Featured Engineering Explained: B58 Engine

Discussion in 'B58 6-Cyl Engine, Exhaust, Drivetrain, Bolt-Ons' started by JustaCarguy., Jan 23, 2019.

  1. Guff

    Guff Moderator
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    I wonder how much boost they're running :hmm:. I'm genuinely surprised they brought the compression down that much!

    The Effective Compression for the B58 in the Z4 at 11:1 comp and roughly 12psi of boost is just about 20:1 ECR. The S58 would have to run 17psi at minimum to match that 20:1 ECR, but most likely is running something like 24psi peak to get to roughly 25:1 ECR to make its 500+ hp. I know in this day and age, manufacturers (especially the Germans) are leaning on fairly substantial boost levels to make power (look at the Merc CLA45, 26+psi!), but it seems largely unnecessary with the generally good DI systems they have. I really would really like to know the rationale behind it.

    The S58 could hit the same ECR target at 21psi with 10:1 static CR, and with 11:1, it could do it at 18psi. I have no doubt that the motor would be able to handle it because a 350bar DI system should provide plenty of atomization and control as well. Plus with the electronic wastegate, Dual Vanos, advanced ignition timing, etc, knock control is probably really robust. And a higher static CR would provide a far more responsive setup, with better off boost performance, better efficiency, and more headroom going forward. Not to mention less stress on the head and turbos, which is always a bonus for reliability.

    Idk, very odd choice in my opinion, but I'm sure they did their research and testing with a variety of static CRs.
     
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  2. PerformanceSound

    PerformanceSound Well-Known Member

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    I think manufacturers are still trying to get more out of turbocharger efficiency, especially with new turbo designs allowing turbo's to be pushed longer and harder than conventional or previous generations. Not to mention easier...it would be easier to turn up the boost and make more power than spend millions on DI research.
     
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  3. A11b0ost

    A11b0ost Active Member

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    What is the injector size (cc)?
     
  4. MA617M

    MA617M Well-Known Member

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    Probably quite low given 350bar injection pressure vs port injection pressure of 3-5bar
     
  5. kona61

    kona61 Well-Known Member

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    With these injectors, you max out the hpfp (high pressure fuel pump) before the injectors limit the flow rate (from my understanding). However, you cannot upgrade the hpfp without significant modification. That is why most direct injected motors running high boost are supplemented using port injection.
     
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  6. MA617M

    MA617M Well-Known Member

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    The other differences is that the AFR 'sweet spot' on a DI engine is different than port injection, you can control cylinder temps and control the burn a lot easier - you don't need to run 11.5:1 (on 98RON) full boost on a DI engine, so there is overall less fuel consumed.

    Tuning DI is fun and there's going to be a lot of potential in the next few years when people get more comfortable with it. Like VVTi. Everyone hated it because it was scary and new, but in reality, it's absurdly simple to tune and accomodate for.
     
  7. Illsic_Design

    Illsic_Design Well-Known Member

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    Yeah with BMW engines the HPFP runs out before the injectors run out of flow. There hasn't been any upgraded hpfp's for n54, but they have finally came out with some for S55/N55 and I believe the B58 is about to have an upgraded hpfp option soon if it's not out already. More companies are starting to look into/do research on upgrading HPFP's now.
     
  8. tisdrew

    tisdrew Well-Known Member

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    Direct Injection by BMW has some insane flow rate because the hpfp rockets rail pressure over 3000psi -- that's not a typo.

    There are dozens of n54/s55 cars over 700whp on direct injection only -- there may be some in the 8's but I haven't fully done my research on the limits as port injection is easier due to the limitation of the hpfp. For those in the know of n54s, I'm referencing people using the Vargas "Shotgun" system for the hpfp. Surprisingly, the n55 is the car with the hpfp upgrade from XDI but is north of $2k for the unit.
     
  9. kona61

    kona61 Well-Known Member

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    The HPFP can’t pump much more though. The B58 runs 350 bar of fuel pressure and that’s a single hpfp instead of dual like the S55. I am not up to date on the N54 but I recall those are piezoelectric injectors and that the fuel system is fairly robust.
     

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