Gutted cats?

[te37]

Moring,
I have been doing a little research to see if this is something worth doing. Was wondering if someone has ever done it on these cars. The only issues I see is the fact that removing the catalytic material from the inside and creating a big void in the pipe potentially creating a stagnant high-pressure zone.
Thanks,
Nick

[schnell325]

For the price of some of the catless DPs available, I wouldn't bother. I'm keeping my stock DPs to either put back on the car if I ever sell her or give to the new owner.

[ciaranob]

Ha - when I clicked on this thread I was expecting to see some gruesome images, thinking .. really!? Note to self, first engage brain, then click !

[MNoob]

How could you. you people are sick.

[PayamFSU]

Originally Posted by MNoob

How could you. you people are sick.

Lol beat me to it

[SanchoDivine]

Originally Posted by te37

Moring,
I have been doing a little research to see if this is something worth doing. Was wondering if someone has ever done it on these cars. The only issues I see is the fact that removing the catalytic material from the inside and creating a big void in the pipe potentially creating a stagnant high-pressure zone.
Thanks,
Nick

There are 4 catalytic converters. Which ones are you looking to do?

If you are thinking of gutting the primaries, it would probably make more sense to just buy some aftermarket downpipes. Keep in mind that you will get a check engine light if you mess with these cats and will need some sort of tune or aftermarket part to remove it (and to really take advantage of having catless downpipes).

Some folks have hallowed out or cut out the secondary cats and welded in pipes or replaced that portion of the mid-pipe completely. Those that have hallowed out the cats or cut them out posted pictures but haven't posted any videos or sound clips (have requested them to do so with no luck). You won't get a check engine light with any of these routes.

I replaced my mid-pipe with the FabSpeed option and it sounds pretty good. The mid-pipe replacement is expensive but catalytic converters are expensive also. I believe you can get in trouble if you try to sell the car without the cats so I would recommend not destroying them so that you can restore the emission back to normal when you want to sell the car. If you hallow the cats or cut them out, please share a video or something so that we can get an idea on how it sounds!

[te37]

Originally Posted by SanchoDivine

There are 4 catalytic converters. Which ones are you looking to do?

If you are thinking of gutting the primaries, it would probably make more sense to just buy some aftermarket downpipes. Keep in mind that you will get a check engine light if you mess with these cats and will need some sort of tune or aftermarket part to remove it (and to really take advantage of having catless downpipes).

Some folks have hallowed out or cut out the secondary cats and welded in pipes or replaced that portion of the mid-pipe completely. Those that have hallowed out the cats or cut them out posted pictures but haven't posted any videos or sound clips (have requested them to do so with no luck). You won't get a check engine light with any of these routes.

I replaced my mid-pipe with the FabSpeed option and it sounds pretty good. The mid-pipe replacement is expensive but catalytic converters are expensive also. I believe you can get in trouble if you try to sell the car without the cats so I would recommend not destroying them so that you can restore the emission back to normal when you want to sell the car. If you hallow the cats or cut them out, please share a video or something so that we can get an idea on how it sounds!

I would be doing it to the primary cats and with a second set not my originals. So I would have the originals to put back on the car if need be. The main purpose behind this is to free up some noise muffled by the cats, also a little "less" suspicious when I take the car in for its maintnence. I also like the OEM quality of the factory cats and the flex sections.

Thanks

[SanchoDivine]

Originally Posted by te37

I would be doing it to the primary cats and with a second set not my originals. So I would have the originals to put back on the car if need be. The main purpose behind this is to free up some noise muffled by the cats, also a little "less" suspicious when I take the car in for its maintnence. I also like the OEM quality of the factory cats and the flex sections.

Thanks

Well the downpipes are pretty hidden and you'll have a check engine light along with the associated codes being thrown by the gutted cats but at least you know the fit will be perfect.

[robbo mcs]

I've not done it on F82. However, I have seen it done on other turbo BMW's. People have done it for competitions where the cat is supposed to be in place, so it doesn't look obvious to scrutineers etc. Works in other cars no problems. As others said, if you are worried about the void space, just put a pipe down the middle.

