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      05-05-2020, 01:31 AM   #1
Ashley_rj
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Does any one replace their primary cats with high flow primary cats? especially s/c'd

Hi Guys,

I have a Harrop s/c e90 M3.
I have the full stock exhaust system at the moment but would like to switch to a high flow alternative. I am also a bit of an eco warrior (hypocritical I know) so don't want to go the decat route as this is my daily driver.
I would like more power (probably unnecessary as there are 490rwbhp).
There is very little info I can find about replacing the primary cats other than test pipes.

I have found that Cobra make a high flow cat'd front exhaust/up pipe/1st section or what ever it is called. As does supersprint, but I cannot find out any information as to whether this will give me some extra hp, be worth while, terribly affect my emissions.

A further option that I don't see why couldn't be done would be to cut out the primary cats and to weld in some GreenCat's or Magniflow's. If done well I dont see why that would not be a viable option???

Harrop does have a tune for a decatted exhaust, unfortunately the current staff there don't seem to be very clued up, so I have lost a bit of faith in their advice.

I would consider doing the rest of my exhaust also and will probably go for M3 world's x pipe and valved rear section.

Any info or opinions would be appreciated.
Cheers, Ash
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      05-05-2020, 05:46 AM   #2
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https://afepower.com/afe-power-49-36...ith-resonators

that is what i have and it features a 300 cel primary catalyst. oem is 400 cel. it does not have secondary cats. the two sets of catalysts work together, so if you're environmentally conscious, i'm not sure just the 300 cel cats are going to ease your guilt.
my car stinks a little bit, but i don't get a check engine light.
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      05-08-2020, 10:36 PM   #3
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Thanks roastbeef, will have a think 🤔
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      05-08-2020, 11:28 PM   #4
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Quote:
Originally Posted by roastbeef View Post
https://afepower.com/afe-power-49-36...ith-resonators

that is what i have and it features a 300 cel primary catalyst. oem is 400 cel. it does not have secondary cats. the two sets of catalysts work together, so if you're environmentally conscious, i'm not sure just the 300 cel cats are going to ease your guilt.
my car stinks a little bit, but i don't get a check engine light.
Would you pass smog with this Beef?
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      05-08-2020, 11:56 PM   #5
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Quote:
Originally Posted by Scrippy View Post
Quote:
Originally Posted by roastbeef View Post
https://afepower.com/afe-power-49-36...ith-resonators

that is what i have and it features a 300 cel primary catalyst. oem is 400 cel. it does not have secondary cats. the two sets of catalysts work together, so if you're environmentally conscious, i'm not sure just the 300 cel cats are going to ease your guilt.
my car stinks a little bit, but i don't get a check engine light.
Would you pass smog with this Beef?
Technically no, but it depends on if the dude looks under the car or not. lol
He was old and didn't bend down last year. I might try it with just switching intakes back to oem and see if I can pull one over on him.
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      05-08-2020, 11:58 PM   #6
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Any idea of your EGT's? How hard do you drive it? Why not move them down steam, Why do you want them in the primary position?
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      05-09-2020, 01:20 AM   #7
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Quote:
Originally Posted by roastbeef View Post
Quote:
Originally Posted by Scrippy View Post
Quote:
Originally Posted by roastbeef View Post
https://afepower.com/afe-power-49-36...ith-resonators

that is what i have and it features a 300 cel primary catalyst. oem is 400 cel. it does not have secondary cats. the two sets of catalysts work together, so if you're environmentally conscious, i'm not sure just the 300 cel cats are going to ease your guilt.
my car stinks a little bit, but i don't get a check engine light.
Would you pass smog with this Beef?
Technically no, but it depends on if the dude looks under the car or not. lol
He was old and didn't bend down last year. I might try it with just switching intakes back to oem and see if I can pull one over on him.
So if visually nothing was picked up would it pass? Because the last smog I had to do was nothing more than and ODB plug and 15 minutes of idling. I was used to ODB plug, a tail pipe sensor and a dyno. The guy said this is how it's done under current compliance. Granted I don't have hood louvers and a wing to prompt a look through but I wonder. If readiness is good do those cats cut it? I would like some better flow but I'd like to stay compliant, that's why I ask.
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      05-09-2020, 09:28 AM   #8
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Quote:
Originally Posted by Scrippy View Post
Quote:
Originally Posted by roastbeef View Post
Quote:
Originally Posted by Scrippy View Post
Quote:
Originally Posted by roastbeef View Post
https://afepower.com/afe-power-49-36...ith-resonators

