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1990 325i M50/ZF turbo swap, and some help requested!

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    1990 325i M50/ZF turbo swap, and some help requested!

    Hey y'all! New to the forums here, and greatly appreciate all the info I've been combing through. I'm very grateful for the ability to read and learn through your experiences!

    Earlier in the summer, I happened upon a 1990 325i, automatic, with an m20 that crapped the bed, then sat for many years (DOT code on the tires is '08). The car has zero rust, a few dings that my PDR guy can take care of, and has never been modified in any way. (except for the cassette to headphones adapter in the tape player and some aged tint, ha!)

    My goal for the car is to boost/build it for a useable horsepower curve. I would love to hit 500hp, but it's more important that my rpm range is useful and I don't have to wind it up to 4000 to get decent pull.

    Since the car has been sitting for likely more than a decade, I've purchased a new fuel tank, and a Walbro 255. After some learning, I believe I will be upgrading to run a dual pump setup with another Walbro 255. (Any leads on the parts to set this up would be greatly appreciated.) I will be tuning this for 91+ octane.

    I picked up a trashed '95 convertible with 138k for the M50B25 single vanos. TU engine I think. Found a stripped out '97 with a ZF 5 speed.
    After I amassed nearly all the parts I needed to perform the M50 swap, I happened upon a good running M54B30 as well.
    I have a Garagistic chassis mount shifter, condor motor and trans mounts, and a bunch of other odds and ends I'll be needing for the swap. (front sump pan, chase bays brake booster delete and new brake lines, pedals, etc)

    Here's where I could use a bit of guidance. I'm pulling the m50 apart to install head studs (ARP 201-4302), and run a thicker head gasket to drop the compression.
    I'd like to boost this thing silly. Are these thicker head gaskets safe to run? Last thing I want is to get this all together, and push boost through the head gasket.

    I'm also trying to decide whether I should pull the rotating assembly out of the b30 to stroke the m50, or if I should sell it to recoup some money and put that elsewhere. The b30 doesn't have a harness or ecm, so I'd rather not start gathering parts to swap that whole engine in. I'm also not sure how much work it is to swap in the b30 assy. Like, I'll need new rings and rod bearings I assume. I'm not worried about either engine having any damage, but I'm not sure how much extra work will need to be done. I'm planning to do a valve job, and I'm willing to do more machine work, but I do not want to get into buying new pistons and all that. Should I just slap the m54 block under the m50 head?

    Would also love some input on what cams to run, and which turbo would pair well. The GT35 seemed like a good option to me. I'm seeing the GT3582 for like $109, and the GT3584R that's like $450+.....what gives?

    Again, thanks in advance for any help or guidance!

    My last build was a 2006 VROD. Big bore with nitrous. The focus was reliability first and foremost, with a useable torque curve. It was amazing and consistently outperformed more powerful bikes because it we set it up correctly. It made 165hp at the back tire, and my best time was an embarassing 10.9, and you can see that I launched very soft and wasted a lot of time hitting the rev limiter.
    Here's some videos of that, and a couple pics of the m50 in current state.
    Attached Files


      The m54 entire rotating assembly would have to go in I believe. But that would give you more displacement and theoretically lower boost to hit your 500hp.

      A thick head gasket should be reliable. As an engineer who does bolted joint design, the gasket thickness doesn't really come into it. Clamping force is what's required. The arp studs should give you that.

      Can't wait to see it come together!
      "Dolphins aren't so smart, they can't even engineer an E-diff"


        You'll probably be fine with a single in-tank walbro 255. '90 has a single pump design anyway, so the next step from a 255 is just a bigger single pump unless you add a swirl pot or something.

        Confirm that engine is an M50tu.

        IMO no gasket option that lowers CR is going to be as reliable as the stock gasket.
        MLS often weep/leak coolant or just don't last long, especially if the block and head surface finish is not exactly as the MLS wants, and the flavour-of-the-month Cutring gasket+copper spacer doesn't have a spotless track record either.
        On the other hand, you won't make 500 on stock CR unless you run race gas or a healthy ethanol mix.

