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      09-22-2021, 12:08 PM   #1
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Sports cat on a stock exhaust?

Hi guys,

Just a quick one, my 435i N55 currently has a res delete and itís going in for a sports cat to be fitted. The garage have told me the sound increase will be quite noticeable with this new sports cat fitted. Does anyone know how much increase I should expect sound wise? I do have a stock exhaust and a res delete. I donít want too high expectations haha.

Thanks in advance
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      09-22-2021, 12:22 PM   #2
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I didn't delete my resonators but when i installed my high flow catted downpipe it was significantly louder. I didn't take any db readings or anything but there was absolutely no doubt that it was louder. That being said, without resonators you might find the sound to be a little tinny or ping-y with a high flow cat, just FYI. Some people like that though.
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      09-22-2021, 12:27 PM   #3
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Lucky for you i have videos of all of this but not exactly in the order you did... I installed a fabspeed catted DP on completely stock exhaust (res + axleback), then later deleted the resonator. Most catted DPs don't change the volume significantly when you still have stock axleback, but you will get more turbo noise, a little more volume, rasp, and burble.







I personally like catted DP + res delete with stock axleback as it is tame enough to not drone or be excessively loud but still sounds good.
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      09-22-2021, 01:13 PM   #4
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Quote:
Originally Posted by njdangelo View Post
I didn't delete my resonators but when i installed my high flow catted downpipe it was significantly louder. I didn't take any db readings or anything but there was absolutely no doubt that it was louder. That being said, without resonators you might find the sound to be a little tinny or ping-y with a high flow cat, just FYI. Some people like that though.
Thank you. Did you own a N55 BMW when you did that at the time? Yeah I do care about the volume I just really wanted more sound whilst keeping it legal
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      09-22-2021, 01:33 PM   #5
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Quote:
Originally Posted by F36 435i M View Post
Thank you. Did you own a N55 BMW when you did that at the time? Yeah I do care about the volume I just really wanted more sound whilst keeping it legal
Not sure what you are asking, yes i own it, its my car lol... i still own it.
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      09-22-2021, 01:34 PM   #6
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Originally Posted by thejeremyman9 View Post
Not sure what you are asking, yes i own it, its my car lol... i still own it.
Was quoting the guy above your post ^. Thanks for your message too
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      09-22-2021, 06:35 PM   #7
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Quote:
Originally Posted by F36 435i M View Post
Quote:
Originally Posted by njdangelo View Post
I didn't delete my resonators but when i installed my high flow catted downpipe it was significantly louder. I didn't take any db readings or anything but there was absolutely no doubt that it was louder. That being said, without resonators you might find the sound to be a little tinny or ping-y with a high flow cat, just FYI. Some people like that though.
Thank you. Did you own a N55 BMW when you did that at the time? Yeah I do care about the volume I just really wanted more sound whilst keeping it legal
Nope b58
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      09-22-2021, 07:17 PM   #8
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Quote:
Originally Posted by njdangelo View Post
Nope b58
It may be a slightly different experience for me then as mine is a N55. I guess Iíll just find out and see
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      09-23-2021, 01:01 PM   #9
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Usually the recommendations for nicer sounding exhaust (and louder):
1) Replace your down pipe first.
and then if you want more...
2) Replace the muffler with a cat-back

Usually the DP gives most people what they are looking for, but nothing beats the sound of a better exhaust.
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      09-23-2021, 01:28 PM   #10
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Quote:
Originally Posted by Wires View Post
Usually the recommendations for nicer sounding exhaust (and louder):
1) Replace your down pipe first.
and then if you want more...
2) Replace the muffler with a cat-back

Usually the DP gives most people what they are looking for, but nothing beats the sound of a better exhaust.
It's actually a little more nuanced than this, and the fundamental problem is that most people ask what exact sounds "good" or "best" when that is highly subjective. OP's question was a little point focused on volume (which is a little easier to answer quantitatively), but everyone's tolerance for volume, drone, rasp, etc, is different. Two people with the exact same setup, and one person complains it drones unbearably and other says it sounds awesome no drone (seen this with AWE and borla, especially paired with catless DP).

The other important thing to remember is that DP adds performance and is a prerequisite for tunes whereas exhaust adds nothing for performance and is purely for sound. DP also affects emissions, exhaust does not. Also, a catback replaces the mid pipe and the muffler, whereas an axleback just replaces the muffler. For a N55 F3x, there is a single resonator in the midpipe, which will make a difference if you get a catback vs a axleback as some catbacks are non resonated.

Another way to think about it is the effect each component post-turbo affects the exhaust volume. Of course, there is more than volume, there is drone, rasp, tone, etc. But volume is the easiest to quantify. So, think of it this way:

Stock muffler reduces volume 50%
Stock resonator reduces volume 20%
Stock DP reduces volume 20%. Catted DP reduces 10% and catless 0%.

So if 10/10 volume is catless DP and straight pipe (res and muffler delete), the OEM volume is 1/10 (and it is indeed very quiet). If you go catless with stock res/muffler, you are at 3/10, catted DP only 2/10. Res delete and catted DP you are at 4/10. This trend holds true with my own personal experience and all the videos and discussion i have seen with exhausts. Going from OEM DP to catted DP on my own car with completely stock exhaust only raised the volume a few dB. You almost couldnt tell unless you listen carefully. Of course, with res delete, it makes a bigger difference, since you have already removed another "muffler" from the system.