that is what i have and it features a 300 cel primary catalyst. oem is 400 cel. it does not have secondary cats. the two sets of catalysts work together, so if you're environmentally conscious, i'm not sure just the 300 cel cats are going to ease your guilt.
my car stinks a little bit, but i don't get a check engine light.
Would you pass smog with this Beef?
Technically no, but it depends on if the dude looks under the car or not. lol
He was old and didn't bend down last year. I might try it with just switching intakes back to oem and see if I can pull one over on him.
So if visually nothing was picked up would it pass? Because the last smog I had to do was nothing more than and ODB plug and 15 minutes of idling. I was used to ODB plug, a tail pipe sensor and a dyno. The guy said this is how it's done under current compliance. Granted I don't have hood louvers and a wing to prompt a look through but I wonder. If readiness is good do those cats cut it? I would like some better flow but I'd like to stay compliant, that's why I ask.
When I first got this 300 cel xpipe, I was hoping to fly under the radar and not have to monkey with two vehicles (desert truck) for biannual smog.
I coincidentally got a check engine light about 400 miles after I put this xpipe on. However, I think it was a coincidence. I didn't address it until I had to smog about a year later and the check engine light turned out to be an o2 sensor and a cold start component. One MAY have been related to the other. I've put over 500 miles on the car since I swapped back to this xpipe and Karbonius plenum (no tune) and no check engine light.

I have to take my truck to a "star" station. I'm not sure if it is a more strict inspection, or a higher rated smog shop, but this f'n guy was crawling under my truck and pulling on hoses pretty hard. So I've seen it go both ways. The truck looks like shit and is not supposed to pass. I have to drive it 40 miles then I have a 20 mile window to get it smoged while the sensors show ready, but haven't tripped yet. Everything is there, it's just bad sensors or something.
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      05-09-2020, 10:47 PM   #9
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Quote:
Originally Posted by roastbeef View Post
When I first got this 300 cel xpipe, I was hoping to fly under the radar and not have to monkey with two vehicles (desert truck) for biannual smog.
I coincidentally got a check engine light about 400 miles after I put this xpipe on. However, I think it was a coincidence. I didn't address it until I had to smog about a year later and the check engine light turned out to be an o2 sensor and a cold start component. One MAY have been related to the other. I've put over 500 miles on the car since I swapped back to this xpipe and Karbonius plenum (no tune) and no check engine light.

I have to take my truck to a "star" station. I'm not sure if it is a more strict inspection, or a higher rated smog shop, but this f'n guy was crawling under my truck and pulling on hoses pretty hard. So I've seen it go both ways. The truck looks like shit and is not supposed to pass. I have to drive it 40 miles then I have a 20 mile window to get it smoged while the sensors show ready, but haven't tripped yet. Everything is there, it's just bad sensors or something.
Not to thread jack, but do you have any videos of this on your car? I've been trying to find how it sounds, especially with an oe muffler, but it doesn't seem many people run this one.
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      05-09-2020, 11:23 PM   #10
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Quote:
Originally Posted by Fizik View Post
Quote:
Originally Posted by roastbeef View Post
When I first got this 300 cel xpipe, I was hoping to fly under the radar and not have to monkey with two vehicles (desert truck) for biannual smog.
I coincidentally got a check engine light about 400 miles after I put this xpipe on. However, I think it was a coincidence. I didn't address it until I had to smog about a year later and the check engine light turned out to be an o2 sensor and a cold start component. One MAY have been related to the other. I've put over 500 miles on the car since I swapped back to this xpipe and Karbonius plenum (no tune) and no check engine light.

I have to take my truck to a "star" station. I'm not sure if it is a more strict inspection, or a higher rated smog shop, but this f'n guy was crawling under my truck and pulling on hoses pretty hard. So I've seen it go both ways. The truck looks like shit and is not supposed to pass. I have to drive it 40 miles then I have a 20 mile window to get it smoged while the sensors show ready, but haven't tripped yet. Everything is there, it's just bad sensors or something.
Not to thread jack, but do you have any videos of this on your car? I've been trying to find how it sounds, especially with an oe muffler, but it doesn't seem many people run this one.
My GoPro was stuck on mono sound or something, so it's not great, but you get the idea. It's paired with a vorsteiner titanium rear.
I don't think I have any clips with the oem rear. Sounds fantastic with the vorsteiner. Just ok with the oem rear exhaust. Minimal rasp.

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      05-10-2020, 12:49 AM   #11
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Do the AFE cats scrape? Most aftermarket cats in the primary location scrape since they are round and not pancake like OEM.
How much volume does the 300 cell + resonated midpipe add over stock? Iíd love to squeeze any amount of power out of the midpipes but I havenít yet since I have a super low tolerance for smell and noise.
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      05-10-2020, 12:51 AM   #12
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Quote:
Originally Posted by roastbeef View Post
Quote:
Originally Posted by Scrippy View Post
Quote:
Originally Posted by roastbeef View Post
Quote:
Originally Posted by Scrippy View Post
Quote:
Originally Posted by roastbeef View Post
https://afepower.com/afe-power-49-36...ith-resonators

