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      06-17-2013, 07:07 PM   #1
Longwong
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Did we all get it wrong? Primary vs secondary cats

So I have an x-pipe with HFC and was thinking after I bought it that maybe test pipes would have been the better choice. I was happy though and never thought about it again. Well everyone and every company has tlaked about the "primary" cats (cats closest to headers) as the most restrictive however take a look at this official bmw m3 education manual and you will see that the "primary" cats are actually the non-obstructing more flowing metallic ones and the "secondaries" are the main cats.

Makes me wonder how much more people are getting with a true xpipe vs the test pipes as TP are essentially deleting the least restrictive cat and leaving the most restrictive.

See page 62
http://www.e90fanatics.com/pdf/BMW-M...nformation.pdf
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      06-17-2013, 07:10 PM   #2
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No. No we did not.

BTW, X pipe will provide a bit more power (maybe 5-10max), however, it is widely accepted that test pipes are the best horsepower/dollar value.
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      06-17-2013, 07:17 PM   #3
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No. No we did not.

BTW, X pipe will provide a bit more power (maybe 5-10max), however, it is widely accepted that test pipes are the best horsepower/dollar value.
Well this is not informative. Did you read the official bmw training manual I posted. It clearly states the main cats are in the secondary place. Well accepted vs. what is accurate is another thing.
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      06-17-2013, 07:23 PM   #4
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The dyno doesn't lie. Remove front cats to gain 15-20 WHP. Remove secondaries to gain maybe an additional 5WHP. Many shops, forum members, tuners, and engine builders have confirmed this multiple times.
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      06-17-2013, 07:32 PM   #5
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I'm sure all the bmw reputable tuners out there did plenty of research and testing
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      06-17-2013, 07:40 PM   #6
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Quote:
Originally Posted by Longwong View Post
Well this is not informative. Did you read the official bmw training manual I posted. It clearly states the main cats are in the secondary place. Well accepted vs. what is accurate is another thing.
What's your argument then... that we have the official designated names mixed up? Do you expect people to refer to the primary cat delete as the "Catalytic Converter-Close-to-the-Engine" delete as that is what the BMW Aftersales training manual states it's called?

All I gathered from that page is that what we refer to the "secondary" cat is called the "main" cat in the manual. It doesn't state anything about actual flow characteristics between the two.
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      06-17-2013, 07:44 PM   #7
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Well the "main" cat typically means the primary in function cat. I am simply pointing it out and found it interesting that is all.
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      06-17-2013, 09:12 PM   #8
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Primary cats are most restrictive, confirmed by reputable tuners. See below

http://www.dinancars.com/university/detail.aspx?id=15

"Dinan will be making a middle racing exhaust system for the M3 similar to the one we manufacture for the M5 and M6. This racing exhaust will remove the second stage or rear catalyst"........ "This is an Ideal system for a showroom stock race car T-1 T-2 where the car must pass a smog test at the end of a race and cannot have a check engine light on. The gain about half of the front cat or 10 hp but there is no hassle and it is a lot less money. On Dinan’s middle exhaust system we also include 3 different noise level resonators so you can get the sound you are looking for from your car."
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      06-18-2013, 03:51 PM   #9
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This is not good evidence of the relative restrictiveness of the cats.
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      06-18-2013, 03:55 PM   #10
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Quote:
Originally Posted by Dashman View Post
Dude, the cats nearest the exhaust manifold are ALWAYS going to restrict the engine's breathing the most, no matter what some marketing fluff piece tells you.
this. It's common sense really. the first ones do the most work
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      06-18-2013, 04:24 PM   #11
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All I care about is the 15-20 hp gain from the test pipes.
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      06-19-2013, 02:59 AM   #12
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this. It's common sense really. the first ones do the most work
No really true. If the first ones flow much more than there is no restriction. The first set will always have the "potential" to do more but if they are less restrictive than a second set, than less surface area in the front ones may do less.

People just blow of data rather than look at it constructively. I thought it was interesting but either way I have my stock exhaust gone and is not relevent. Just thought someone may find it interesting.
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      06-19-2013, 01:03 PM   #13
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Quote:
Originally Posted by Longwong View Post
No really true. If the first ones flow much more than there is no restriction. The first set will always have the "potential" to do more but if they are less restrictive than a second set, than less surface area in the front ones may do less.

