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Discussion Starter · #1 · (Edited)
Hi guys,

As title suggests, I'm currently Supecharged and have been completely catless for 3 years now (not a daily driver). However I need to install some cats in the car to clean up the stink that it leaves on my hands, hair and clothes every time I drive the car. Now It's not just about my driving pleasure anymore; when I want my wife and son to come with me I don't want to expose them (or myself for that matter) to the harmful gases i.e. CO, NOx etc. It can't be healthy longer term.

I remember when I had my primary cats gutted, I still had my secondary cats (along with stock resonator, and E-race sec 3) - the smell/fumes even then were sickening. Now, I'm running a totally catless car and whilst I love having 680bhp on tap, the fumes dampen the excitement of driving it more often!

Current Set up:
  • Stock decat headers
  • IPE catback exhaust with X pipe and cutouts

I've got a few options and wonder if anyone can help guide me here pls (since this is my 1st decat car):

1. Buy HJS 200cel sport HFC
(SUPER PRICEY)
a. I could either have them as a V band set up where the primaries would go (total cost incl HJS HFC + labour in the region of £2,500 GBP)
b. Have them installed where my secondaries would normally go (therefore chopping up the IPE a little bit - not that it matters if that helps the cause) (total cost incl HJS HFC + labour in the region of £1,700 GBP)


2. Buy RMS decat V band headers

- We all know what these are about and I could switch between cats and test pipes, however I stand to lose 30hp with stock primary cats in place (total cost incl HJS HFC + labour in the region of £2,500 GBP)


3. Have a shop fit some unknown branded 200cel HFC

- In the hope they clean up the fumes (total cost incl HFC + labour in the region of £650 GBP)


The only reason why I've not yet done anything about this issue is that I still had the nasty fumes after primary decat but WITH secondary cats, so how likely will my problem be resolved after buying other 200cel CATS?
 

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Discussion Starter · #3 ·
Curious - I've removed the primary cats but don't have a smell issue. Are you using normal E5 fuel?
I'm using 99ron here in the UK. Shell V power 99ron

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You may have already checked on this since I replied about it in another post you made about exhaust fumes a couple years ago (Fumes and smell after primary cat decat - but it was in the E60 forum and I think you replied in a later thread that you fixed the issue) if you haven't yet check the vents under the trunk liner on either side. Mine were pretty ruined and after replacing them my catless exhaust fumes in the cabin went from about a 9.5 to a 1-2 out of 10.

I was having a similar issue after putting in catless headers and it turns out it was mostly because the vents in the trunk had fallen apart and the exhaust fumes were coming into the cabin through them. I couldn't find the part on Real OEM and though the online retailers had it listed as not fitting the E60 M5 it has the same vents as any other E60. Had them replaced and no longer have issues with exhaust fumes in the cabin despite having no cats. It was pretty easy to tell they were ruined just by pulling the trunk liner out and taking a peek but this is what they looked like after removal:

View attachment 953406
 

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Coming from the world of american muscle cars where it's common to have high-strung engines without cats, there is a very particular smell associated with uncatalyzed exhaust.

The closest thing to it is 2-stroke engines (such as weed trimmers) when someone uses them and comes inside, you can smell it on their clothing.

Based on your scenario, if it were my car I would have an exhaust shop fit a replaceable high-flow cat that mates up to your current header. I would think that you could have them do that for a reasonable price, which would allow you to swap in a test pipe to go back to catless anytime it were truly wanted.

I would be willing to bet that the 20-30hp loss at peak would be totally worth it for enjoyment with the family.

My setup is RPI Cat-back, no secondary cats/resonator and eliminated the cold-start routine - no issues with exhaust odors, that cling-to-you smell that comes in if you cruise windows down.
 

