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Thread: M50B25tu 3.0 Stroker + SC14 Supercharger build questions

  1. #1
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    M50B25tu 3.0 Stroker + SC14 Supercharger build questions

    Hello everyone.

    I would like to start by apologizing for asking a question that has been answered numerous times over many threads and all over the internet as well; however, I'm yet to get myself a solid answer for my case.
    Please bare with me as I'm not -by any means- an expert in this regard, hence, posting the question for all the experienced across this forum.
    I currently am a proud owner of a nice Automatic 1994 E34 520i (originally) whose previous owner decided to install an M50B25tu without updating the engine loom, ECU, or even sensors.
    Meaning that the engine as a whole is an M50B25tu, but with M50B20tu electrical parts, such as the engine loom, DME, MAF, Crank sensor...etc are Siemens.

    The engine is running OK with no issues whatsoever although I'm well aware some HP is collecting dust on table due to his poor decision. (Not trying to blame him; as I should also be blamed for not knowing the difference from the beginning, but you live and learn)


    Anyway, bedtime stories aside.. I'm now planning on stroking the engine to 3.0 using the usual engine parts and planning on installing the Toyota SC14 roots style supercharger, but, that's where I start getting confused..

    I'm well aware that building the 3.0 will require the usage of the M54B30 rotating assembly, but in each thread I came across, some use M52 rods, others use M50NV rods (since they're beefy), and others use the M54 rods..

    I'm planning to use the M50NV rods since I'm going forced induction although I heard here and there that M54 and M52 rods can hold up-to 450 ponies with no problem (could possibly be incorrect, I don't know).

    So, I'm gonna start off by replacing the engine loom with a Bosch one, and use the correct sensors, and replace the DME with a 413 red label. And swap for a 5 speed ZF. But, I'm in desperate need for some answers to the following questions.

    What Pistons am I supposed to use in order to yield a normal compression engine that can withstand around 7-9 PSI of boost?
    Are the NV rods a good choice, or am I better with M54s?
    What about fuel injectors and fuel pump?
    What about Camshafts?
    What about Piston rings gaping (if required)?
    What supporting mods am I supposed to install to support the SC14?
    Is it possible to tune the 413, or do I need a standalone?
    Recommended clutch and flywheel for the gained HP and TQ.

    And if you have any other advice or recommendation, I would highly appreciate it!

    Note: I’m not interested in Turbo builds.
    Can’t swap an S50/S52 as they’re quite scarce and expensive (if found) where I live.
    Last edited by Madd0x; 11-13-2022 at 12:54 PM.

  2. #2
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    I would axe the thought of building an 84 bore / 89 stroke engine, that is a relic from when other parts didn't exist to make better power. The M54B30 piston is the only plug-and-play option and it sucks, the M54B30/S52B32 crank sucks, there is little value to this combination if you are going to boost the engine. Take your iron block M50TU and put the M52B28 rotating assembly in it mostly for the stroke and forged crank. Make sure the bearings are good, replace the valve springs with slightly stiffer stuff (M42 springs are the same as S52 IIRC, if you want to use S52 camshafts and cam trays) and that should all you need on the engine side to survive 400whp.

    More important is the fuel and tuning IMO. Ethanol fuel is nice in that it keeps things almost as cool as if you were not boosted, but end of the day, a safe tune is how you keep a boosted engine happy no matter how strong/weak it is mechanically.
    Last edited by circuit.heart; 11-14-2022 at 02:52 PM.

  3. #3
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    Thanks for the reply, chief!

    So, you suggest the usage of the whole rotating assembly (Crank, Rods, and Pistons) from the M52B28 and have a 2.8 instead of the 3.0?

    I still don't understand why the M54B30 Crank and Pistons sucks since this is the first time I ever hear this. I would appreciate it if you could explain why.


    I found the details below copied from another thread https://www.bimmerforums.com/forum/s...4-2-8L-Stroker, but I don't seem to see what's the advantage of one over the other. (Credit to the details go to original poster)


    3.0l Stroker
    ---------------

    M50B25:
    bore: 84 mm
    stroke: 75 mm
    compression ratio: 10 , (M50TU : 10.5)
    rod length: 135, (M50B25TU:140 mm)

    M54B30:
    bore: 84 mm
    stroke: 89.6 mm
    compression ratio: 10.2
    rod length: 135 mm

    You can build a M50 3.0l stroker motor by using:
    - crank M54B30
    - rods 135 mm
    - pistonsM54B30 .

    Maybe the crank case has to be modified to clear the higher stroke crank.