[knightarmor]

I'm in the process.of getting the secondary cats replaced. Will post pics as soon as I get my setup back from.my fab guy. Last time I did a secondary cat delete on a turbo four it netted 10hp gain and 20ft lbs of torque.

[mike@x-ph.com]

Not worth it.

You are required by law to put the stock ones back when you sell the car. So you might save a few bucks now but you will need to buy the stock pipes later and they cost a lot more than the aftermarket catless pipes.

[CaryTheLabelGuy]

Originally Posted by mike@x-ph.com

Not worth it.

You are required by law to put the stock ones back when you sell the car. So you might save a few bucks now but you will need to buy the stock pipes later and they cost a lot more than the aftermarket catless pipes.

Exactly. If the OP has a set of spare stock downpipes laying around, cool - have at it. Other than that, it ain't worth it.

[te37]

Thanks for the replies guys but this wasn't a cost or legal question it was more of a question of how the OEM cats gutted would physically work. Did not know if anyone had done it, I know some M5s it has been done.

Thanks,
Nick

[knightarmor]

Quick shot of the secondary catalysts deleted. Installing in the morning. Will try to get some audio.

[knightarmor]

Fitted up this morning. I still have a quiet cabin which is what I want and the exhaust note is a bit deeper. The best part is you can really hear the exhaust (at the rear of the car where it should be) when you're really on the accelerator. I can even hear it over the radio when I've got it set to a medium volume, however it doesn't shake or vibrate the car nor does it overpower the sound of the radio. No drone inside the vehicle either at any RPM.

Throttle response feels better in Efficient mode as well.

Need to charge up my Gopro to get some good audio at the tail pipes.
Some pics-

[humbertin0]

Awesome! Thanks for the update and feedback. Do you have any before and after videos and/or sound clips?

[knightarmor]

Didn't take any before audio. Will try to get some audio of my neighbors stock F80. Will try to get audio of mine today if not maybe tomorrow on my way to work!

[Pak317]

Originally Posted by knightarmor

Didn't take any before audio. Will try to get some audio of my neighbors stock F80. Will try to get audio of mine today if not maybe tomorrow on my way to work!

So you have DP and 2nd cats removed? Can you pm which shop removed your 2nd cats?

[knightarmor]

I have the OEM downpipes with catalytic converters. I only deleted the secondary catalysts.

[knightarmor]

So apparently I had a Legacy YouTube account...

Video's uploaded. Be forewarned they are very boring, so no complaining about how you wasted a few minutes of your life!!

Enjoy!

Efficient-

Sport-

Sport Plus-

[danniexi]

Originally Posted by te37

Thanks for the replies guys but this wasn't a cost or legal question it was more of a question of how the OEM cats gutted would physically work. Did not know if anyone had done it, I know some M5s it has been done.

Thanks,
Nick

i get what you're saying and have thought about it as well. OEM downpipes can be had for cheap and gutting them should be pretty straight forward. fitment won't obviously be an issue and won't raise any eyebrows at the dealers (visually at least. i know they can still tell if you're tuned or not).

but my concern (and i think yours as well) would be the flow compared to an aftermarket piece. its not a straight through design so would the exhaust flow be compromised due to its irregular shape? will that turbulence cause any issues in terms of back pressure and would the lack the metal substrate even be worth it as of that point?

[robbo mcs]

Originally Posted by danniexi

i get what you're saying and have thought about it as well. OEM downpipes can be had for cheap and gutting them should be pretty straight forward. fitment won't obviously be an issue and won't raise any eyebrows at the dealers (visually at least. i know they can still tell if you're tuned or not).

but my concern (and i think yours as well) would be the flow compared to an aftermarket piece. its not a straight through design so would the exhaust flow be compromised due to its irregular shape? will that turbulence cause any issues in terms of back pressure and would the lack the metal substrate even be worth it as of that point?

If you want to go stealth then you get a stock downpipe, and just put a pipe through the middle. That is what I have done with other BMW racecars (not F82). That way it looks stock externally, but is running a straight pipe through the middle of where the cat used to be.