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Discussion Starter · #7 ·
You may have already checked on this since I replied about it in another post you made about exhaust fumes a couple years ago (Fumes and smell after primary cat decat - but it was in the E60 forum and I think you replied in a later thread that you fixed the issue) if you haven't yet check the vents under the trunk liner on either side. Mine were pretty ruined and after replacing them my catless exhaust fumes in the cabin went from about a 9.5 to a 1-2 out of 10.
Yes, I remember your posts there - thank you for that. I bought new vent flaps from BMW and went to replace mine, only to find mine were in perfect condition already. So I have the new ones lying on my shelf for the time being. The issue is still there but perhaps my tolerance has increased?! All I know is that my clothes and hair, hands and face etc reek of it after driving the car, irrespective of windows up or down, lol!

I am curious too- as I am hesitant to remove my primaries because of the same reason.
OP may expect to inspect headers for cracks or worn manifold seals and headers gaskets.
I've had various garages and well know indys check it out and no1 found anything untoward.

Coming from the world of american muscle cars where it's common to have high-strung engines without cats, there is a very particular smell associated with uncatalyzed exhaust.

The closest thing to it is 2-stroke engines (such as weed trimmers) when someone uses them and comes inside, you can smell it on their clothing.

Based on your scenario, if it were my car I would have an exhaust shop fit a replaceable high-flow cat that mates up to your current header. I would think that you could have them do that for a reasonable price, which would allow you to swap in a test pipe to go back to catless anytime it were truly wanted.

I would be willing to bet that the 20-30hp loss at peak would be totally worth it for enjoyment with the family.

My setup is RPI Cat-back, no secondary cats/resonator and eliminated the cold-start routine - no issues with exhaust odors, that cling-to-you smell that comes in if you cruise windows down.
That's good to hear. I have been offered some stock secondary cats I may decide to buy and have a shop fit them in, but the issue has always been why wasn't the OEM secondary cats reducing the smell when I had them on the first time round (after gutting my primary cats)!? Based on that I've not done anything about my issue as I can't seem to decide should I try secondary cats again (knowing the rest of my system is new compared to before) or should I get HFC where primaries go, in which case I'd only go HJS because of its longevity, or just do RMS V band using stock primary cats.
 

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Catalytic efficiency really depends on heat, so I would think that you will have best, balanced results from a high-flow cat placed in the primary location immediately following the header.

Obviously BMW had to make some performance sacrifices in 2004/5 when this setup was being finalized, and they had to ensure the vehicle met all the stringent local variations such as California.

That being said, I would really be surprised if a current performance cat couldn't get you where you want to be - minimal performance impact but little to no exhaust odor. I think it's also important to acknowledge that the first few minutes after startup, the catalyst process isn't efficient - as with any car, I notice the difference when I first fire up in my garage vs. when I return from a trip and park.
 

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Discussion Starter · #10 ·
Catalytic efficiency really depends on heat, so I would think that you will have best, balanced results from a high-flow cat placed in the primary location immediately following the header.

Obviously BMW had to make some performance sacrifices in 2004/5 when this setup was being finalized, and they had to ensure the vehicle met all the stringent local variations such as California.

That being said, I would really be surprised if a current performance cat couldn't get you where you want to be - minimal performance impact but little to no exhaust odor. I think it's also important to acknowledge that the first few minutes after startup, the catalyst process isn't efficient - as with any car, I notice the difference when I first fire up in my garage vs. when I return from a trip and park.
I would also imagine buying HJS HFC 200cel cats and putting them where the primaries go would be a good idea but imagine if that doesn't work. I'm just a little down about it and don't seem to have much faith, other than going back to primary cats by way or RMS headers as that allows me to switch from test pipes to cats.

I have a friend who also ran IPE exhaust like me and had his primary cats deleted. He then put secondary OE cats (200cel) back in and said the exhaust become way more quite, almost a little louder than valves closed. This is something I absolutely don't want happening on mine. I love how loud the car is with valves open and also how sedate it becomes with valves closed so i'm really stuck. I don't mind spending from pocket to get the results needed but I just can't believe everyone who is fully decat is so tolerant lol.