that is what i have and it features a 300 cel primary catalyst. oem is 400 cel. it does not have secondary cats. the two sets of catalysts work together, so if you're environmentally conscious, i'm not sure just the 300 cel cats are going to ease your guilt.
my car stinks a little bit, but i don't get a check engine light.
Would you pass smog with this Beef?
Technically no, but it depends on if the dude looks under the car or not. lol
He was old and didn't bend down last year. I might try it with just switching intakes back to oem and see if I can pull one over on him.
So if visually nothing was picked up would it pass? Because the last smog I had to do was nothing more than and ODB plug and 15 minutes of idling. I was used to ODB plug, a tail pipe sensor and a dyno. The guy said this is how it's done under current compliance. Granted I don't have hood louvers and a wing to prompt a look through but I wonder. If readiness is good do those cats cut it? I would like some better flow but I'd like to stay compliant, that's why I ask.
When I first got this 300 cel xpipe, I was hoping to fly under the radar and not have to monkey with two vehicles (desert truck) for biannual smog.
I coincidentally got a check engine light about 400 miles after I put this xpipe on. However, I think it was a coincidence. I didn't address it until I had to smog about a year later and the check engine light turned out to be an o2 sensor and a cold start component. One MAY have been related to the other. I've put over 500 miles on the car since I swapped back to this xpipe and Karbonius plenum (no tune) and no check engine light.

I have to take my truck to a "star" station. I'm not sure if it is a more strict inspection, or a higher rated smog shop, but this f'n guy was crawling under my truck and pulling on hoses pretty hard. So I've seen it go both ways. The truck looks like shit and is not supposed to pass. I have to drive it 40 miles then I have a 20 mile window to get it smoged while the sensors show ready, but haven't tripped yet. Everything is there, it's just bad sensors or something.
I think I'll just get an axle back for now. I'm trying to locate an upgraded set of cats for better flow & noise that still keeps me compliant with CA. I'm hoping the market recognizes this and offers us something. I'm assuming the cats will be pricey but I'd rather go this type of route. Thanx for the reply!
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      05-10-2020, 03:47 AM   #13
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Scrippy- you said exactly what I was thinking. I am wondering about cutting the 400cell cats out and putting in some high flow green cats? If they fit? I am wondering if they will after some of the above comments.
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      05-10-2020, 04:05 AM   #14
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can someone post a link to these "green cats?"

also scrip, if you're ever in orange county and want to take a quick ride, let me know.
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      05-10-2020, 04:13 AM   #15
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Maybe good or not. Doesnít sound unreasonable in their description.
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      05-10-2020, 11:30 AM   #16
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Quote:
Originally Posted by Scrippy View Post
Quote:
Originally Posted by roastbeef View Post
Quote:
Originally Posted by Scrippy View Post
Quote:
Originally Posted by roastbeef View Post
https://afepower.com/afe-power-49-36...ith-resonators

that is what i have and it features a 300 cel primary catalyst. oem is 400 cel. it does not have secondary cats. the two sets of catalysts work together, so if you're environmentally conscious, i'm not sure just the 300 cel cats are going to ease your guilt.
my car stinks a little bit, but i don't get a check engine light.
Would you pass smog with this Beef?
Technically no, but it depends on if the dude looks under the car or not. lol
He was old and didn't bend down last year. I might try it with just switching intakes back to oem and see if I can pull one over on him.
So if visually nothing was picked up would it pass? Because the last smog I had to do was nothing more than and ODB plug and 15 minutes of idling. I was used to ODB plug, a tail pipe sensor and a dyno. The guy said this is how it's done under current compliance. Granted I don't have hood louvers and a wing to prompt a look through but I wonder. If readiness is good do those cats cut it? I would like some better flow but I'd like to stay compliant, that's why I ask.
Your problem is going to be visual inspection. I'm trying to figure out if I can pass with Eventuri plenum. It's OEM spec besides being carbon. I think the Eventuri badge is going to sink me.
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      05-10-2020, 07:48 PM   #17
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the problem with the kooks greencats is their lack of information. does the width and length equate to in an oem car? zero information on their website.
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      05-10-2020, 09:54 PM   #18
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Quote:
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the problem with the kooks greencats is their lack of information. does the width and length equate to in an oem car? zero information on their website.
https://gsportbygesi.com/high-perfor...tems-products/

I wonder if these are the same (and cheaper). I am just buying some second hand AP racing breaks so I will have a look at how much space there is down there for a primary cat replacement. sounds like the external dimensions are 4"...
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      05-10-2020, 10:15 PM   #19
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Quote:
Originally Posted by Ashley_rj View Post
https://gsportbygesi.com/high-perfor...tems-products/

I wonder if these are the same (and cheaper). I am just buying some second hand AP racing breaks so I will have a look at how much space there is down there for a primary cat replacement. sounds like the external dimensions are 4"...
brakes are nowhere near the catalysts sir, you can run what you want. the catalysts do get close to the transmission. the transmission has its own heat pan, and if it is really close clearance, you could easily put additional heat insulation.
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      05-10-2020, 10:17 PM   #20
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brakes are nowhere near the catalysts sir, you can run what you want. the catalysts do get close to the transmission. the transmission has its own heat pan, and if it is really close clearance, you could easily put additional heat insulation.
Haha, I know that. I was meaning while the car is in the air i can look at the exhaust
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      05-10-2020, 10:19 PM   #21
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oh i see. lol
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      05-14-2020, 02:19 AM   #22
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