    2.8l Stroker
    ---------------
    for M50B25 engine
    - crank M52B28
    - rods M20B20/23 (130 mm)
    - pistons M50B25 (non-Vanos)

    or
    - crank, from M52B28
    - rods 135 mm
    - pistons M52B28

    or
    - crank, from M52B28
    - rods 135 mm
    -pistons M50B25TU , pistons must be modified to decrease compression


    rod lengths:
    M50B25TU: 140 mm
    M50B25: 135 mm (non VANOS engine)
    M52B25: 135 mm
    M52B28: 135 mm
    M54B30: 135 mm
    M20B20: 130 mm
    M20B23: 130 mm
    M20B25: 135 mm
    M20B27: 130 mm

  4. #4
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    The M54B30 and S52B32 cranks have harmonic issues and cause all sorts of problems at high RPM’s, due to the long stroke. That’s why the oil pump nut comes off when those engines are driven hard. The M52B28 crank can be revved high without those same issues. People boost the M52B28 to 600whp+ on the stock bottom end.
    1995 525i 5-speed - Thread

  5. #5
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    What king of high RPM's are we talking about here?

    I actually wasn't planning to rev over 6.8K.

    Additionally, I've seen people welding the oil pump nut from one side in order to secure it from loosening over time.

    Edit 1: - Note: The car won't be going to tracks, this is my daily driver that I'm trying to extract more power out of since I'm tired of getting smoked by Toyota Camrys all the time. And tried of having to struggle to make the car spin the wheels from time to time.

    Edit 2: I've just started googling B30 crank harmonics and I actually just found about these issues.. I never heard or read that before. In another forum, It was mentioned that having B28 crank will get the same HP but with lesser TQs by being spun faster ofc. The problem is that I'm hungry for low end TQ.

    I really wish that swapping an M60B40 was an option, but such build will prove itself costly and quite difficult as I numerously read over many forums.
    Last edited by Madd0x; 11-15-2022 at 10:49 AM.

  6. #6
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    Quote Originally Posted by Madd0x View Post
    What king of high RPM's are we talking about here?

    I actually wasn't planning to rev over 6.8K.

    Additionally, I've seen people welding the oil pump nut from one side in order to secure it from loosening over time.

    Edit 1: - Note: The car won't be going to tracks, this is my daily driver that I'm trying to extract more power out of since I'm tired of getting smoked by Toyota Camrys all the time. And tried of having to struggle to make the car spin the wheels from time to time.

    Edit 2: I've just started googling B30 crank harmonics and I actually just found about these issues.. I never heard or read that before. In another forum, It was mentioned that having B28 crank will get the same HP but with lesser TQs by being spun faster ofc. The problem is that I'm hungry for low end TQ.

    I really wish that swapping an M60B40 was an option, but such build will prove itself costly and quite difficult as I numerously read over many forums.
    Ok, there's a lot to unpack here.

    You don't need revs to make torque especially if you are using a roots-style supercharger. Just size the pulley for the redline you want and it will make the torque you ask for.

    Welding the oil pump nut is poor. People used to do this when they didn't know the root cause, but it's 2022. The 89.1 crank whips torsionally so hard that people find the oil pump shaft snapping after they've secured the nut. You can bandage this with a harmonic damper and a chain tensioner for the oil pump chain, but it will still never run as smoothly as the 84 crank. Many racers, drifters, and restorers all note that 89.1 cranks tend to wear out the bearings faster. So for a variety of reasons, in a boosted application (just add more boost...) the longer crank is unnecessary if not counterproductive. You're adding stress to the engine already, better to build for significantly higher longevity and use a little more boost to hit the power goals.

    The M54B30 piston in particular has some design flaws and is known for high blow-by and oil consumption. That's on a factory NA 330i/530i application. Throw boost at the piston and you're quite likely to make the situation worse.

    I don't think you're hungry for low end torque, you're hungry for not having a poorly-running 2.5L swap lol. My S52 car is not painfully slow compared to even a supercharged 540i (granted, gearing). If you just want to be "not slow", a 2.8L M52 with a couple bolt-ons is comparable to modern V6 sedans and takes way less effort. More time to actually enjoy going driving.

  7. #7
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    Well that and he's got an automatic with the poorly-running 2.5L swap, so that's gotta be a bad experience.

    2.8L M52 setup with a manual will feel like a rocket in comparison. One car I put together at my shop with an S50B30US (aka an M50B30) easily kept up with tuned E34 540i's, due to being lighter and having a better-shifting manual (ZF 310z vs the clunky Getrag 420g).
    1995 525i 5-speed - Thread

  8. #8
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    Quote Originally Posted by circuit.heart View Post
    Ok, there's a lot to unpack here.

    You don't need revs to make torque especially if you are using a roots-style supercharger. Just size the pulley for the redline you want and it will make the torque you ask for.
    I meant revs for horsepower, displacement for torque.

    Welding the oil pump nut is poor. People used to do this when they didn't know the root cause, but it's 2022. The 89.1 crank whips torsionally so hard that people find the oil pump shaft snapping after they've secured the nut. You can bandage this with a harmonic damper and a chain tensioner for the oil pump chain, but it will still never run as smoothly as the 84 crank. Many racers, drifters, and restorers all note that 89.1 cranks tend to wear out the bearings faster. So for a variety of reasons, in a boosted application (just add more boost...) the longer crank is unnecessary if not counterproductive. You're adding stress to the engine already, better to build for significantly higher longevity and use a little more boost to hit the power goals.

