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      01-11-2019, 12:45 AM   #1
RTCalifornia
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2nd Cat delete but keeping the look specifically for California

Hi Folks,
just wanted to share a different method for the 2nd cat delete. This method removes the Catalytic core only and should pass the visual inspection especially for California SMOG tests. I was surprise how easy and clean it was.

Background:
The sound of my zcp exhaust is good but wanted it to be a bit louder while maintaining the ability to be quiet when needed. I bought a 2nd set of zcp exhaust from a member in this forum and experimented on it just in case I royally screw things up, I would still have my original to go back to.

The mod:
I notice from day 1 these catalytic were 2 halves welded together with a huge seam tab.

I started with a grinder and ground about 3mm off the seams on both sides. I then cut only the top half of the shell and the Ceramic core literally rolled right out. The core is held in by some heat insulation shield which came off easily too. It took about 3 hours to remove and Tig weld it all back together. Because I had only cut the top half, I did not have to re-align the tubes between the mid section to the flange pipe as everything was still held together. It was all too easy.

Here are some pictures of the process and the comparison between the modified and stock zcp. If you live in California and want to go with the 2nd cat delete, try this method and you shouldn't have to worry about the visual inspection.

The sound now is noticeably louder with the valves open when listening outside the car. BMW did too good of a job keeping the noise shielded when inside the car so the sound while driving is only a tad louder.

1st picture shows the cut revealing the ceramic core and insulation
2nd picture is the completed cuts
3rd the cats completely welded back.
4th close up of the original cat.
5th sizd by side zcp stock vs zcp catless core
6th car on lift
Attached Images
      
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Last edited by RTCalifornia; Yesterday at 02:17 PM. Reason: ASD disabled.
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      01-11-2019, 01:56 AM   #2
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Nice any sound clips before and after?
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      01-11-2019, 02:54 AM   #3
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Great idea and excellent project! The ceramic honeycomb filter looks restrictive AF! I feel for those who insist on pushing a lot of boost with the factory midpipes in place. It kind of reminds me of what happened to this member: https://f80.bimmerpost.com/forums/sh...6&postcount=92
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      01-11-2019, 03:45 AM   #4
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So in Cali they don't use a heat prob to check if u have a functioning cat? Locally here they have a prob that they wave under the car and should go cold hot cold etc
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      01-11-2019, 09:48 AM   #5
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Great idea and execution 👍. I'll be moving to CA this year and really apprehensive of all the regulations. I was hoping to gut the stock primary downpipe cats, v-band a resonator to the stock muffler and have the stock secondary or highflow cats as another option. Would they really use a heat probe ?? Thought it was all just a visual inspection
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      01-11-2019, 12:53 PM   #6
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Beautifully done! Kudos to you for doing this! I kept my stock secondaries after I cut them out and planned to cut them open. Now I don't have to!
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      01-11-2019, 12:59 PM   #7
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That's some surgical level skill with the torch and welding!
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      01-11-2019, 01:15 PM   #8
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Awesome work man.

Can you comment on the effect this has had on the burbles in sport +? Also curious if this has had any impact on drone.
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      01-11-2019, 01:50 PM   #9
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that new CA law will sent him to a referee station. if he was to get cited.

they will measure the exhaust content. I think they will see it's not to spec.

always keep the OEM parts on hand in CA.

I wonder if the ref station can figure out if loaded with BM3 map. you can always run E85 and have a 'cleaner' exhaust. maybe they won't even care since it's sound related.
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      01-11-2019, 08:50 PM   #10
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Clean work! Thanks for sharing!
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      01-12-2019, 01:12 AM   #11
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thank you.

Thanks for all comments.

Just a quick sound/video after 2nd cat core delete.

After listening to the live exhaust sound and hearing it again on video, I can definitely say the sound clip is missing the true bass rumble and feel. Standing behind the car at cold start with valves open, I could really "feel" the sound. Towards the end of the clip, notice how far the car has driven away from the camera and the distinct exhaust sound is still heard.

A special note on the smell:
Absolutely no difference compared to stock. i was expecting to smell some un-burn gas or some rich burn but nothing.

Here is the revised video.

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Last edited by RTCalifornia; Yesterday at 02:18 PM.
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      01-12-2019, 05:03 AM   #12
RTCalifornia
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Quote:
Originally Posted by Tall Tom Cruise View Post
Awesome work man.

Can you comment on the effect this has had on the burbles in sport +? Also curious if this has had any impact on drone.
The burbles are much more pronouced. Its definitely louder with more deep bass. Pops are also louder. I have the valves forced open all the time by default so there is some droning at around 3000 RPM. This is the same as it was before with the 2nd Cat in place. However, after 3500 RPM, the engine growl is very noticeable in the cabin especially if pushing it hard.

With the valves on auto or activated, no drone in the cablin. Basically its teh same as prior to removal.
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      01-12-2019, 07:48 PM   #13
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My buddy, in Kuwait, did the internal delete on the primary cats. He added some baffles to make the cat chamber act like a free flowing muffler.
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      Yesterday, 11:24 PM   #14
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great thread, might try and have a shop do this. thanks.
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