BMW Garage BMW Meets Register Search Today's Posts Mark Forums Read
BMW M5 F90 (2018+) General Forums Engine, Exhaust, Drivetrain, Tuning Modifications    Downpipes Opinion Request

Post Reply
 
Thread Tools Search this Thread
      09-04-2021, 03:19 PM   #1
bcparker2
Private First Class
102
Rep
142
Posts

Drives: BMW M5 (F90)
Join Date: Oct 2020
Location: Texas

iTrader: (0)

Downpipes Opinion Request

We all know that removing all of the cats helps the engine breathe better than catted, but if you could only do one, Primary or Secondary, which would it be and why.
Appreciate 0
      09-04-2021, 05:11 PM   #2
AngryInch
Lieutenant
212
Rep
548
Posts

Drives: 2021 BMW M5 Comp
Join Date: Jul 2021
Location: Canada

iTrader: (0)

Primary... They are stuck literally right behind the turbo... Less heat in the engine back and on the turbo.
Appreciate 0
      09-05-2021, 11:08 AM   #3
M5KEITH
Second Lieutenant
M5KEITH's Avatar
129
Rep
214
Posts

Drives: M5
Join Date: Jan 2021
Location: Massachusetts

iTrader: (0)

Secondary cats because they don’t impact emissions. All emissions readings are from the primaries. If you don’t live in a emission strict state remove both but your car will smell fuel/eggs removing both.
Appreciate 0
      09-17-2021, 12:17 PM   #4
GTATX
Lieutenant Colonel
GTATX's Avatar
United_States
1104
Rep
1,607
Posts

Drives: 2020 M8 Comp First Edition
Join Date: Nov 2012
Location: Georgetown TX

iTrader: (0)

Garage List
If you are planning on tuning I would swap the primary and keep secondary. Removing primary will cause cel but tuner can bypass it.
__________________
GT
2020 BMW M8 Comp First Edition
2019 Panamera Turbo
2021 BMW X6M Comp
2019 BMW M5
2018 Maserati Ghibli SQ4 GranSport
Appreciate 0
      09-17-2021, 05:15 PM   #5
Blackedm5f90
Starlink
No_Country
24
Rep
92
Posts

Drives: 2022 BMW M5 Competition
Join Date: Sep 2021
Location: East coast, USA

iTrader: (0)

I live in VA where emissions are tested every 2 years. In this scenario going catted for primaries I believe is my best option?
Appreciate 0
      09-17-2021, 07:06 PM   #6
bcparker2
Private First Class
102
Rep
142
Posts

Drives: BMW M5 (F90)
Join Date: Oct 2020
Location: Texas

iTrader: (0)

Thanks GTATX you're catless all the way correct? I have an old 68 Chevy truck obviously no cats, it smells like fuel and etc like as you would expect from an old car. is there something about new technology that makes it smell worse than old cars, or will it smell the same more or less? from all of the complaints about it it has me confused about how bad it could be.
Appreciate 0
      09-17-2021, 07:25 PM   #7
pbonsalb
Lieutenant General
5179
Rep
10,556
Posts

Drives: 18 F90 M5, 99 E36 M3 Turbo
Join Date: Feb 2011
Location: New England

iTrader: (4)

I think a lot of people complaining are not tuned for catless. I once went catless before I had a tune and the smell was terrible. With a tune, I almost never noticed it. On cold start and in heavy traffic with hot weather and no breeze it would still be noticeable but not bothersome to me. People have different tolerances.

For my F90 M5, I am inclined to go high flow primary cats and catless secondaries and leave a little power on the table. It is a comfy cruiser, winter beater, construction material and tool hauler to me, not an all out sports car though it does have very good performance for its size. Best in class, probably, which is why I bought an F90 instead of a Panamerica Turbo or RS7 or CTS-V or E63 AMG. The only other car that tempted me was a 991.2 Turbo, but it cost 50% more and was not nearly as useful. I will buy one later to complement the F90 and it may well end up catless.
Appreciate 0
      09-17-2021, 07:34 PM   #8
AngryInch
Lieutenant
212
Rep
548
Posts

Drives: 2021 BMW M5 Comp
Join Date: Jul 2021
Location: Canada

iTrader: (0)

I don’t smell anything but it could be the covid haha
Appreciate 2
JK-M561.00
Damzz50.50
      09-17-2021, 08:48 PM   #9
pbonsalb
Lieutenant General
5179
Rep
10,556
Posts

Drives: 18 F90 M5, 99 E36 M3 Turbo
Join Date: Feb 2011
Location: New England

iTrader: (4)

There you go. Finally something positive about Covid! More performance.
Appreciate 0
      09-17-2021, 09:19 PM   #10
GTATX
Lieutenant Colonel
GTATX's Avatar
United_States
1104
Rep
1,607
Posts

Drives: 2020 M8 Comp First Edition
Join Date: Nov 2012
Location: Georgetown TX

iTrader: (0)

Garage List
Quote:
Originally Posted by bcparker2 View Post
Thanks GTATX you're catless all the way correct? I have an old 68 Chevy truck obviously no cats, it smells like fuel and etc like as you would expect from an old car. is there something about new technology that makes it smell worse than old cars, or will it smell the same more or less? from all of the complaints about it it has me confused about how bad it could be.
I am completely cat-less correct. U only smell it when stationary or as usual ur wife will complain regardless but I personally don't have a problem with it. Now if for 100% sure I can keep my same performance and keep the secondary cat or go high flow primary cats I would definitely do it.

