High-flow primary cat

Intotheblue · 06-28-2015, 11:18 AM

I just had my secondary cats replaced with straight pipe and am entertaining the idea of getting a high flow cat for the primary. Has anyone done this yet and noticed any gains?

Can anyone help me out with which Magnaflow cat part number is a direct or universal fit? I feel in way over my head when browsing their selection.

Eagle1oh7 · 06-28-2015, 11:59 AM

There are quite a few threads on this already.

Intotheblue · 06-28-2015, 12:39 PM

I'm sure, but I didn't have much luck with a search, every thread seems to wander towards header talk.

Eagle1oh7 · 06-28-2015, 01:54 PM

The headers are catted if you're talking about primaries.

Ali-E90 · 06-28-2015, 02:29 PM

I think OP is looking for high flow cat options that don't require changing the headers. Is this possible, or are aftermarket headers the only way to change the primary cats?

Intotheblue · 06-28-2015, 02:52 PM

Yes exactly, headers are out of my budget. I didn't think to look how the primary cat was mounted when the car was on the lift at the exhaust shop, or if there are 1 or 2 primary cats. I'm thinking its not worth the trouble but curious anyways.

Eagle1oh7 · 06-28-2015, 09:14 PM

Quote:

Originally Posted by Ali-323i

I think OP is looking for high flow cat options that don't require changing the headers. Is this possible, or are aftermarket headers the only way to change the primary cats?

There no primary cat options except gutting them or doing a full on header swap.

TheSt|G · 06-29-2015, 09:07 AM

The primary cat is part of the header setup coming off the engine. Magnaflow cats are discount garbage for cheap cars, avoid them.

mike-y · 06-29-2015, 03:28 PM

To do what the OP is asking, you'd have to remove your factory headers, cut out the factory cats, and weld in some sort of aftermarket cat. it's quite a bit more work than just swapping the headers.

mmmnot · 06-30-2015, 08:24 AM

Quote:

Originally Posted by mike-y

To do what the OP is asking, you'd have to remove your factory headers, cut out the factory cats, and weld in some sort of aftermarket cat. it's quite a bit more work than just swapping the headers.

Theoretically - would you need to do this as well just to gut the cats?

I've seen threads where people will actually gut the primary stock cats for better flow. Not sure what the dyno results say - however, it is an option.

Mike. · 06-30-2015, 09:16 AM

Quote:

Originally Posted by mmmnot

Quote:

Originally Posted by mike-y

To do what the OP is asking, you'd have to remove your factory headers, cut out the factory cats, and weld in some sort of aftermarket cat. it's quite a bit more work than just swapping the headers.

Theoretically - would you need to do this as well just to gut the cats?

I've seen threads where people will actually gut the primary stock cats for better flow. Not sure what the dyno results say - however, it is an option.

Yes you would have to remove them to gut them

Intotheblue · 06-30-2015, 10:51 AM

Well count me out, definitely doesn't seem cheap enough to even consider. Thanks for the info.

Rival · 07-01-2015, 11:07 AM

hi flow cats have never done too well in my exp.

when i was still with american V8's and now bmw's, avoid hi flow aftermarket cats.

Rival · 07-01-2015, 11:14 AM

hi flow cats have never done too well in my exp.

when i was still with american V8's and now bmw's, avoid hi flow aftermarket cats.

Eagle1oh7 · 07-01-2015, 12:18 PM

Quote:

Originally Posted by Rival

hi flow cats have never done too well in my exp.

when i was still with american V8's and now bmw's, avoid hi flow aftermarket cats.

Why's that?

TheSt|G · 07-02-2015, 09:35 AM

Quote:

Originally Posted by Eagle1oh7

Why's that?

Because no one is willing to actually spend the money needed to get something worthwhile like HJS.

Here is a hi flow Magnaflow CAT I pulled off a friend's Miata last week. Tell me if you can spot the issue:

mmmnot · 07-02-2015, 09:54 AM

Is there a point of even calling that a 'cat' anymore? Just looks like a bloated pipe with a hole in the middle?

