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Thread: M3 S54 exhaust manifolds for ZHP M54

  1. #111
    Quote Originally Posted by ZHPizza View Post
    Well I am trying to move forward on this project and ran into an issue. Just posted on e46f so copying it here in case anyone is considering this...

    So I thought I would be able to pull this off without modifying the OE midsection, but it turns out I can't shorten the rear M3 header enough to fit the OE connection. I'll have to modify the midsection too to move the flanges downstream a bit.

    S54 manifolds:


    M54 manifolds:


    Front comparison - for this one, the S54 pipe COULD be shortened enough to make the M54 flange location work:


    Rear comparison - but you can't do the same with the rear:


    The S54 cat extends into where the M54 flange is, hence the need to move the flanges downstream a bit on the misdsection:


    The guy on e46f saw this and moved the midsection flanges down and shared these pics of the finished product:


    I just sent these to my buddy that's doing the fab work and I guess I'm taking him the whole damn exhaust on Monday
    If you manage to make this work then I might do the same...


    Sent from my iPhone using Tapatalk


    2006 Coupe | Black Sapphire Metallic | Natural Brown | Gruppe M Intake | Corsa TSE3 | Michelin PSS on Apex ARC-8 | Koni Yellows |

  2. #112
    Bump, any updates on this? I'm looking into doing the same on my touring for when I do the M54B30 swap.

  3. #113
    Join Date
    Nov 2016
    Location
    Charlotte, NC
    Posts
    2,578
    I abandoned the project for a few reasons:

    1. The primaries on the S54 headers are so small that they did not mate up to the stainless M54 flanges that I had bought on ebay. Smaller primaries are a good thing as you don't want the collector to be a smaller cross section than the 3 primaries, but it meant I had to do what others had done and cut the mild steel flanges off of the OE exhaust manifolds and use those.

    2. Getting the angles right was harder than I anticipated. I mocked them up on the car and then took the parts to work and barely tack welded the headers onto the flanges, thinking that I could bend the tack welds a bit to massage them into place on the car, then bring them back for finish welding.The fitment was too far off for that strategy. They'll need to be re-tacked in place while on the car. I don't have a welder at home and my car was stuck on the lift with no exhaust manifolds so I needed to get something on it that worked and had already chopped up my OE manifolds.

    3. The transition to the rest of the exhaust was going to be a bear with changing the flange placements, and I would have to neck down from the M3 2.25" exhaust diameter to mate with our 2.0" piping. That would probably be fine for this situation, especially since you're coming straight off the cats, but you really never want to neck down in an exhaust system as it will create backpressure.

    So with all that in mind and the fact that I had butchered my OE manifolds and couldn't just throw them back on, I ordered a set of 'ebay headers' on Amazon with next day shipping and got those on the car.

    The results were...ok. There was a noticeable bump in power, but the ECU seemed to be chasing the fuel trims and of course my car was now catless and just cranking out poisonous gases and honda rasp. I was already this far and liked the extra torque, so I picked up some Magnaflow high flow cats and had them welded in just behind the flanges for the headers (I'll try to grab a pic the next time I'm under the car). The cats knocked down 90% of the rasp, but the cat bodies are 4" diameter, which would be great for a forced induction car, but with NA there is a big loss of exhaust gas velocity there and it sapped away most of the power that I had picked up with the headers.

    So current state of my car:
    Ebay headers wrapped in fiberglass shit
    Magnaflow cats welded in just after the headers, beside the transmission
    maybe a little more power than stock...maybe
    cats take longer to heat up than OE so startups and first 5 mins of driving are noxious af, after that it's fine

    I'm not thrilled with it, and would rather have stock manifolds than what is currently on the car (stock was less rasp, less emissions, same-ish power), but I'll keep working on it. I have a Borla exhaust ready to go on and may try to swap the first canister on it for a 2in-2out cat to see if it the smaller cat body keeps the velocities up.

    Lmk if you want to buy some low mileage S54 headers tacked to M54 flanges for cheap:

  4. #114
    Join Date
    Nov 2014
    Location
    Portland, OR
    Posts
    9,242
    I had no idea you had attempted this. Shame it didn't work out (yet), but savor that sweet sweet reward of educating the rest of us?

  5. #115
    Join Date
    Jan 2016
    Location
    Chicago area
    Posts
    1,753
    Hmmm... it seems like the best way to get these to work would be an S54 swap.

  6. #116
    Join Date
    Oct 2016
    Location
    Vermont
    Posts
    509
    Great idea--thanks for trying and educating the rest of us! And I think holyc0w may be right...
    2004 BMW 330i ZHP (50k miles), Jet Black with black leather, MFactory LSD (3.38) with Z4 cover, 18"x8.5" ET38 APEX Arc-8's (Anthracite) with 245/40 Michelin PSS', Koni Sports with factory springs and front and rear reinforcement plates, Shark Injector, Corsa TSE3 cat-back exhaust, TMS under-driven pulleys (water & steering), CDV delete, TMS CF strut brace, K&W CAI, GAS DISA rebuild, TMS pedals, Wheelskins steering wheel cover, roller tray center console, and WeatherTech floor and cargo mats

  7. #117
    Quote Originally Posted by ZHPizza View Post
    I abandoned the project for a few reasons:

    1. The primaries on the S54 headers are so small that they did not mate up to the stainless M54 flanges that I had bought on ebay. Smaller primaries are a good thing as you don't want the collector to be a smaller cross section than the 3 primaries, but it meant I had to do what others had done and cut the mild steel flanges off of the OE exhaust manifolds and use those.

