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Thread: M3 S54 exhaust manifolds for ZHP M54

  1. #101
    Join Date
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    Quote Originally Posted by GeorgeH View Post
    The S54 gets away with the cats that far away, why do you think that would be a problem for the M54?
    Different DME, perhaps?
    BP
    2005 330i ZHP / 6MT
    Imolarot / Naturbraun



    It's not the car you drive, it's how you drive it.

  2. #102
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    Sep 2018
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    Quote Originally Posted by ZHPizza View Post
    You would definitely have to code out the O2 sensors with the cats being that far from the engine, but I don't see why it wouldn't work. Still have to change out the flanges of course.
    Quote Originally Posted by az3579 View Post
    Different DME, perhaps?
    Yes it is a different DME, but you said "You would definitely have to code out the O2 sensors with the cats being that far from the engine" I was just wondering if you had data for that statement? I will probably end up with some kind of header setup on my ZHP inspired HPDE wagon, but I want to retain cats so moving them downstream is likely in the cards. I don't have a problem coding them out, but would prefer not to if I don't have to.
    '09 HP2S, '12GSA, '00 332iT (S54 Swapped), '00 323iT, '03 325iT, '04 ZHP IR/6MT Sedan

  3. #103
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    Quote Originally Posted by GeorgeH View Post
    Yes it is a different DME, but you said "You would definitely have to code out the O2 sensors with the cats being that far from the engine" I was just wondering if you had data for that statement? I will probably end up with some kind of header setup on my ZHP inspired HPDE wagon, but I want to retain cats so moving them downstream is likely in the cards. I don't have a problem coding them out, but would prefer not to if I don't have to.
    Just because of the different DME, really. The primary O2 sensors that set your fuel trims will still operate just fine. The M54 stock cats are right up on the block, so the DME is looking for a signal there from the secondary O2 sensor. If you remove the cats or move them down the line, then it won't look right to the DME and throw a CEL. People that add headers or move the cats downstream have to code out the secondary O2 sensors. No big deal, really. I may even have to do it with the OE S54 manifolds.

  4. #104
    See if you can get some secondary O2 logs from M3 guys running the Euro cats. I was also interested in running a cat in that location with aftermarket headers while retaining the stock DME coding and hardware.
    Quote Originally Posted by lucifer1
    You will notice quickly it is not a Honda. Welcome to BMW, for those who like working on cars just to keep it functioning.

  5. #105
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    Sep 2018
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    I would think if anything you may not be able to get the cat hot enough. But there are plenty of S54 guys who have run Euro headers and cats with stock US tunes. I don't know how the DME would know if the cats are 10" in from the header or 40", that's why I was curious to see if that same theory would apply to the M54. Also keep in mind that aftermarket cats may not be as efficient as a BMW cat, so if they are used down stream I'm not sure that means the cat location is the issue.
    '09 HP2S, '12GSA, '00 332iT (S54 Swapped), '00 323iT, '03 325iT, '04 ZHP IR/6MT Sedan

  6. #106
    Although I havenít done this with my ZHP, I had this issue with a full custom exhaust in my 2001 Jeep XJ Cherokee. Had to move the cats further back which threw a code. Pulled the header out and double wrapped it. Problem solved. The header wrap kept enough heat moving down stream that it allowed the cats to work. Granted not a BMW, but a hot running straight 6 none the less. I was thinking about trying this when I get a header for the ZHP. Anyone tried this on their BMW?


    Sent from my iPhone using Tapatalk

  7. #107
    I don't think it matters how far down the cats are as long as the mixture reads the same as stock. Now there is response time that would probably play a sizable role in whether the DME likes the new setup.

    I'm just going to use an Innovative LC-2 when that time comes.
    Quote Originally Posted by lucifer1
    You will notice quickly it is not a Honda. Welcome to BMW, for those who like working on cars just to keep it functioning.

  8. #108
    Quote Originally Posted by DeathTrap View Post
    I don't think it matters how far down the cats are as long as the mixture reads the same as stock. Now there is response time that would probably play a sizable role in whether the DME likes the new setup.

    I'm just going to use an Innovative LC-2 when that time comes.
    Cats require heat to function properly. If they are too far down stream, the dissipation of heat can result in a fault in the post-cat O2 sensor. Not reaching their designed operating temperature results in inefficiency which results in readings that are outside parameters. Hence why they are so close to the exhaust manifolds in nearly all cars from the factory.


    Sent from my iPhone using Tapatalk

  9. #109
    Quote Originally Posted by JETSET303 View Post
    Cats require heat to function properly. If they are too far down stream, the dissipation of heat can result in a fault in the post-cat O2 sensor. Not reaching their designed operating temperature results in inefficiency which results in readings that are outside parameters. Hence why they are so close to the exhaust manifolds in nearly all cars from the factory.


    Sent from my iPhone using Tapatalk
    Agreed. That's also why manufacturers are tending toward integrated manifolds. Gotta heat the cat up as fast as possible to reduce the most severe emissions from cold start.

    Legally, I know that the position of the cat cannot be more the 3" from OEM location or the EPA will get you, but ehh.

    The S54 also uses inconel for the header material, indicating that the motor runs really hot exhaust gasses through those tubes compared to the M54.

    I think a more relevant question here is how far out of spec can we go before the DME flags the cat?
    Quote Originally Posted by lucifer1
    You will notice quickly it is not a Honda. Welcome to BMW, for those who like working on cars just to keep it functioning.

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