People just blow of data rather than look at it constructively. I thought it was interesting but either way I have my stock exhaust gone and is not relevent. Just thought someone may find it interesting.

not not really it's common sense that the cars (at least in USA) that are closest to the motor, the primaries, are going to do the most "filtering" of the exhaust, hence why they are 99% of the time the more restrictive set. Some cars the primary and secondary are just as restrictive so you remove them all. These cars sound wayyyy to raspy w/ no cats or resonators at all.
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      06-19-2013, 01:51 PM   #14
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The Cat between the pre/post sensors is the "primary" from

Quote:
Originally Posted by Longwong View Post
So I have an x-pipe with HFC and was thinking after I bought it that maybe test pipes would have been the better choice. I was happy though and never thought about it again. Well everyone and every company has tlaked about the "primary" cats (cats closest to headers) as the most restrictive however take a look at this official bmw m3 education manual and you will see that the "primary" cats are actually the non-obstructing more flowing metallic ones and the "secondaries" are the main cats.

Makes me wonder how much more people are getting with a true xpipe vs the test pipes as TP are essentially deleting the least restrictive cat and leaving the most restrictive.

See page 62
http://www.e90fanatics.com/pdf/BMW-M...nformation.pdf
an emissions standpoint. They would likely be the biggest restriction since they are right up in the collector merge where the gas velocity is its fastest/hottest as well.

I don't really have an argument on which is which since it doesn't really matter from a performance standpoint. The removal of the first cats produces the bigger HP gain... this has been beaten to death already.
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      06-20-2013, 10:50 AM   #15
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I have not seen any dynos with secondary cat deletes however so really cannot compare although I know that is the accepted thought. Does anyone have a before and after secondary cat delete?
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      06-20-2013, 11:39 AM   #16
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Quote:
Originally Posted by Longwong View Post
I have not seen any dynos with secondary cat deletes however so really cannot compare although I know that is the accepted thought. Does anyone have a before and after secondary cat delete?
There is very little change, if any on NA M3s.
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      06-20-2013, 12:56 PM   #17
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The primary catalysts are the ones first in the system. They do the bulk of the work and are the most restrictive. They are 400 cell units as opposed to 200 cell for the secondary units.

I am not sure why Dinan worded their statement the way they did because it is very misleading. The secondary units are NOT the main power killers in the system and that part is not clearly laid out by Dinan. However it clearly states that the system removes the catalysts that will not throw an emissions error. Diagnostically, this would only be possible by remove the catalysts after B1S2 (Bank 1 Sensor 2) and B2S2 (Bank 2 Sensor 2) since their is no monitoring being completed on those units. From an emissions standpoint, all cars have their secondary catalysts after B1S2 and B2S2.
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      06-21-2013, 12:21 AM   #18
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Quote:
Originally Posted by Longwong
I have not seen any dynos with secondary cat deletes however so really cannot compare although I know that is the accepted thought. Does anyone have a before and after secondary cat delete?
Try searching the dyno database @ www.s65dynos.com. In the search box, type "CATDL1" for primary cat delete, or "CATDL2" for secondary cat delete. Click on "view details" of the entry you want to see. If they have a baseline dyno they will show up when you click on "view details."
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      06-21-2013, 09:30 PM   #19
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Quote:
Originally Posted by Malek@MRF View Post
The primary catalysts are the ones first in the system. They do the bulk of the work and are the most restrictive. They are 400 cell units as opposed to 200 cell for the secondary units.

I am not sure why Dinan worded their statement the way they did because it is very misleading. The secondary units are NOT the main power killers in the system and that part is not clearly laid out by Dinan. However it clearly states that the system removes the catalysts that will not throw an emissions error. Diagnostically, this would only be possible by remove the catalysts after B1S2 (Bank 1 Sensor 2) and B2S2 (Bank 2 Sensor 2) since their is no monitoring being completed on those units. From an emissions standpoint, all cars have their secondary catalysts after B1S2 and B2S2.
This was not dinan this was BMW in-house training manual on the e9x m3. So unless bmw itself got it wrong I guess everyone else knows better. Has anyone flow tested the cats?
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