Hi Flow secondary cats

gunnerxq · 02-08-2021, 10:25 AM

Can anyone recommend some durable hiflow cats for the secondary cats?
If not what size is the exhaust 2.5", 2.75" or 3.0"?

My primary cats have been removed and I know the secondary went bad because it smells really bad and honey comb pieces came out the rear.

neilvan · 02-08-2021, 10:42 AM

N52 cars are basically 2 1/8" at that part (55mm). The factory secondaries are essentiallyy hi-flows as they are only 2 or 250cell cats

gunnerxq · 02-08-2021, 04:21 PM

Quote:

Originally Posted by neilvan

N52 cars are basically 2 1/8" at that part (55mm). The factory secondaries are essentiallyy hi-flows as they are only 2 or 250cell cats

https://www.amazon.com/dp/B01N9JJPLR...15NW6RG5KDF454
What do you think about these 400 cell 2.5" cats? It's hard to find good high flow cats. It shouldn't be a problem for me to modify for the size difference.

Will there be a huge reduction in HP even with the primary cats removed?

neilvan · 02-09-2021, 08:09 AM

The lower number of cells the "higher flow" they are. Ive heard somewhere that stock are 250 so you would be adding more restriction.

If I were you I would go with a Vibrant 2.25" in/out cat, they are 200cell, metal core.

2.5" might be too much of a step up; Would have to make 2 adapters or fill with weld which is less than ideal

gunnerxq · 02-09-2021, 12:22 PM

Thanks! I would have never known these were 200 cell most places don't carry these anymore and don't list how many cells they have.

02-08-2021, 10:25 AM	#1
gunnerxq Lieutenant Colonel 240 Rep 1,838 Posts Drives: 2015 335i xDrive 6MT Join Date: Sep 2010 Location: New York iTrader: (1)	Hi Flow secondary cats Can anyone recommend some durable hiflow cats for the secondary cats? If not what size is the exhaust 2.5", 2.75" or 3.0"? My primary cats have been removed and I know the secondary went bad because it smells really bad and honey comb pieces came out the rear. __________________ Former E90 325i: Koni special active red, eibach pro-kit springs, Remus exhaust, stage 3 intake manifold,Stage 2 AA tune, BMW Short shift kit. Silicon intake pipe. M3 control arms front, M3 rear. ECS trailing arm with whiteline bushings. Purple powerflex subframe bushings. Yellow power flex upper shock mounts. Single mass flywheel OE weight.
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02-08-2021, 10:42 AM	#2
neilvan Major 868 Rep 1,379 Posts Drives: 09 E90 335i M-Sport 6MT RWD Join Date: Nov 2017 Location: Ontario, Canada iTrader: (0) Garage List 2007 BMW E61 530xi [0.00] 1993 Mazda Miata [0.00] 2009 BMW E90 335i [0.00]	N52 cars are basically 2 1/8" at that part (55mm). The factory secondaries are essentiallyy hi-flows as they are only 2 or 250cell cats
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02-09-2021, 08:09 AM	#4
neilvan Major 868 Rep 1,379 Posts Drives: 09 E90 335i M-Sport 6MT RWD Join Date: Nov 2017 Location: Ontario, Canada iTrader: (0) Garage List 2007 BMW E61 530xi [0.00] 1993 Mazda Miata [0.00] 2009 BMW E90 335i [0.00]	The lower number of cells the "higher flow" they are. Ive heard somewhere that stock are 250 so you would be adding more restriction. If I were you I would go with a Vibrant 2.25" in/out cat, they are 200cell, metal core. 2.5" might be too much of a step up; Would have to make 2 adapters or fill with weld which is less than ideal
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02-09-2021, 12:22 PM	#5
gunnerxq Lieutenant Colonel 240 Rep 1,838 Posts Drives: 2015 335i xDrive 6MT Join Date: Sep 2010 Location: New York iTrader: (1)	Thanks! I would have never known these were 200 cell most places don't carry these anymore and don't list how many cells they have. __________________ Former E90 325i: Koni special active red, eibach pro-kit springs, Remus exhaust, stage 3 intake manifold,Stage 2 AA tune, BMW Short shift kit. Silicon intake pipe. M3 control arms front, M3 rear. ECS trailing arm with whiteline bushings. Purple powerflex subframe bushings. Yellow power flex upper shock mounts. Single mass flywheel OE weight.
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