Rival · 07-02-2015, 10:41 AM

Quote:

Originally Posted by TheSt|G

Because no one is willing to actually spend the money needed to get something worthwhile like HJS.

Here is a hi flow Magnaflow CAT I pulled off a friend's Miata last week. Tell me if you can spot the issue:

it looks like a bullet muffler.

hassmaschine · 07-02-2015, 11:30 AM

gutting a cat isn't a good idea either. the exhaust will lose all its velocity due to the huge expansion in volume. I'd wager a gutted cat actually loses performance vs just leaving it alone, especially with them placed so close to the primaries on the stock manifolds.

IMO - either do headers or don't bother messing with it at all.

TheSt|G · 07-02-2015, 11:55 AM

Quote:

Originally Posted by mmmnot

Is there a point of even calling that a 'cat' anymore? Just looks like a bloated pipe with a hole in the middle?

That's the point. The hunk of crap disintegrated.

mmmnot · 07-02-2015, 12:06 PM

I just noticed the lift in a residential garage. Peanut butter and jelly.

TheSt|G · 07-02-2015, 01:40 PM

Quote:

Originally Posted by mmmnot

I just noticed the lift in a residential garage. Peanut butter and jelly.

Yup, makes all my work easy/safer:

06-28-2015, 11:18 AM	#1
Intotheblue Private First Class 19 Rep 149 Posts Drives: 2014 650i Coupe Join Date: Mar 2015 Location: Baltimore, MD iTrader: (0)	High-flow primary cat I just had my secondary cats replaced with straight pipe and am entertaining the idea of getting a high flow cat for the primary. Has anyone done this yet and noticed any gains? Can anyone help me out with which Magnaflow cat part number is a direct or universal fit? I feel in way over my head when browsing their selection.
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06-28-2015, 11:59 AM	#2
Eagle1oh7 Lieutenant Colonel 291 Rep 1,710 Posts Drives: '11 328i Sedan Join Date: Oct 2012 Location: Chula Vista CA iTrader: (0)	There are quite a few threads on this already. __________________ DONE: Seibon CF Hood, M3 Rep, MSport rear w/DD CF Diffuser, M3 Rep Skirts, Seibon CSL trunklid, Forgestar F14 18s w/Michelin PSS, Eisenmann catback, AA Headers, BPC Stage 2, Charcoal Delete+revMotor+AFE Drop In filter FUTURE MODS: LED headlights, CF rooftop, M3 Suspension Conversion, Dinan CAI Mod
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06-28-2015, 12:39 PM	#3
Intotheblue Private First Class 19 Rep 149 Posts Drives: 2014 650i Coupe Join Date: Mar 2015 Location: Baltimore, MD iTrader: (0)	I'm sure, but I didn't have much luck with a search, every thread seems to wander towards header talk. Last edited by Intotheblue; 06-28-2015 at 12:48 PM..
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06-28-2015, 01:54 PM	#4
Eagle1oh7 Lieutenant Colonel 291 Rep 1,710 Posts Drives: '11 328i Sedan Join Date: Oct 2012 Location: Chula Vista CA iTrader: (0)	The headers are catted if you're talking about primaries. __________________ DONE: Seibon CF Hood, M3 Rep, MSport rear w/DD CF Diffuser, M3 Rep Skirts, Seibon CSL trunklid, Forgestar F14 18s w/Michelin PSS, Eisenmann catback, AA Headers, BPC Stage 2, Charcoal Delete+revMotor+AFE Drop In filter FUTURE MODS: LED headlights, CF rooftop, M3 Suspension Conversion, Dinan CAI Mod
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06-28-2015, 02:29 PM	#5
Ali-E90 Colonel 386 Rep 2,375 Posts Drives: 2007 E90 323i (Cdn) Join Date: May 2013 Location: Toronto, Canada iTrader: (3) Garage List 2008 BMW M3 [8.00] 2007 BMW 323i [8.50]	I think OP is looking for high flow cat options that don't require changing the headers. Is this possible, or are aftermarket headers the only way to change the primary cats?
