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BMW M5 F90 (2018+) General Forums Engine, Exhaust, Drivetrain, Tuning Modifications    F90 secondary downpipes gains

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      03-19-2020, 12:28 PM   #1
AMOR
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Question F90 secondary downpipes gains

According to the fabspeed dyno graphs, the secondary cat bypass adds 50 hp to the wheels on F90 and does not require a tune, since secondaries do not have O2 sensors in them. How true is that? Seems like a crazy gain from just a secondaries delete... I had an impression that such power increase is only possible with primary cat delete??

https://www.fabspeed.com/bmw-m5-f90-...-bypass-pipes/
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      03-19-2020, 01:02 PM   #2
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puffery
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      03-19-2020, 04:18 PM   #3
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Quote:
Originally Posted by Higgs Boson View Post
puffery
At first, thought so too. But it’s a pretty reputable manufacturer, supplying parts for exotic cars and Porsches. Don’t think they would fake the dyno results. Another thing I noticed is that factory cats in primary downpipes vs race cats are just 10 hp difference according to their dyno.
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      03-19-2020, 04:35 PM   #4
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Quote:
Originally Posted by AMOR View Post
At first, thought so too. But it’s a pretty reputable manufacturer, supplying parts for exotic cars and Porsches. Don’t think they would fake the dyno results. Another thing I noticed is that factory cats in primary downpipes vs race cats are just 10 hp difference according to their dyno.
I used to think they were reputable too since they market themselves well.
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      05-03-2021, 11:43 PM   #5
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I think it's bs! 50 hp no way. Maybe 7hp. The f90 secondary cats flow is not as restricted as some. I was reading a different thread with a flow bench test. Quoted from post:
F90 Factory second cat flows 542cfm at 28 H20
For reference an open 2.5" pipe flows 515cfm
An open 3" pipe maxes my bench at 702cfm
2017 Z06 secondary @ 482cfm
He said the Z06 gained 35 horse, 18 at the wheels by deleting ALL 4 cats! He said in comparison the F90 on a 3" secondary 21hp at the crank. We are just talking secondary, not all 4 cats. 50 hp lol! Maybe 4whp. The F90 secondary cats are tiny compared to the Z06's.
https://f90.bimmerpost.com/forums/sh....php?t=1551285

Last edited by ruderegime; 05-03-2021 at 11:55 PM..
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      05-04-2021, 02:37 PM   #6
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2 cars running exact same tune. 1 has full downpipes removed, other has only upper dp removed.

Difference 100-200 dragy is 0.15-0.2. Measured 10x times.

So answer is definitive NO, it does not add 50hp.
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      05-04-2021, 06:22 PM   #7
schnell1982
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lmao at 50whp gain
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      05-04-2021, 07:35 PM   #8
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Quote:
Originally Posted by schnell1982 View Post
lmao at 50whp gain
if you click on the link for secondary pipes they are now claiming more hp then 50, and something like 64 lb of torque. lol
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      05-04-2021, 11:22 PM   #9
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i bought both the primary and secondaries and the car does pull harder. no tune
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      05-05-2021, 12:46 AM   #10
ruderegime
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Quote:
Originally Posted by boost4breakfast View Post
i bought both the primary and secondaries and the car does pull harder. no tune
The primary cats are obviously bigger more restricted. All four would make a difference. Not much gain from the 2 little secondary delet except sound.
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      05-05-2021, 08:25 AM   #11
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hilarious.
Idk whats better, calming 50whp gain or paying $1600 for two metal pipes
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      05-05-2021, 03:01 PM   #12
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Quote:
Originally Posted by ruderegime View Post
The primary cats are obviously bigger more restricted. All four would make a difference. Not much gain from the 2 little secondary delet except sound.
they use high flow HJS cats. their fitment was slightly off on the secondaries but had to grind them a little. still smell a little fumes but you need primaries for the gain for sure. you’re correct with secondaries just being sound. went with them cause they guarantee no CEL. no shakes or vibrations after the install and the car is much faster especially around 3k rpm




Last edited by boost4breakfast; 05-05-2021 at 03:08 PM..
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      05-06-2021, 09:24 PM   #13
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Quote:
Originally Posted by boost4breakfast View Post
Quote:
Originally Posted by ruderegime View Post
The primary cats are obviously bigger more restricted. All four would make a difference. Not much gain from the 2 little secondary delet except sound.
they use high flow HJS cats. their fitment was slightly off on the secondaries but had to grind them a little. still smell a little fumes but you need primaries for the gain for sure. you’re correct with secondaries just being sound. went with them cause they guarantee no CEL. no shakes or vibrations after the install and the car is much faster especially around 3k rpm



I'm glad that your happy with the delete. I have one cat in my Mazdaspeed Miata, and my other 2 modded cars have no cats, and I just sold my C7 Z06 with all 4 cats deleted. If I decide to purchase a F90 M5 I doubt I'll delete the cats doing to my wife wanted me to get a family car. I'll be so happy if I get one.
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