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    Turbo advice required

    Hi everyone, so its time to boost my M20 from my E34 525i.

    First some info from the car:

    1) Its an euro, compression ratio is 9,7:1. I would like to keep boost low and try to work with that high CR. I will tune for 95RON gas, but fill it with 97RON whenever possible. If that doesnt work, i will drop compression with a thicker gasket.
    2) Its an automatic, and i plan on keeping it that way. 4HP22 should be able to manage about 350nm/260 lbft (BMW did put the 4HP22 behind the M88/3 in south african 745i, 340nm). Specially with some improved ATF cooling. No plans on hammering it on the drag strip, so i hope it wont die too fast. Just in case i got another 4HP22 that i will rebuild for higher torque. But not just yet.
    3) Car is bifuel, with a CNG conversion. So it runs regular gas and CNG. CNG has a higher octane rating about 130RON, but the tank only has an equivalent of 22 liters of gas. So im not planning on going crazy with power when running CNG, otherwise it wont last long.
    4) No, i wont do an engine swap, i just want to boost the M20.
    5) Car is my daily driver, i dont do much driving though since i work at home. I want to keep it reliable, yet faster. Mostly highway driving and weekend drives.
    6) Currently the engine management is done by a modded MS2, running dual ignition maps (one for gas, and one for CNG). CNG system runs on a standalone neumatic/electronic system with a closed loop adjustment.
    7) For the fuel system, i got a set of 60lbs siemens injectors, a Walbro GSS341 (250lph), an aeromotive fuel regulator. On the CNG side, the regulator was modified to work with a boosted system.


    Now, since im torque limited by the trans, id like to have the widest and flatest torque curve. So charge boost to get up to 350nm as soon as possible, and hold it there till the rev limiter.

    Given im sticking with 350nm max torque, my max hp should be at 300-320bhp. Im guessing ~8ish psi based on what i've seen from other builds. Maybe a tad higher for CNG to compensate for the lower torque on that fuel.

    Now here is the question, i got a couple turbines i can pick here, i want to go for the smallest one that will do the job.
    The options are all from Masterpower.
    On the small side, the R444.


    Not sure if this is big enough to flow, if it is it could be the best option. Specially since it has an internal wastegate, which makes exhaust routing easier.

    A tad bigger, the R474.

    This one has the internal waste gate option too, but on a slightly bigger turbine. I like this option, but the internal wastegated exhaust seems to have quite a small A/R and im a bit concerned about that.

    And finally the R4449.

    Somewhat similar dimensions to the R474, but with a different ratio on the wheel sizes. But in this case there is no internal waste gate option. Which almost doubles the cost of the setup, and increases the complexity of the exhaust manifold adapter.

    So, how small can i go before the turbine turns into a buttplug? I appreciate your input.
    Last edited by Coyote_ar; 11-09-2018, 02:56 AM.
    ---E30 320i Hennarot 1984 Sedan---

    #2
    Can they provide you with turbine flow maps? Without know the mass flow vs. expansion ratio characteristics of the turbine, it's impossible for someone without experience with that specific turbo & engine combination to make a call about the ideal turbine sizing.

    If you can get maps for both compressor and turbine, you should be able to manually match points using a tool like this: http://www.turbos.bwauto.com/aftermarket/matchbot.aspx

    Comment


      #3
      Im trying to get that from them, but so far no. I only have the compressor maps.

      Im concerned mostly due to the A/R. I looked for similarly sized engines, with similar output. And looked up for turbine size.
      The EJ257 from subaru uses a VF43, which is quite similar to R474.
      IHI VF43
      Compressor
      Inducer Dia (mm) 46.5
      Exducer Dia (mm) 60
      Blades 6
      Trim 60
      Bore (mm) 6.1
      Superback Hgt (mm) 3.6

      Turbine
      Inducer Dia (mm) 53.2
      Exducer Dia (mm) 48
      Blades 11
      Trim 81
      Bearing Shaft Dia (mm) 9.0

      My concern is with the exhaust housing size. The internally wastegated housing has 6.1cm2 ... which i cant tell if that is too small or not. Conversion to A/R is a bit sketchy, since there is no linear conversion from one to the other. Some say it should be 0,41A/R which would be crazy small.

      Ill try to get exhaust map.
      Ill keep that tool at hand, thx.
      ---E30 320i Hennarot 1984 Sedan---

      Comment


        #4
        A/R is only one factor in the flow of the turbine stage. The wheel type, volute shape, all make a huge difference in both flow and efficiency.

        Comment

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