Also smell is with windows down only.

Cat-less also makes the car more raspier so if u like deeper rumble high flow cars might be another option. I was really looking into changes my exhaust set up from Remus catback to Akra but was told Remus is the deepest sounding exhaust for f90.
__________________
GT
2020 BMW M8 Comp First Edition
2019 Panamera Turbo
2021 BMW X6M Comp
2019 BMW M5
2018 Maserati Ghibli SQ4 GranSport
Appreciate 2
      09-18-2021, 06:52 AM   #11
DrivenAgain
MFJWADE
119
Rep
351
Posts

Drives: 2018 BMW M5
Join Date: Dec 2020
Location: MD

iTrader: (0)

I'm going catless secondaries. I don't have a flash tune to code out the CEL, and I dont want any smell. Sound is not a concern for me, bump in performance and no smell/CEL are my top priorities. I'm trying to improve my 60-130 and I've reached the cars current potential at 6.71 with stock downpipes and current state of mods.
__________________
2018 M5 Singapore Grey CCBs/Utku Noa E45 ECU/xHP TCU/PG-Intake/PG-Lower Downpipes
Appreciate 0
      09-18-2021, 09:01 AM   #12
Blackedm5f90
Starlink
No_Country
24
Rep
92
Posts

Drives: 2022 BMW M5 Competition
Join Date: Sep 2021
Location: East coast, USA

iTrader: (0)

To piggy back on this thread, I have heard folks say that emissions only looks at primary cats and not secondary. My question is how? Emission tests the air coming out the exhaust pipe so really the cat it goes through shouldn't make a difference, would it?

In VA, we also have these automated emission testing boxes that are put on exit/on-ramp for major highways so it quite literally is just your exhaust and nothing else.
Appreciate 0
      09-18-2021, 09:22 AM   #13
GTATX
Lieutenant Colonel
GTATX's Avatar
United_States
1104
Rep
1,607
Posts

Drives: 2020 M8 Comp First Edition
Join Date: Nov 2012
Location: Georgetown TX

iTrader: (0)

Garage List
Quote:
Originally Posted by Blackedm5f90 View Post
To piggy back on this thread, I have heard folks say that emissions only looks at primary cats and not secondary. My question is how? Emission tests the air coming out the exhaust pipe so really the cat it goes through shouldn't make a difference, would it?

In VA, we also have these automated emission testing boxes that are put on exit/on-ramp for major highways so it quite literally is just your exhaust and nothing else.
Primary cats have O2 sensors which gather the emissions data. Sensor is right after the filtration material so that's why when u go cat-less the readings are off and u have an engine light.
__________________
GT
2020 BMW M8 Comp First Edition
2019 Panamera Turbo
2021 BMW X6M Comp
2019 BMW M5
2018 Maserati Ghibli SQ4 GranSport
Appreciate 0
      09-18-2021, 09:47 AM   #14
Blackedm5f90
Starlink
No_Country
24
Rep
92
Posts

Drives: 2022 BMW M5 Competition
Join Date: Sep 2021
Location: East coast, USA

iTrader: (0)

Quote:
Originally Posted by GTATX View Post
Primary cats have O2 sensors which gather the emissions data. Sensor is right after the filtration material so that's why when u go cat-less the readings are off and u have an engine light.
Thanks and for in person testing, that would be an issue but in case of roadside emissions tests would it make a difference which cat the air went through before coming out the exhaust?
Appreciate 0
      09-18-2021, 09:53 AM   #15
pbonsalb
Lieutenant General
5179
Rep
10,556
Posts

Drives: 18 F90 M5, 99 E36 M3 Turbo
Join Date: Feb 2011
Location: New England

iTrader: (4)

OBD2 monitoring is right after the primary cats and not influenced by the secondary cats. I don’t know the standard for sniffer tests — could be the smog station has the readings the factory would expect after the secondary cats. Or maybe it is a general standard and the additional cleanup from the secondary cats is not really needed.

Roadside van sniffer won’t be as accurate as a probe in the tailpipe so I would not worry about that if removing just one set of cats. It is more of a gross polluter thing. It won’t have accuracy or standards to distinguish your 2021 car emissions from 1995 car emissions.
Appreciate 0
      09-18-2021, 11:07 AM   #16
mike@x-ph.com
Joint Chiefs of Staff
mike@x-ph.com's Avatar
United_States
23798
Rep
190,172
Posts

Drives: 07-335/12-328/18-M4/21-M4CP
Join Date: Sep 2013
Location: Las Vegas

iTrader: (23)

Primary will improve the sound and power more than secondary but are also not legal in some states.

