumble and you can definitely hear its presence under load. I don't feel significant power gains, but it feels more "free."

Just had the same exact thing done to my car. Sounds really aggressive with the oem mod!

I did this today, Eric thank you for sharing this info!

has anyone got proven gains with doing this ?? is it for sure not gonna cause back pressure by removing that and not just replacing with a straight pipe

beemerboy305 wrote

has anyone got proven gains with doing this ?? is it for sure not gonna cause back pressure by removing that and not just replacing with a straight pipe

No gains. This is just for sound.

OP: First awesome write-up!

I plan to do the same thing and wanted to ask you a few things:

a) What rear muffler are you running?

b) IF stock how much increased sound did you get by removing the secondary cats and do you think you gained any power?

c) I'm debating right now to gut the cats or just cut them out since I'm not too worried about the visual part. Would the final effect be the same?

d) If you are running an aftermarket rear muffler, what brand and how's your sound before and after gutting the secondary cats?


Kudos great job, I want to try this before spending $2k+ on a pipe as I prefer to dump that into my Brembo's

erics02wrx wrote

I have the UUC / Corsa exhaust and I was afraid of the same thing (being to loud) but it was barely noticeable. Its a little louder from the outside of the car but on the inside its maybe 5% louder, if that. I love it!

One more question, have you thought of removing the OEM resonators as well or would that trip the CEL? I guess I'll do one at a time to get the sound I want but wondering if anyone has removed the secondary cats + resonators on a stock X-pipe?

s4play wrote

OP: First awesome write-up!

I plan to do the same thing and wanted to ask you a few things:

a) What rear muffler are you running?

b) IF stock how much increased sound did you get by removing the secondary cats and do you think you gained any power?

c) I'm debating right now to gut the cats or just cut them out since I'm not too worried about the visual part. Would the final effect be the same?

d) If you are running an aftermarket rear muffler, what brand and how's your sound before and after gutting the secondary cats?


Kudos great job, I want to try this before spending $2k+ on a pipe as I prefer to dump that into my Brembo's

I am not the OP obviously, but the 2ndary cats are essentially HFC (200 cell I think). So removing them, you will gain some power, but probably not that much. I am not sure on sound...

If you don't want to spend $2k+ on a pipe, may I suggest Test Pipes to remove the primary? ~$400 plus some way of removing CEL if that annoys you (couple different ways of doing this with the Tune being the most expensive.)

Just point the thought in your head if you didn't already have it!!

thanks!

I'm getting my work done tomorrow and will report back

what if i did this mod + my oem exhaust mod?

would it be way too loud?

Kunman wrote

what if i did this mod + my oem exhaust mod?

would it be way too loud?

I think this mod would be a great addition to the OEM exhaust mod.....our cars are way to quiet in stock form, so actually being able to hear this amazing V8 sound come from a completely stock looking exhaust is really cool! By doing this mod in combination with your OEM exhaust mod, it will probably make the car sound more like an exotic. I have now lived with this mod for a few years and still never regret doing it, in fact it's still one of my most favorite mods that I've done.

erics02wrx wrote

I think this mod would be a great addition to the OEM exhaust mod.....our cars are way to quiet in stock form, so actually being able to hear this amazing V8 sound come from a completely stock looking exhaust is really cool! By doing this mod in combination with your OEM exhaust mod, it will probably make the car sound more like an exotic. I have now lived with this mod for a few years and still never regret doing it, in fact it's still one of my most favorite mods that I've done.

I just switched back to my oem x pipe and an MPE…I have a feeling this would make the MPE sound even better as it sound fantastic but just isn't loud enough for me.

can you just get by with simply wire up o2 simulator? I know old e46 I had worked .. but I havent tried or anything on new one..

happos2 wrote

I am not the OP obviously, but the 2ndary cats are essentially HFC (200 cell I think). So removing them, you will gain some power, but probably not that much. I am not sure on sound...

If you don't want to spend $2k+ on a pipe, may I suggest Test Pipes to remove the primary? ~$400 plus some way of removing CEL if that annoys you (couple different ways of doing this with the Tune being the most expensive.)

Just point the thought in your head if you didn't already have it!!

yellow munson wrote

can you just get by with simply wire up o2 simulator? I know old e46 I had worked .. but I havent tried or anything on new one..

I am not too familiar with this. There is something that Burger Tuning makes I think (I feel like I read that somewhere on this forum) which would essentially be a simulator. People have also used spacers to pull out the O2 sensor with different success rates. And finally one of the vendors here makes an O2 sensor that is surrounded by a cat (call it a mini cat or something like that) which is plug and play as well.

All that being said, if you are eliminating the primary cats, the best is to get a tune and extract the extra power and get the other benefits of the tune.

i know this was from 3 years ago but i still wanna ask...ive heard that deleting the secondary cats will cause u to fail emissions im in nj and pretty sure they just do a OBD port test but not sure...is this true because i want to do this also if i get secondary cat delete pipes will that cause a cel

jamesching wrote

i know this was from 3 years ago but i still wanna ask...ive heard that deleting the secondary cats will cause u to fail emissions im in nj and pretty sure they just do a OBD port test but not sure...is this true because i want to do this also if i get secondary cat delete pipes will that cause a cel

the 2nd cats are over kill. they do not cause a CEL and you should still pass a emission test with them gone!

Sucks that there isn't much of HP gains.

nice! might try this but just replace with straight pipes

hawaiiracer1 wrote

I did this mod over the weekend and it sounds freaking awesome , And All I did was an OEM exhaust mod and gutted the second cat , thanks for the ideal never thought of it

Which OEM exhaust mod did you do? 2-pipe, 2.5pipe, 4pipe or bypass? Did you do the mods yourself?

m3alabama wrote  

if you are comfortable hacking up the exhaust than you should go a step further. Cut out the secondaries and cut out the primaries. Put the secondaries welded in to replace primaries and put it all back together. This should be enough to easily avoid the CEL and give you essentially a HFC setup

karussell wrote

I was just thinking this since the secondary cats are 200 cells. i bet a good muffler shop could make quick work out of this. would it be much louder?

A few years later and no one else seemed to notice this. Has anyone done this? It seems like it would require little in labor and would put the stock HFC in the right place and save a lot of cash that could be spent elsewhere.

Freiheit wrote

m3alabama wrote  

if you are comfortable hacking up the exhaust than you should go a step further. Cut out the secondaries and cut out the primaries. Put the secondaries welded in to replace primaries and put it all back together. This should be enough to easily avoid the CEL and give you essentially a HFC setup

karussell wrote

I was just thinking this since the secondary cats are 200 cells. i bet a good muffler shop could make quick work out of this. would it be much louder?

A few years later and no one else seemed to notice this. Has anyone done this? It seems like it would require little in labor and would put the stock HFC in the right place and save a lot of cash that could be spent elsewhere.

hmm... would it be enough for a stage 2 tune also?