Finally, its important to remember that the muffler has the Helmholtz chamber which is critical to reduce drone. So a muffler delete will have the single largest impact on drone.

Last edited by thejeremyman9; 09-23-2021 at 01:38 PM..
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      09-23-2021, 01:41 PM   #11
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Quote:
Originally Posted by thejeremyman9 View Post
It's actually a little more nuanced than this, and the fundamental problem is that most people ask what exact sounds "good" or "best" when that is highly subjective. OP's question was a little point focused on volume (which is a little easier to answer quantitatively), but everyone's tolerance for volume, drone, rasp, etc, is different. Two people with the exact same setup, and one person complains it drones unbearably and other says it sounds awesome no drone (seen this with AWE and borla, especially paired with catless DP).

The other important thing to remember is that DP adds performance and is a prerequisite for tunes whereas exhaust adds nothing for performance and is purely for sound. DP also affects emissions, exhaust does not. Also, a catback replaces the mid pipe and the muffler, whereas an axleback just replaces the muffler. For a N55 F3x, there is a single resonator in the midpipe, which will make a difference if you get a catback vs a axleback as some catbacks are non resonated.

Another way to think about it is the effect each component post-turbo affects the exhaust volume. Of course, there is more than volume, there is drone, rasp, tone, etc. But volume is the easiest to quantify. So, think of it this way:

Stock muffler reduces volume 50%
Stock resonator reduces volume 20%
Stock DP reduces volume 20%. Catted DP reduces 10% and catless 0%.

So if 10/10 volume is catless DP and straight pipe (res and muffler delete), the OEM volume is 1/10 (and it is indeed very quiet). If you go catless with stock res/muffler, you are at 3/10, catted DP only 2/10. Res delete and catted DP you are at 4/10. This trend holds true with my own personal experience and all the videos and discussion i have seen with exhausts. Going from OEM DP to catted DP on my own car with completely stock exhaust only raised the volume a few dB. You almost couldnt tell unless you listen carefully. Of course, with res delete, it makes a bigger difference, since you have already removed another "muffler" from the system.

Finally, its important to remember that the muffler has the Helmholtz chamber which is critical to reduce drone. So a muffler delete will have the single largest impact on drone.
Dang you know your stuff. Yeah I didnít want to delete the muffler as I spoke to someone on Facebook who had both a res delete and muffler delete and he did admit for a daily it wasnít ideal as the drone is quite bad especially on a motorway. I may get a modified back box at some point in the future but the sports cat was sold to me mainly due to me being able to keep the exhaust valve whilst getting some better sound and performance at the same time. I guess Iíll just find out tomorrow how good the sound is. I didnít think the res delete made too much of a difference.
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      09-23-2021, 01:58 PM   #12
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Quote:
Originally Posted by F36 435i M View Post
Dang you know your stuff. Yeah I didnít want to delete the muffler as I spoke to someone on Facebook who had both a res delete and muffler delete and he did admit for a daily it wasnít ideal as the drone is quite bad especially on a motorway. I may get a modified back box at some point in the future but the sports cat was sold to me mainly due to me being able to keep the exhaust valve whilst getting some better sound and performance at the same time. I guess Iíll just find out tomorrow how good the sound is. I didnít think the res delete made too much of a difference.
My example above assumes everything is linear/applied in "parallel" when in reality its a little more applied in "series" than that. Meaning once you remove one component the effect of removing another component is further increased. So in other words the change going from OEM DP to catted DP will be more significant if you have already deleted the resonator.

I think you will be pleased with the sound, the only question is if it will be "loud enough" for your taste.
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      09-23-2021, 02:14 PM   #13
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Quote:
Originally Posted by thejeremyman9 View Post
My example above assumes everything is linear/applied in "parallel" when in reality its a little more applied in "series" than that. Meaning once you remove one component the effect of removing another component is further increased. So in other words the change going from OEM DP to catted DP will be more significant if you have already deleted the resonator.

I think you will be pleased with the sound, the only question is if it will be "loud enough" for your taste.
Yes thanks for the info. Itís a hard one because a muffler delete is just not an option for me due to the drone. So the last thing to do will be a modified muffler but Iíll look at that once Iíve heard the catted downpipe
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      09-23-2021, 02:58 PM   #14
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Quote:
Originally Posted by F36 435i M View Post
Yes thanks for the info. Itís a hard one because a muffler delete is just not an option for me due to the drone. So the last thing to do will be a modified muffler but Iíll look at that once Iíve heard the catted downpipe
Keep this handy for muffler modification: https://f30.bimmerpost.com/forums/sh...d.php?t=819125
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      09-23-2021, 03:35 PM   #15
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Originally Posted by thejeremyman9 View Post
Keep this handy for muffler modification: https://f30.bimmerpost.com/forums/sh...d.php?t=819125
Thank you but Iíve seen this post before, Iím not really the a mechanic type of person and donít really want to DIY it and I did ask my local shops if they would do this to my muffler and sadly they wonít
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      09-24-2021, 12:15 PM   #16
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Update! Got it back today and boy it does sound a lot better than before! A sports cat and res delete combination I would recommend to any N55 owner. I think a muffler delete with this would be too much though as there is no drone currently
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      09-24-2021, 02:46 PM   #17
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Quote:
Originally Posted by F36 435i M View Post
Update! Got it back today and boy it does sound a lot better than before! A sports cat and res delete combination I would recommend to any N55 owner. I think a muffler delete with this would be too much though as there is no drone currently
Same as my experience
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