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06-28-2015, 02:52 PM	#6
Intotheblue Private First Class 19 Rep 149 Posts Drives: 2014 650i Coupe Join Date: Mar 2015 Location: Baltimore, MD iTrader: (0)	Yes exactly, headers are out of my budget. I didn't think to look how the primary cat was mounted when the car was on the lift at the exhaust shop, or if there are 1 or 2 primary cats. I'm thinking its not worth the trouble but curious anyways.
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06-29-2015, 09:07 AM	#8
TheSt\|G Resident Tamed Racing Driver 303 Rep 4,697 Posts Drives: 911, 130is, E39 M5, E36 M3 Join Date: Mar 2008 Location: Outside Philly iTrader: (2)	The primary cat is part of the header setup coming off the engine. Magnaflow cats are discount garbage for cheap cars, avoid them. __________________ 2005 E46 M3 Interlagos/Cinnamon with Sunroof Delete
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06-29-2015, 03:28 PM	#9
mike-y just another bmw douche bag 195 Rep 3,640 Posts Drives: 1.9L of fury Join Date: Nov 2008 Location: Los Angeles, CA iTrader: (4)	To do what the OP is asking, you'd have to remove your factory headers, cut out the factory cats, and weld in some sort of aftermarket cat. it's quite a bit more work than just swapping the headers.
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06-30-2015, 10:51 AM	#12
Intotheblue Private First Class 19 Rep 149 Posts Drives: 2014 650i Coupe Join Date: Mar 2015 Location: Baltimore, MD iTrader: (0)	Well count me out, definitely doesn't seem cheap enough to even consider. Thanks for the info.
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07-01-2015, 11:07 AM	#13
Rival Captain 67 Rep 790 Posts Drives: 95 z28 Join Date: Jul 2012 Location: shytown iTrader: (0)	hi flow cats have never done too well in my exp. when i was still with american V8's and now bmw's, avoid hi flow aftermarket cats. __________________ 2010 335i M sport 2008 328i 2006 325i 1995 Z28 6spd - 377rwhp rip
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07-01-2015, 11:14 AM	#14
Rival Captain 67 Rep 790 Posts Drives: 95 z28 Join Date: Jul 2012 Location: shytown iTrader: (0)	hi flow cats have never done too well in my exp. when i was still with american V8's and now bmw's, avoid hi flow aftermarket cats. __________________ 2010 335i M sport 2008 328i 2006 325i 1995 Z28 6spd - 377rwhp rip
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07-02-2015, 09:54 AM	#17
mmmnot Custom User Title 411 Rep 1,337 Posts Drives: E92 328i Join Date: Mar 2015 Location: Hotlanta iTrader: (2)	Is there a point of even calling that a 'cat' anymore? Just looks like a bloated pipe with a hole in the middle? __________________ My "build" thread
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07-02-2015, 11:30 AM	#19
hassmaschine Major General 3987 Rep 7,212 Posts Drives: "NBO" 330i Join Date: Jun 2014 Location: earth iTrader: (0)	gutting a cat isn't a good idea either. the exhaust will lose all its velocity due to the huge expansion in volume. I'd wager a gutted cat actually loses performance vs just leaving it alone, especially with them placed so close to the primaries on the stock manifolds. IMO - either do headers or don't bother messing with it at all.
	Appreciate 0 Quote

07-02-2015, 12:06 PM	#21
mmmnot Custom User Title 411 Rep 1,337 Posts Drives: E92 328i Join Date: Mar 2015 Location: Hotlanta iTrader: (2)	I just noticed the lift in a residential garage. Peanut butter and jelly. __________________ My "build" thread
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