    The M54B30 piston in particular has some design flaws and is known for high blow-by and oil consumption. That's on a factory NA 330i/530i application. Throw boost at the piston and you're quite likely to make the situation worse.
    I’m now sold on the 2.8 stroker instead of the 3.0 since I’m taking reliability into consideration.
    Which rotating assembly combination should I possibly go with of the three ones shared above?

    What would the compression ratio be?

    I don't think you're hungry for low end torque, you're hungry for not having a poorly-running 2.5L swap lol. My S52 car is not painfully slow compared to even a supercharged 540i (granted, gearing). If you just want to be "not slow", a 2.8L M52 with a couple bolt-ons is comparable to modern V6 sedans and takes way less effort. More time to actually enjoy going driving.
    Yeah yeah, an Automatic with such poor swap is giving little to no torque under 3.5k rpm. But, in high rpms the car is alive and isn’t struggling much. I pretty much hate this swap lol

    Thanks a lot for your responses. Can’t appreciate this enough.

    - - - Updated - - -

    Quote Originally Posted by dannyzabolotny View Post
    Well that and he's got an automatic with the poorly-running 2.5L swap, so that's gotta be a bad experience.

    2.8L M52 setup with a manual will feel like a rocket in comparison. One car I put together at my shop with an S50B30US (aka an M50B30) easily kept up with tuned E34 540i's, due to being lighter and having a better-shifting manual (ZF 310z vs the clunky Getrag 420g).

    You’re just adding insult to my deep injury haha.

    Thanks for the transmission recommendation too.
    Last edited by Madd0x; 11-16-2022 at 12:06 PM.

  9. #9
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    Quote Originally Posted by Madd0x View Post
    I meant revs for horsepower, displacement for torque.
    That's just not how this calculation works.

    I’m now sold on the 2.8 stroker instead of the 3.0 since I’m taking reliability into consideration.
    Which rotating assembly combination should I possibly go with of the three ones shared above?

    What would the compression ratio be?
    Stock. M52B28. Stock.

  10. #10
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    It’s significantly cheaper to stroke the engine than to swap the whole engine for an M52 around here.

    Are there any advantages for swapping the engine rather than doing a proper stroke other than M52 being lighter due to the Aluminum block?

    And it has to be converted to OBD1 as far as I know.

    I’ll dig deeper on the details of a 2.8 stroker to get as much information as possible.

    I’m glad I took the time to post the question on the forum. Without your help I would probably have gone with the 3.0

    Edit: Thanks again, Brian.

    Also I’ve just realized that you’re a software engineer just like myself.
    Last edited by Madd0x; 11-16-2022 at 03:18 PM.

  11. #11
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    Quote Originally Posted by Madd0x View Post
    It’s significantly cheaper to stroke the engine than to swap the whole engine for an M52 around here.
    That's fine, just swap the rotating assembly. Very straightforward out-and-in, you effectively end up with an OBD1 M52 like we swap in here in the USA. Even for me (staying NA) I intend to toss my S52 when it finally dies, I have a "blueprinted" M52B28 bottom end waiting for action.

  12. #12
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    Quote Originally Posted by circuit.heart View Post
    That's fine, just swap the rotating assembly. Very straightforward out-and-in, you effectively end up with an OBD1 M52 like we swap in here in the USA. Even for me (staying NA) I intend to toss my S52 when it finally dies, I have a "blueprinted" M52B28 bottom end waiting for action.
    Alright that's cool.

    Now, I'll need to be digging for more information supercharger supporting mods and see whether the Red label 413 is reliably tunable for a supercharger setup.

  13. #13
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    Quote Originally Posted by Madd0x View Post
    Now, I'll need to be digging for more information supercharger supporting mods and see whether the Red label 413 is reliably tunable for a supercharger setup.
    I would get the car running on a 2.8L OBD1 setup first with the 413 DME and see how much more power you actually need. 413's aren't the most reliable ECU and again, it's 2022, we have some really sophisticated computers now that can make the engine run smoother than BMW ever thought could be possible in 1994.

  14. #14
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    the SC14 is pretty small for the M50 / M52. Id probably look at the eaton M90. The roots style of blower will be difficult to install an intercooler. There will be significant intake heat which will pull timing, especially in hot weather or any repeated acceleration bursts. Even though the centrifugal won't look after low RPM, it will certainly make much more top end.
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  15. #15
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    I've decided for a low mileage M54B30 swap in the E34.. Yes, it's achievable and will work fine with no problems as it has been done multiple times by the guy who's going to do the swap for me (I'm not hands-on experienced with swaps and I don't have the tools).

    I got my hands on an S50B32 Individual throttle bodies with an adapter that I also am planning to put in instead of the original M54 intake manifold... however, it's not going to be a direct fit..

    Has anyone done that before? I didn't manage to find any guides or information about such process.

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