If anybody happens to have 2ry cats for sale...in good condition.... PM me
If I don't use the ones I just bought (stock secondary cats with 75k on them), I'll let you know!
 
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I would also imagine buying HJS HFC 200cel cats and putting them where the primaries go would be a good idea but imagine if that doesn't work. I'm just a little down about it and don't seem to have much faith, other than going back to primary cats by way or RMS headers as that allows me to switch from test pipes to cats.

I have a friend who also ran IPE exhaust like me and had his primary cats deleted. He then put secondary OE cats (200cel) back in and said the exhaust become way more quite, almost a little louder than valves closed. This is something I absolutely don't want happening on mine. I love how loud the car is with valves open and also how sedate it becomes with valves closed so i'm really stuck. I don't mind spending from pocket to get the results needed but I just can't believe everyone who is fully decat is so tolerant lol.


If I don't use the ones I just bought (stock secondary cats with 75k on them), I'll let you know!
Yeah when it comes to sound everyone's preference is so subjective. I'm totally jealous that you have the valved option - I simply couldn't justify the price difference at least at the time.

Are you dead against going with a less costly performance cat, something like a Magnaflow, and then just having a decent exhaust shop fab you up the cat and the test pipe at the same time?
 

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If you gutted your 1ry cats, you're already working uphill and overloaded. For whatever reason that has NOT been openly discussed at BMW forums, the engineers went to extremes designing the 1ry cats and headers. Who builds oem headers like that? You'll have a hard time finding free flowing metal core 2ry cats to install downstream from your headers that will have as little back pressure as the oem's. And if you do, $$$$.

Have you thought of getting a used set of oem header/cats, cutting the cats out and installing them after the header collectors, with 2ries just behind? The secret will be to have a valve just before the catted exhaust section: fully catted when closed; straight pipe when opened.

As a separate note, related the downward driver door trim on 1980's Buicks and lower door "strakes" seen on 1970's Mercs,some 1960's and 70's station wagons had a (small) rear facing 3rd seat, you could drive all day long with the rear window down and not poison the kids on the 3rd row. It depended on where the exhaust was placed, usually pointed to the sides of the car behind the rear wheels, not straight back. The aerodynamics created a low pressure area that kept the fumes close to the ground, not being sucked up. This was a trend back then to allow to drive with windows down and not get dust roll from under the car into the passenger area. These were NOT fashion statements; they were there for a purpose. And these were times where cats hadn't even been invented, and fuel had lead, etc.

Look at the pics. Our engineers weren't that far off when it came to aerodynamics back then.
 

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As title suggests, I'm currently Supecharged and have been completely catless for 3 years now (not a daily driver). However I need to install some cats in the car to clean up the stink that it leaves on my hands, hair and clothes every time I drive the car. Now It's not just about my driving pleasure anymore; when I want my wife and son to come with me I don't want to expose them (or myself for that matter) to the harmful gases i.e. CO, NOx etc. It can't be healthy longer term.
I didn't read any further than this, but what you just wrote tells me that you've got an exhaust leak. I'll bet it's at the manifold to midpipe flange and on the upper segment, blowing up to the chassis and coming in via the transmission tunnel/gearstick area.
 

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Discussion Starter · #14 ·
An update... I drove to Nurburgring and back and I had no issues at all. As long as the car is moving and recirc is on and AC at times, then I can barely smell anything in the cabin. Had no headaches or ill feelings. The only time I can smell anything is in standstill traffic when the wind blows in the wrong direction and windows are open. Happy to say I don't need to add any cats back in and lose performance/sound.
 

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Discussion Starter · #16 ·
There are many stick-on CO (carbon monoxide) detectors that you just stick in the cabin. Any change in color should warn you of a possible leak.
Celicasaur, your suggestion was right on !.
Yep, I carry 2 CO2 monitors in the car. Thanks.
 
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