    2. Getting the angles right was harder than I anticipated. I mocked them up on the car and then took the parts to work and barely tack welded the headers onto the flanges, thinking that I could bend the tack welds a bit to massage them into place on the car, then bring them back for finish welding.The fitment was too far off for that strategy. They'll need to be re-tacked in place while on the car. I don't have a welder at home and my car was stuck on the lift with no exhaust manifolds so I needed to get something on it that worked and had already chopped up my OE manifolds.

    3. The transition to the rest of the exhaust was going to be a bear with changing the flange placements, and I would have to neck down from the M3 2.25" exhaust diameter to mate with our 2.0" piping. That would probably be fine for this situation, especially since you're coming straight off the cats, but you really never want to neck down in an exhaust system as it will create backpressure.

    So with all that in mind and the fact that I had butchered my OE manifolds and couldn't just throw them back on, I ordered a set of 'ebay headers' on Amazon with next day shipping and got those on the car.

    The results were...ok. There was a noticeable bump in power, but the ECU seemed to be chasing the fuel trims and of course my car was now catless and just cranking out poisonous gases and honda rasp. I was already this far and liked the extra torque, so I picked up some Magnaflow high flow cats and had them welded in just behind the flanges for the headers (I'll try to grab a pic the next time I'm under the car). The cats knocked down 90% of the rasp, but the cat bodies are 4" diameter, which would be great for a forced induction car, but with NA there is a big loss of exhaust gas velocity there and it sapped away most of the power that I had picked up with the headers.

    So current state of my car:
    Ebay headers wrapped in fiberglass shit
    Magnaflow cats welded in just after the headers, beside the transmission
    maybe a little more power than stock...maybe
    cats take longer to heat up than OE so startups and first 5 mins of driving are noxious af, after that it's fine

    I'm not thrilled with it, and would rather have stock manifolds than what is currently on the car (stock was less rasp, less emissions, same-ish power), but I'll keep working on it. I have a Borla exhaust ready to go on and may try to swap the first canister on it for a 2in-2out cat to see if it the smaller cat body keeps the velocities up.
    Thanks for the follow-up! Not the news I was hoping for, but I definitely appreciate your insight and experiences.


    Do you guys have emissions testing in NC? I've been thinking about doing your same plan also, but I don't know how happy the post-cat O2s would be if I moved the cats downstream, and we have OBD2 emissions testing here. The other option is the Pypes exhaust manifold that's a slightly improvement over stock.

  8. #118
    I thought the car wouldn't care THAT much about gas velocity after the collector?

    I have my headers on and the rasp is...an acquired taste. I much prefer the smooth sound of the stock exhaust, but don't want to lose the power either.

    Sent from my Pixel 2 XL using Tapatalk
    2003 Blue ZHP Sedan @ 210k
    Dead due to damaged valve. She will be resurrected.

  9. #119
    Join Date
    Nov 2016
    Location
    Charlotte, NC
    Posts
    2,578
    Quote Originally Posted by Chaplian View Post
    Thanks for the follow-up! Not the news I was hoping for, but I definitely appreciate your insight and experiences.


    Do you guys have emissions testing in NC? I've been thinking about doing your same plan also, but I don't know how happy the post-cat O2s would be if I moved the cats downstream, and we have OBD2 emissions testing here. The other option is the Pypes exhaust manifold that's a slightly improvement over stock.
    Yep, we have the same testing in NC and my car is due now. I tried many iterations of spacers to make the post cat O2 sensors happy and couldn't, so I'm going to try to move them downstream to somewhere after my magnaflow cats...once I figure out a cat setup that I like. This has been way more of a headache than finishing the S54 headers would have been. Live and learn!


    Quote Originally Posted by DeathTrap View Post
    I thought the car wouldn't care THAT much about gas velocity after the collector?

    I have my headers on and the rasp is...an acquired taste. I much prefer the smooth sound of the stock exhaust, but don't want to lose the power either.

    Sent from my Pixel 2 XL using Tapatalk
    Gotta maintain velocity to the tip, my dude. Any place where the gasses slow down means backpressure upstream. It should be fine on the S54 cats since you're necking down from the catalyst anyway - just going down to 2.0" instead of 2.25".

    The rasp of the headers without cats on stock exhaust was embarrassing for me. The fumes were even worse - I felt so bad driving through town with kids on the sidewalk or really if anyone was behind me. We've all been stuck behind catless cars breathing that nasty shit because some inconsiderate bro wanted more power. I did not like being that bro.

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