        The M54 bottom end will fit in the M50 block as a unit. You can't mix and match with any of the M50tu components
        M54 bottom end isn't the most stout, but should handle 500 fine.
        Probably good to do the rod bearings in addition to the mains and rings (consider gapping them on the loose side)
        I think the rings are a different material for aluminum vs iron blocks, but I'm not sure if M54 rings differ dimensionally from M50/M52.
        M54 (or M52TU - the M52 with dual vanos) heads won't fit on the single vanos block, so you can't swap the whole head, but all the guts can be swapped over if you are interested in running dual vanos from the M54.

        Harness and ECM should be reasonably easy to find at a junkyard or ebay/craigslist for the M54 if you go that route.
        The M54's MS43 ECU is pretty tunable nowadays for boost, whereas with the M50, you're probably paying for a chip tune or going for a standalone ECU. Learning curve is probably a little steeper than a standalone.
        If you are going with a standalone, something like the Link E36X is a lot of bang for the buck,


        If you run only single vanos, the M54 intake cam can have the VANOS spline shaved and then works as an intake cam for the M50. Not as aggressive as e36 M3 cams, but better than stock.
        A similar hack for the exhaust cam is an M50 Non-VANOS intake cam, with the gear mounting face shaved down.
        Both of these can't be timed with the stock cam timing blocks, but there are some aftermarket blocks on ebay to do this.

        Next step from there is E36 M3 cams, S50US/S52 are similar and can be timed with the stock blocks.

        Aftermarket stuff - Schrick 264/256, PPF/Enem Z2, etc. Any of this is going to likely need deeper valve reliefs in pistons or VANOS shims, uprated valve springs, etc.

        I don't know how GT35 sizing works, but something similar to a borg S257 with like a .7ish A/R hotside would get boost quick.
        Last edited by Northern; 01-12-2021, 07:44 AM.
        Originally posted by priapism
        My girl don't know shit, but she bakes a mean cupcake.
        Originally posted by shameson
        Usually it's best not to know how much money you have into your e30


          Thank you guys so much for the information responses!!
          I like the idea of running the dual Vanos in the M50 head.
          The s50US/52 cams will work in that combo?
          It's definitely an m50tu


            S50us/S52 cams will only work with single vanos. The intake cam's spline isn't long enough (maybe there's a workaround because apparently this spline is a separate piece?), and the exhaust cam doesn't have one at all.

            Dual vanos requires clearancing at the front of the cylinder head casting, and your ECU options narrow a bit:
            Either use the M54 MS43 ECU (as well as harness, more or less all the M54 sensors, and some trickery to convert it to a front mounted trigger wheel.),
            or a standalone that supports dual variable vanos.

            There's considerable work involved in making the dual vanos work, but it is apparently worth a bit of spool/power. Whether the work justifies the benefit is up to you.
            ba114 is currently doing this for a replacement engine for his car. He has a build thread on here and on the romraider forums.
            Originally posted by priapism
            My girl don't know shit, but she bakes a mean cupcake.
            Originally posted by shameson
            Usually it's best not to know how much money you have into your e30


              I think that I'm starting down a slippery slope. While I'm not in a big hurry to get this engine done, I'm going to hold off on all this bottom end work. I think that what I will do is opt for the more expensive aftermarket cams, sell the m54 or part it out, and run the cut ring gasket, ARP studs, and spacer to drop the cr. I'll put the money into the top end for now, running single Vanos, and if I decide to built a different bottom end for more displacement I'll do that in the future, on a stand, while the car is running and driving with this combo in it.


                For $500 more you can get low compression, forged pistons. Skip the headgasket spacer altogether.

                You want to boost it "silly" so you will need to re-gap the rings, posibbly even get new ones. Again, just buy pistons and you'll get the rings with them.

                RHD OBD2 M50b25 turbo build thread:


                  I might be into that. Do you have a link for those? Are you suggesting running the 2.5L setup or switching over to the 3.0L crank and rods?

                  edit: I'm reading through your build thread, what amazing information! Thank you so much for taking the time to document everything with so much care!
                  Last edited by HawkHammer; 01-12-2021, 07:29 PM.