If legal, upgrade the primaries. If not, it's not worth the hassle either get catted primary or catless secondary
__________________
Check out our current sale by clicking on this link!
https://x-ph.com/sale/

Phone number 702-494-9435
Appreciate 0
      10-12-2021, 11:33 AM   #17
M5-Dubai
Enlisted Member
0
Rep
32
Posts

Drives: F90 M5 Comp (2019)
Join Date: Oct 2021
Location: Dubai

iTrader: (0)

Quote:
Originally Posted by mike@x-ph.com View Post
Primary will improve the sound and power more than secondary but are also not legal in some states.

If legal, upgrade the primaries. If not, it's not worth the hassle either get catted primary or catless secondary
I have a question what is legal in CT, can I use downpipes or catted downpipes or is that illegal?
Appreciate 0
      10-12-2021, 12:45 PM   #18
Blackedm5f90
Starlink
No_Country
24
Rep
92
Posts

Drives: 2022 BMW M5 Competition
Join Date: Sep 2021
Location: East coast, USA

iTrader: (0)

Quote:
Originally Posted by M5-Dubai View Post
I have a question what is legal in CT, can I use downpipes or catted downpipes or is that illegal?
Hey... wait a minute... I thought your location was Dubai... lol
Appreciate 1
FatRear081425.50
      10-12-2021, 01:43 PM   #19
FatRear08
Major
FatRear08's Avatar
1426
Rep
1,195
Posts

Drives: F90 M5
Join Date: Apr 2012
Location: HHI

iTrader: (0)

Quote:
Originally Posted by Blackedm5f90 View Post
Hey... wait a minute... I thought your location was Dubai... lol
Yeah me too…hahaha
Appreciate 0
      10-12-2021, 03:22 PM   #20
eric97hoh
First Lieutenant
United_States
87
Rep
315
Posts

Drives: 2020 bmw m5
Join Date: Aug 2021
Location: california

iTrader: (0)

Quote:
Originally Posted by pbonsalb View Post
I think a lot of people complaining are not tuned for catless. I once went catless before I had a tune and the smell was terrible. With a tune, I almost never noticed it. On cold start and in heavy traffic with hot weather and no breeze it would still be noticeable but not bothersome to me. People have different tolerances.

For my F90 M5, I am inclined to go high flow primary cats and catless secondaries and leave a little power on the table. It is a comfy cruiser, winter beater, construction material and tool hauler to me, not an all out sports car though it does have very good performance for its size. Best in class, probably, which is why I bought an F90 instead of a Panamerica Turbo or RS7 or CTS-V or E63 AMG. The only other car that tempted me was a 991.2 Turbo, but it cost 50% more and was not nearly as useful. I will buy one later to complement the F90 and it may well end up catless.
do you think primary catless and not touching secondaries is better ? or primary catted and secondary catless is better as far as sound smell power go ?
__________________
2020 BMW m5 with some bmc filters, charcoal filter delete, and Dinan turbo inlets.

Previous BMW model 2018 bmw 340i FBO custom e50 tune 500 wheel
Appreciate 0
      10-12-2021, 05:56 PM   #21
pbonsalb
Lieutenant General
5179
Rep
10,556
Posts

Drives: 18 F90 M5, 99 E36 M3 Turbo
Join Date: Feb 2011
Location: New England

iTrader: (4)

Really good question. Probably getting rid of the bigger primary cat makes more power. Probably getting rid of the smaller secondary would be best for smell. If money was no object, I would buy HKS 200 cell primaries and run catless secondaries. If all out performance was the goal, I would run catless primaries and secondaries.
Appreciate 0
      10-12-2021, 06:12 PM   #22
eric97hoh
First Lieutenant
United_States
87
Rep
315
Posts

Drives: 2020 bmw m5
Join Date: Aug 2021
Location: california

iTrader: (0)

Quote:
Originally Posted by pbonsalb View Post
Really good question. Probably getting rid of the bigger primary cat makes more power. Probably getting rid of the smaller secondary would be best for smell. If money was no object, I would buy HKS 200 cell primaries and run catless secondaries. If all out performance was the goal, I would run catless primaries and secondaries.
I might even run primary downpipes catless and secondary catted or stock so I get the power gains but its not obnoxiously loud or smelly because I'm pairing it with dinan x pipe
__________________
2020 BMW m5 with some bmc filters, charcoal filter delete, and Dinan turbo inlets.

Previous BMW model 2018 bmw 340i FBO custom e50 tune 500 wheel
Appreciate 0
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -5. The time now is 10:50 AM.




m5post
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST