Euro cat/section 1 owners need to pick your brain

[nextelbuddy]

So this is going to be an odd one.

On my s54 I had a CSL air box with stock US catted manifolds. I purchased a set of Euro catless headers and removed my stock section 1 and installed a dual resonated section One made from two resonated section 1 pipes coupled along with a stock us section 2 and a CSL section 3

I then decided to purchase a set of European cats or European section 1 from the gentleman that sells them on here from Europe.

I got them installed, and noticed immediately that the tone was very off and different when the engine was cold. It almost sounded like an exhaust leak but there was no exhaust leak I got under the car Nothing was leaking, Making a hissing noise, No pulsating noise or soot anywhere.


When you sit inside the car on a cold start, right underneath the floorboard where the front seats are where the Euro cats are it almost sounds like a growl and it sounds like that even when you're driving until everything warms up and then once things warm up it gets a lot quieter. Almost like an exhaust leak where when things heat up tolerances get tighter

I removed the Euro section 1 put the dual resonated section one back on and installed a dinan section 3 but quickly found out that I don't like that. It's too loud too much drone so I reinstalled the Euro section one again and the CSL section 3.

I made sure to install the section 2 and section 1 together as one piece out of the car used good gaskets got all of the nuts and bolts tight and snug between section 1 and section 2 use new donut gaskets at the header connection

And started the car and cold start sounded better but when I drive it just sounds loud/growly when it's cold. Almost like the cats need to heat up for something and then once the cats heat up it gets quiet


Trying to see what the experience is with other people that upgraded to Euro section 1 cats and if they got a change in tone or if it got louder or anything like that

I'm also curious that if you have a stock E46 M3 with a us cats and stock everything else and the only thing you do is upgrade to the catless European manifolds and the European section one with the cats... Will it be the same tone and exhaust sound or decibel level or will it actually be noticeably louder?

For some reason in my head, I would imagine that it would be louder because you're moving the cats from near the cylinder head down to underneath the floorboard

Sorry if this sounds weird. I've never actually had catalytic converters underneath the car on e46. On my turbo car I went from us cat manifolds to Turbo with cat delete so on this s54 wagon, putting the cats under the floorboard is a first for me

[HoDoo]

nextelbuddy
My car is currently in stock condition with the US manifold (including cats) and the stock US Section 1.
I’m planning to switch to a Euro manifold and Euro Section 1 soon.
I’ll share my experience after the installation.

[Maxhouse97]

In the process of buying a euro section 1 plus euro headers, have a Dinan muffler. Interested to hear other experiences. Will be a while before I can get them on.

[174bpm]

My setup is Megan headers, Euro section 1, OE section 2, Dinan section 3. I didn't notice any growl or increase of exhaust sound/note. However I did step down in loudness from an El Diablo to the Dinan. Still, exhaust note is basically the same from startup to warmup now. Have you inspected the cats with section 1 off the car? My only theory here now is that maybe they have gotten slightly loose and expand on warmup.

[nextelbuddy]

QUOTE=174bpm;n296412]My setup is Megan headers, Euro section 1, OE section 2, Dinan section 3. I didn't notice any growl or increase of exhaust sound/note. However I did step down in loudness from an El Diablo to the Dinan. Still, exhaust note is basically the same from startup to warmup now. Have you inspected the cats with section 1 off the car? My only theory here now is that maybe they have gotten slightly loose and expand on warmup. [/QUOTE]

Is my theory that the catalytic converters themselves were maybe loose or dislodged and expanding when heated up

Supposedly these catalytic converters had 34,000 mi on them. Just why I got them

Only way to test the theory is to get another Euro section 1 and swap it out just to see if it does the same thing

I did look at the catalyst honeycomb material when the section 1 was off and they looked fine. I have pictures of bank one and bank two. They don't look odd broken. No weird colors. They don't look rotated out of the way or anything like that

[maupineda]

My z4m also sounds as if there was a leak when cold, it goes away after warming up. I assume it is the enrichment for cold start. My cats are not OE, but aftermarket.

when I had cold start disabled, it did not do that.

[DJAM3]

I went from stock exhaust to Fabspeed headers and euro section 1 on my first car. I didn't notice any exhaust leak type sound and the tone was slightly louder and deeper. Cold start and the SAP was deleted.

[Cubieman]

I don't remember any such sound running Euro headers/cats.
Just wish I would have kept those fucking things, sounded better than my current setup and I have maybe 10hp to show for it, yay.

[lemoose]

Have you checked the hangers (#8)

[nextelbuddy]

Have you checked the hangers (#8)

Check them for? If they are loose? missing?

[Slideways]

Do you have a sound clip?

With Euro cats, you will hear a bit more metallic rasp during the first few minutes while the engine is warming up. That becomes less as the engine gets to operating temperature.

Unless the shields surrounding the cats have a broken weld or there is crack under the shield causing an exhaust leak, the exhaust note should be similar to stock.

[lemoose]

Check them for? If they are loose? missing?

Either could produce the same symptom but most likely just loose from dry rot. If you give your exhaust tips a good and quick downward tip and on the rebound you hear a clunk that would also help to confirm- but if you get under there it should be painfully obvious visually.

[HoDoo]

I finally swapped the headers and Section 1 on my car to full Euro-spec!
I successfully installed Euro headers and Euro Section 1, and reflashed the DME to version 1501 with JAPAN spec.
Here’s my experience so far:

---

1. Cold start is much more stable

• With the US setup, the RPM was higher and noisier during cold starts.
  But with the Euro spec, the idle stabilizes much quicker and feels smoother.
• There were no strange noises during cold start (like an exhaust leak)

---

2. The high-pitched whistling sound at certain RPMs is completely gone

• If you watch videos of stock US-spec exhausts on YouTube,
  you’ll notice that almost all of them make this whistling sound during startup. That’s no longer there.

---

3. The artificial raspy sound from the single resonator in Section 1 is gone

• Now the exhaust note is a bit louder overall, but in a good way.
  It sounds cleaner and more metallic, like the pure sound of the exhaust itself.
  I believe the US version’s manifold cats muffled this sound,
  so they probably added one resonator in Section 1 to artificially boost the rasp. That’s gone now.
• Personally, I used to enjoy that aggressive metallic raspy sound that came from the old Section 1 setup, so I do kind of miss it.

---

4. Torque feels noticeably better between 5,000 and 8,000 RPM

• Maybe it’s a placebo, but honestly, it feels like torque has increased in that range.
  Even if peak torque is the same, I suspect the torque curve has shifted and improved.

---

The low-speed exhaust tone while cruising through underground parking lots now sounds deeper and more aggressive,
and I’m absolutely loving it!

[LSB4Me]

My CSL headers and euro cats sound completely as expected. You should chase this down.

Could be heat shields. Could be hangers. Could be header seals at the manifold.

Weird exhaust noises are pretty easy to troubleshoot. You might want to put it in the air while running and check for issues.

Cubieman is right. Oem euro headers + cats and done.